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Publisher: Elsevier   (Total: 3177 journals)

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Showing 1 - 200 of 3177 Journals sorted alphabetically
Academic Pediatrics     Hybrid Journal   (Followers: 39, SJR: 1.655, CiteScore: 2)
Academic Radiology     Hybrid Journal   (Followers: 26, SJR: 1.015, CiteScore: 2)
Accident Analysis & Prevention     Partially Free   (Followers: 105, SJR: 1.462, CiteScore: 3)
Accounting Forum     Hybrid Journal   (Followers: 28, SJR: 0.932, CiteScore: 2)
Accounting, Organizations and Society     Hybrid Journal   (Followers: 42, SJR: 1.771, CiteScore: 3)
Achievements in the Life Sciences     Open Access   (Followers: 7)
Acta Anaesthesiologica Taiwanica     Open Access   (Followers: 6)
Acta Astronautica     Hybrid Journal   (Followers: 448, SJR: 0.758, CiteScore: 2)
Acta Automatica Sinica     Full-text available via subscription   (Followers: 2)
Acta Biomaterialia     Hybrid Journal   (Followers: 30, SJR: 1.967, CiteScore: 7)
Acta Colombiana de Cuidado Intensivo     Full-text available via subscription   (Followers: 3)
Acta de Investigación Psicológica     Open Access   (Followers: 2)
Acta Ecologica Sinica     Open Access   (Followers: 11, SJR: 0.18, CiteScore: 1)
Acta Histochemica     Hybrid Journal   (Followers: 5, SJR: 0.661, CiteScore: 2)
Acta Materialia     Hybrid Journal   (Followers: 326, SJR: 3.263, CiteScore: 6)
Acta Mathematica Scientia     Full-text available via subscription   (Followers: 5, SJR: 0.504, CiteScore: 1)
Acta Mechanica Solida Sinica     Full-text available via subscription   (Followers: 9, SJR: 0.542, CiteScore: 1)
Acta Oecologica     Hybrid Journal   (Followers: 12, SJR: 0.834, CiteScore: 2)
Acta Otorrinolaringologica (English Edition)     Full-text available via subscription  
Acta Otorrinolaringológica Española     Full-text available via subscription   (Followers: 2, SJR: 0.307, CiteScore: 0)
Acta Pharmaceutica Sinica B     Open Access   (Followers: 2, SJR: 1.793, CiteScore: 6)
Acta Poética     Open Access   (Followers: 4, SJR: 0.101, CiteScore: 0)
Acta Psychologica     Hybrid Journal   (Followers: 26, SJR: 1.331, CiteScore: 2)
Acta Sociológica     Open Access   (Followers: 1)
Acta Tropica     Hybrid Journal   (Followers: 7, SJR: 1.052, CiteScore: 2)
Acta Urológica Portuguesa     Open Access  
Actas Dermo-Sifiliograficas     Full-text available via subscription   (Followers: 3, SJR: 0.374, CiteScore: 1)
Actas Dermo-Sifiliográficas (English Edition)     Full-text available via subscription   (Followers: 2)
Actas Urológicas Españolas     Full-text available via subscription   (Followers: 3, SJR: 0.344, CiteScore: 1)
Actas Urológicas Españolas (English Edition)     Full-text available via subscription   (Followers: 1)
Actualites Pharmaceutiques     Full-text available via subscription   (Followers: 7, SJR: 0.19, CiteScore: 0)
Actualites Pharmaceutiques Hospitalieres     Full-text available via subscription   (Followers: 3)
Acupuncture and Related Therapies     Hybrid Journal   (Followers: 8)
Acute Pain     Full-text available via subscription   (Followers: 15, SJR: 2.671, CiteScore: 5)
Ad Hoc Networks     Hybrid Journal   (Followers: 11, SJR: 0.53, CiteScore: 4)
Addictive Behaviors     Hybrid Journal   (Followers: 18, SJR: 1.29, CiteScore: 3)
Addictive Behaviors Reports     Open Access   (Followers: 9, SJR: 0.755, CiteScore: 2)
Additive Manufacturing     Hybrid Journal   (Followers: 12, SJR: 2.611, CiteScore: 8)
Additives for Polymers     Full-text available via subscription   (Followers: 23)
Advanced Drug Delivery Reviews     Hybrid Journal   (Followers: 193, SJR: 4.09, CiteScore: 13)
Advanced Engineering Informatics     Hybrid Journal   (Followers: 12, SJR: 1.167, CiteScore: 4)
Advanced Powder Technology     Hybrid Journal   (Followers: 17, SJR: 0.694, CiteScore: 3)
Advances in Accounting     Hybrid Journal   (Followers: 9, SJR: 0.277, CiteScore: 1)
Advances in Agronomy     Full-text available via subscription   (Followers: 17, SJR: 2.384, CiteScore: 5)
Advances in Anesthesia     Full-text available via subscription   (Followers: 30, SJR: 0.126, CiteScore: 0)
Advances in Antiviral Drug Design     Full-text available via subscription   (Followers: 2)
Advances in Applied Mathematics     Full-text available via subscription   (Followers: 12, SJR: 0.992, CiteScore: 1)
Advances in Applied Mechanics     Full-text available via subscription   (Followers: 12, SJR: 1.551, CiteScore: 4)
Advances in Applied Microbiology     Full-text available via subscription   (Followers: 24, SJR: 2.089, CiteScore: 5)
Advances In Atomic, Molecular, and Optical Physics     Full-text available via subscription   (Followers: 15, SJR: 0.572, CiteScore: 2)
Advances in Biological Regulation     Hybrid Journal   (Followers: 4, SJR: 2.61, CiteScore: 7)
Advances in Botanical Research     Full-text available via subscription   (Followers: 1, SJR: 0.686, CiteScore: 2)
Advances in Cancer Research     Full-text available via subscription   (Followers: 35, SJR: 3.043, CiteScore: 6)
Advances in Carbohydrate Chemistry and Biochemistry     Full-text available via subscription   (Followers: 9, SJR: 1.453, CiteScore: 2)
Advances in Catalysis     Full-text available via subscription   (Followers: 5, SJR: 1.992, CiteScore: 5)
Advances in Cell Aging and Gerontology     Full-text available via subscription   (Followers: 5)
Advances in Cellular and Molecular Biology of Membranes and Organelles     Full-text available via subscription   (Followers: 14)
Advances in Chemical Engineering     Full-text available via subscription   (Followers: 29, SJR: 0.156, CiteScore: 1)
Advances in Child Development and Behavior     Full-text available via subscription   (Followers: 11, SJR: 0.713, CiteScore: 1)
Advances in Chronic Kidney Disease     Full-text available via subscription   (Followers: 11, SJR: 1.316, CiteScore: 2)
Advances in Clinical Chemistry     Full-text available via subscription   (Followers: 26, SJR: 1.562, CiteScore: 3)
Advances in Colloid and Interface Science     Full-text available via subscription   (Followers: 20, SJR: 1.977, CiteScore: 8)
Advances in Computers     Full-text available via subscription   (Followers: 14, SJR: 0.205, CiteScore: 1)
Advances in Dermatology     Full-text available via subscription   (Followers: 15)
Advances in Developmental Biology     Full-text available via subscription   (Followers: 13)
Advances in Digestive Medicine     Open Access   (Followers: 12)
Advances in DNA Sequence-Specific Agents     Full-text available via subscription   (Followers: 7)
Advances in Drug Research     Full-text available via subscription   (Followers: 26)
Advances in Ecological Research     Full-text available via subscription   (Followers: 44, SJR: 2.524, CiteScore: 4)
Advances in Engineering Software     Hybrid Journal   (Followers: 29, SJR: 1.159, CiteScore: 4)
Advances in Experimental Biology     Full-text available via subscription   (Followers: 8)
Advances in Experimental Social Psychology     Full-text available via subscription   (Followers: 52, SJR: 5.39, CiteScore: 8)
Advances in Exploration Geophysics     Full-text available via subscription   (Followers: 1)
Advances in Fluorine Science     Full-text available via subscription   (Followers: 9)
Advances in Food and Nutrition Research     Full-text available via subscription   (Followers: 67, SJR: 0.591, CiteScore: 2)
Advances in Fuel Cells     Full-text available via subscription   (Followers: 17)
Advances in Genetics     Full-text available via subscription   (Followers: 21, SJR: 1.354, CiteScore: 4)
Advances in Genome Biology     Full-text available via subscription   (Followers: 11, SJR: 12.74, CiteScore: 13)
Advances in Geophysics     Full-text available via subscription   (Followers: 7, SJR: 1.193, CiteScore: 3)
Advances in Heat Transfer     Full-text available via subscription   (Followers: 26, SJR: 0.368, CiteScore: 1)
Advances in Heterocyclic Chemistry     Full-text available via subscription   (Followers: 11, SJR: 0.749, CiteScore: 3)
Advances in Human Factors/Ergonomics     Full-text available via subscription   (Followers: 26)
Advances in Imaging and Electron Physics     Full-text available via subscription   (Followers: 3, SJR: 0.193, CiteScore: 0)
Advances in Immunology     Full-text available via subscription   (Followers: 37, SJR: 4.433, CiteScore: 6)
Advances in Inorganic Chemistry     Full-text available via subscription   (Followers: 10, SJR: 1.163, CiteScore: 2)
Advances in Insect Physiology     Full-text available via subscription   (Followers: 2, SJR: 1.938, CiteScore: 3)
Advances in Integrative Medicine     Hybrid Journal   (Followers: 6, SJR: 0.176, CiteScore: 0)
Advances in Intl. Accounting     Full-text available via subscription   (Followers: 3)
Advances in Life Course Research     Hybrid Journal   (Followers: 9, SJR: 0.682, CiteScore: 2)
Advances in Lipobiology     Full-text available via subscription   (Followers: 1)
Advances in Magnetic and Optical Resonance     Full-text available via subscription   (Followers: 8)
Advances in Marine Biology     Full-text available via subscription   (Followers: 21, SJR: 0.88, CiteScore: 2)
Advances in Mathematics     Full-text available via subscription   (Followers: 15, SJR: 3.027, CiteScore: 2)
Advances in Medical Sciences     Hybrid Journal   (Followers: 9, SJR: 0.694, CiteScore: 2)
Advances in Medicinal Chemistry     Full-text available via subscription   (Followers: 6)
Advances in Microbial Physiology     Full-text available via subscription   (Followers: 5, SJR: 1.158, CiteScore: 3)
Advances in Molecular and Cell Biology     Full-text available via subscription   (Followers: 25)
Advances in Molecular and Cellular Endocrinology     Full-text available via subscription   (Followers: 8)
Advances in Molecular Toxicology     Full-text available via subscription   (Followers: 7, SJR: 0.182, CiteScore: 0)
Advances in Nanoporous Materials     Full-text available via subscription   (Followers: 5)
Advances in Oncobiology     Full-text available via subscription   (Followers: 2)
Advances in Organ Biology     Full-text available via subscription   (Followers: 2)
Advances in Organometallic Chemistry     Full-text available via subscription   (Followers: 18, SJR: 1.875, CiteScore: 4)
Advances in Parallel Computing     Full-text available via subscription   (Followers: 7, SJR: 0.174, CiteScore: 0)
Advances in Parasitology     Full-text available via subscription   (Followers: 5, SJR: 1.579, CiteScore: 4)
Advances in Pediatrics     Full-text available via subscription   (Followers: 27, SJR: 0.461, CiteScore: 1)
Advances in Pharmaceutical Sciences     Full-text available via subscription   (Followers: 19)
Advances in Pharmacology     Full-text available via subscription   (Followers: 17, SJR: 1.536, CiteScore: 3)
Advances in Physical Organic Chemistry     Full-text available via subscription   (Followers: 9, SJR: 0.574, CiteScore: 1)
Advances in Phytomedicine     Full-text available via subscription  
Advances in Planar Lipid Bilayers and Liposomes     Full-text available via subscription   (Followers: 3, SJR: 0.109, CiteScore: 1)
Advances in Plant Biochemistry and Molecular Biology     Full-text available via subscription   (Followers: 11)
Advances in Plant Pathology     Full-text available via subscription   (Followers: 6)
Advances in Porous Media     Full-text available via subscription   (Followers: 5)
Advances in Protein Chemistry     Full-text available via subscription   (Followers: 19)
Advances in Protein Chemistry and Structural Biology     Full-text available via subscription   (Followers: 20, SJR: 0.791, CiteScore: 2)
Advances in Psychology     Full-text available via subscription   (Followers: 68)
Advances in Quantum Chemistry     Full-text available via subscription   (Followers: 6, SJR: 0.371, CiteScore: 1)
Advances in Radiation Oncology     Open Access   (Followers: 2, SJR: 0.263, CiteScore: 1)
Advances in Small Animal Medicine and Surgery     Hybrid Journal   (Followers: 3, SJR: 0.101, CiteScore: 0)
Advances in Space Biology and Medicine     Full-text available via subscription   (Followers: 6)
Advances in Space Research     Full-text available via subscription   (Followers: 433, SJR: 0.569, CiteScore: 2)
Advances in Structural Biology     Full-text available via subscription   (Followers: 5)
Advances in Surgery     Full-text available via subscription   (Followers: 13, SJR: 0.555, CiteScore: 2)
Advances in the Study of Behavior     Full-text available via subscription   (Followers: 37, SJR: 2.208, CiteScore: 4)
Advances in Veterinary Medicine     Full-text available via subscription   (Followers: 20)
Advances in Veterinary Science and Comparative Medicine     Full-text available via subscription   (Followers: 15)
Advances in Virus Research     Full-text available via subscription   (Followers: 6, SJR: 2.262, CiteScore: 5)
Advances in Water Resources     Hybrid Journal   (Followers: 54, SJR: 1.551, CiteScore: 3)
Aeolian Research     Hybrid Journal   (Followers: 6, SJR: 1.117, CiteScore: 3)
Aerospace Science and Technology     Hybrid Journal   (Followers: 388, SJR: 0.796, CiteScore: 3)
AEU - Intl. J. of Electronics and Communications     Hybrid Journal   (Followers: 8, SJR: 0.42, CiteScore: 2)
African J. of Emergency Medicine     Open Access   (Followers: 6, SJR: 0.296, CiteScore: 0)
Ageing Research Reviews     Hybrid Journal   (Followers: 12, SJR: 3.671, CiteScore: 9)
Aggression and Violent Behavior     Hybrid Journal   (Followers: 488, SJR: 1.238, CiteScore: 3)
Agri Gene     Hybrid Journal   (Followers: 1, SJR: 0.13, CiteScore: 0)
Agricultural and Forest Meteorology     Hybrid Journal   (Followers: 18, SJR: 1.818, CiteScore: 5)
Agricultural Systems     Hybrid Journal   (Followers: 32, SJR: 1.156, CiteScore: 4)
Agricultural Water Management     Hybrid Journal   (Followers: 45, SJR: 1.272, CiteScore: 3)
Agriculture and Agricultural Science Procedia     Open Access   (Followers: 4)
Agriculture and Natural Resources     Open Access   (Followers: 3)
Agriculture, Ecosystems & Environment     Hybrid Journal   (Followers: 58, SJR: 1.747, CiteScore: 4)
Ain Shams Engineering J.     Open Access   (Followers: 5, SJR: 0.589, CiteScore: 3)
Air Medical J.     Hybrid Journal   (Followers: 8, SJR: 0.26, CiteScore: 0)
AKCE Intl. J. of Graphs and Combinatorics     Open Access   (SJR: 0.19, CiteScore: 0)
Alcohol     Hybrid Journal   (Followers: 12, SJR: 1.153, CiteScore: 3)
Alcoholism and Drug Addiction     Open Access   (Followers: 12)
Alergologia Polska : Polish J. of Allergology     Full-text available via subscription   (Followers: 1)
Alexandria Engineering J.     Open Access   (Followers: 2, SJR: 0.604, CiteScore: 3)
Alexandria J. of Medicine     Open Access   (Followers: 1, SJR: 0.191, CiteScore: 1)
Algal Research     Partially Free   (Followers: 11, SJR: 1.142, CiteScore: 4)
Alkaloids: Chemical and Biological Perspectives     Full-text available via subscription   (Followers: 2)
Allergologia et Immunopathologia     Full-text available via subscription   (Followers: 1, SJR: 0.504, CiteScore: 1)
Allergology Intl.     Open Access   (Followers: 5, SJR: 1.148, CiteScore: 2)
Alpha Omegan     Full-text available via subscription   (SJR: 3.521, CiteScore: 6)
ALTER - European J. of Disability Research / Revue Européenne de Recherche sur le Handicap     Full-text available via subscription   (Followers: 11, SJR: 0.201, CiteScore: 1)
Alzheimer's & Dementia     Hybrid Journal   (Followers: 54, SJR: 4.66, CiteScore: 10)
Alzheimer's & Dementia: Diagnosis, Assessment & Disease Monitoring     Open Access   (Followers: 6, SJR: 1.796, CiteScore: 4)
Alzheimer's & Dementia: Translational Research & Clinical Interventions     Open Access   (Followers: 6, SJR: 1.108, CiteScore: 3)
Ambulatory Pediatrics     Hybrid Journal   (Followers: 5)
American Heart J.     Hybrid Journal   (Followers: 58, SJR: 3.267, CiteScore: 4)
American J. of Cardiology     Hybrid Journal   (Followers: 67, SJR: 1.93, CiteScore: 3)
American J. of Emergency Medicine     Hybrid Journal   (Followers: 47, SJR: 0.604, CiteScore: 1)
American J. of Geriatric Pharmacotherapy     Full-text available via subscription   (Followers: 13)
American J. of Geriatric Psychiatry     Hybrid Journal   (Followers: 14, SJR: 1.524, CiteScore: 3)
American J. of Human Genetics     Hybrid Journal   (Followers: 37, SJR: 7.45, CiteScore: 8)
American J. of Infection Control     Hybrid Journal   (Followers: 29, SJR: 1.062, CiteScore: 2)
American J. of Kidney Diseases     Hybrid Journal   (Followers: 37, SJR: 2.973, CiteScore: 4)
American J. of Medicine     Hybrid Journal   (Followers: 50)
American J. of Medicine Supplements     Full-text available via subscription   (Followers: 3, SJR: 1.967, CiteScore: 2)
American J. of Obstetrics and Gynecology     Hybrid Journal   (Followers: 272, SJR: 2.7, CiteScore: 4)
American J. of Ophthalmology     Hybrid Journal   (Followers: 66, SJR: 3.184, CiteScore: 4)
American J. of Ophthalmology Case Reports     Open Access   (Followers: 5, SJR: 0.265, CiteScore: 0)
American J. of Orthodontics and Dentofacial Orthopedics     Full-text available via subscription   (Followers: 6, SJR: 1.289, CiteScore: 1)
American J. of Otolaryngology     Hybrid Journal   (Followers: 25, SJR: 0.59, CiteScore: 1)
American J. of Pathology     Hybrid Journal   (Followers: 32, SJR: 2.139, CiteScore: 4)
American J. of Preventive Medicine     Hybrid Journal   (Followers: 28, SJR: 2.164, CiteScore: 4)
American J. of Surgery     Hybrid Journal   (Followers: 39, SJR: 1.141, CiteScore: 2)
American J. of the Medical Sciences     Hybrid Journal   (Followers: 12, SJR: 0.767, CiteScore: 1)
Ampersand : An Intl. J. of General and Applied Linguistics     Open Access   (Followers: 7)
Anaerobe     Hybrid Journal   (Followers: 4, SJR: 1.144, CiteScore: 3)
Anaesthesia & Intensive Care Medicine     Full-text available via subscription   (Followers: 67, SJR: 0.138, CiteScore: 0)
Anaesthesia Critical Care & Pain Medicine     Full-text available via subscription   (Followers: 25, SJR: 0.411, CiteScore: 1)
Anales de Cirugia Vascular     Full-text available via subscription   (Followers: 1)
Anales de Pediatría     Full-text available via subscription   (Followers: 3, SJR: 0.277, CiteScore: 0)
Anales de Pediatría (English Edition)     Full-text available via subscription  
Anales de Pediatría Continuada     Full-text available via subscription  
Analytic Methods in Accident Research     Hybrid Journal   (Followers: 5, SJR: 4.849, CiteScore: 10)
Analytica Chimica Acta     Hybrid Journal   (Followers: 44, SJR: 1.512, CiteScore: 5)
Analytica Chimica Acta : X     Open Access  
Analytical Biochemistry     Hybrid Journal   (Followers: 217, SJR: 0.633, CiteScore: 2)
Analytical Chemistry Research     Open Access   (Followers: 13, SJR: 0.411, CiteScore: 2)
Analytical Spectroscopy Library     Full-text available via subscription   (Followers: 14)
Anesthésie & Réanimation     Full-text available via subscription   (Followers: 2)
Anesthesiology Clinics     Full-text available via subscription   (Followers: 25, SJR: 0.683, CiteScore: 2)
Angiología     Full-text available via subscription   (SJR: 0.121, CiteScore: 0)
Angiologia e Cirurgia Vascular     Open Access   (Followers: 1, SJR: 0.111, CiteScore: 0)
Animal Behaviour     Hybrid Journal   (Followers: 230, SJR: 1.58, CiteScore: 3)
Animal Feed Science and Technology     Hybrid Journal   (Followers: 7, SJR: 0.937, CiteScore: 2)
Animal Reproduction Science     Hybrid Journal   (Followers: 7, SJR: 0.704, CiteScore: 2)

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Similar Journals
Journal Cover
Agricultural Water Management
Journal Prestige (SJR): 1.272
Citation Impact (citeScore): 3
Number of Followers: 45  
  Hybrid Journal Hybrid journal (It can contain Open Access articles)
ISSN (Print) 0378-3774
Published by Elsevier Homepage  [3177 journals]
  • Adaptation of paddy rice in China to climate change: The effects of
           shifting sowing date on yield and irrigation water requirement
    • Abstract: Publication date: 20 February 2020Source: Agricultural Water Management, Volume 228Author(s): Yimin Ding, Weiguang Wang, Qianlai Zhuang, Yufeng LuoAbstractWarming and increasing extreme climate events are expected to reduce crop yields including rice production in China, threatening the Chinese food security. Shifting sowing date has been considered as a key adaptation strategy to sustain rice production in China. However, the extent to which it can mitigate the adverse climate change impact on yield and whether more irrigation is required remains unclear. Here, by driving ORYZA v3 with four climate models (GCMs), we analyzed the impacts of climate change on China rice yield and net irrigation water requirement (NIR) at 21 sites under a wide range of sowing date. We found that without altering sowing date, weighted average rice yield for all sites will decline 5.1, 7.3 and 15.1% in periods 2011–2040, 2041–2070 and 2071–2100, respectively. Yields losses in temperate zones are linked to increased crop development rates with higher temperatures, but in subtropical regions, the reduction is more related to the damage of heat stress during rice heading or flowering periods. NIR increases notably in all regions (up to 71%) except northeastern China, where the shortened growth duration resulted in less time to consume water. When the optimized sowing date is applied, average yield losses will be effectively compensated. To achieve these, rice-sowing date will be shifted by up to 54 days and on average 17.8–23.4 % more fresh water in future periods are needed to meet the water requirement of rice growth. We also found that, due to increasing the frequency of heat events, farmers in Chinese rice production regions (e.g., Yangtze River Basin) will have narrow sowing windows at the end of this century. This study suggests that adequate irrigation and adjusting sowing dates could mitigate the negative climate impacts on rice production in China.
  • Nitrogen interception and fate in vegetated ditches using the isotope
           tracer method: A simulation study in northern China
    • Abstract: Publication date: 20 February 2020Source: Agricultural Water Management, Volume 228Author(s): Xiaona Li, Weiwei Zhang, Chunqiao Zhao, Hongjie Li, Ruishuang ShiAbstractDuring periods of heavy precipitation, farmland drainage ditches are the main routes for farmland nitrogen flowing into surface waters in northern China. Vegetated ditches can be engineered to mitigate N loss from agricultural runoff. We used a simulation study to evaluate the interception of nitrogen in a ditch without vegetation and three vegetated ditches. The 15N stable isotope tracer method was used to analyze the fate of ditch intercepting farmland runoff nitrogen. The three vegetated ditches were planted with Lolium perenne L., Bromus inermis Leyss. and Elytrigia repens (L.) Nevski. The results showed that the interception rates of nitrogen in the three vegetated ditches were higher than in the ditch without vegetation. The L. perenne ditch had the lowest interception rates of nitrogen among the three vegetated ditches. The interception of nitrogen by the three vegetated ditches was primarily achieved by the capture of nitrogen runoff in the soil ditch bed, which allowed water infiltration. Nitrogen retained in the ditch bed soil of the ditch without vegetation was enriched in the 0–10 cm soil layer from surface mainly. However, in the three vegetated ditches, it was transported to the 50 cm soil layer. All of the nitrogen retained in the vegetated ditches was absorbed by the L. Perenne and E. repens, and the interception of nitrogen was affected by plant species and growth stage in the vegetated ditch.
  • Water-saving irrigation is a ‘win-win’ management strategy in rice
           paddies – With both reduced greenhouse gas emissions and enhanced water
           use efficiency
    • Abstract: Publication date: 20 February 2020Source: Agricultural Water Management, Volume 228Author(s): Hong Wang, Yan Zhang, Yaojun Zhang, Marshall D. McDaniel, Lan Sun, Wei Su, Xiaorong Fan, Shuhua Liu, Xin XiaoAbstractDemand for rice will increase with growing global population. Globally, water management and nitrogen (N) application are two key factors influencing rice production and greenhouse gases (GHGs) emissions. In China, one of the world’s largest rice-producing countries, scarcity of water also threatens rice production. Therefore, in order to meet these challenges, it is essential to find water-use efficient irrigation management that also mitigates GHGs emissions from rice paddies. This study was conducted with three N application rates (90, 180, 270 kg N ha−1) under two irrigation regimes: 1) the conventional flooding-midseason drainage-flooding irrigation (FDF), and 2) flooding-moist by alternating wetting and drying (AWD) as the water-saving irrigation. Results showed that AWD irrigation significantly reduced CH4 emissions by 38%, but increased N2O emissions by 34%. Although N2O and CH4 emissions showed a trade-off relationship, the global warming potential (GWP) and greenhouse gas intensity (GHGI) significantly decreased by 22% and 24%, respectively, under water-saving irrigation management. N fertilization significantly enhanced rice grain yield but had no effects on water use efficiency (WUE). Although AWD had no effects on rice grain yield, it significantly enhanced WUE by 40%. Considering the interactive effects of N fertilization and irrigation management, the highest grain yield (7808.38 kg ha−1) occurred in AWD with medium N application rate. Generally, AWD irrigation regime could be used as an effective management for simultaneously saving water and enhancing rice grain yield, while mitigating GHGs emissions from rice paddies.
  • Application of fuzzy-genetic and regularization random forest (FG-RRF):
           Estimation of crop evapotranspiration (ET c ) for maize and wheat crops
    • Abstract: Publication date: Available online 30 November 2019Source: Agricultural Water ManagementAuthor(s): Mandeep Kaur Saggi, Sushma JainAbstractSmart farming has played a significant role in decision support system to maximize the yield with minimum consumption of water in the field of agriculture. The main objective of this paper is to design and develop an innovative multilevel model ensembling for accurate estimation of crop coefficient (Kc) and reference evapotranspiration (ETc) using Fuzzy-Genetic (FG) and Regularization Random Forest(RRF) models. This study present the water requirement of three crops namely (maize, wheat1 and wheat2) in which ETc is a function of the product of the crop coefficient Kc and reference evapotranspiration (ETo). The proposed model is used to analyze the data collected by IMD, Pune and PAU, Ludhiana (case study) for decision making in a crop water model. The proposed FG-RRF(ETc) crop prediction model efficiently estimated Kc and ETc and make an efficient decision.
  • Changes in root hydraulic conductance in relation to the overall growth
           response of maize seedlings to partial root-zone nitrogen application
    • Abstract: Publication date: Available online 29 November 2019Source: Agricultural Water ManagementAuthor(s): Niu Xiaoli, Zhou Hanmi, Wang Xiukang, Hu Tiantian, Feng Puyu, Li Ting, Zhao Na, Yin DongxueAbstractThe influence mechanism of heterogeneous nutrient distribution on compensatory growth of maize seedlings is a key topic in the interaction between crops and soil environment. We evaluated the significance of root hydraulic conductance (Lp) and related parameter changes in water uptake and growth regulation of plants under different nitrogen (N) conditions. Maize seedlings were grown in split-root containers containing N solutions. Three N treatments were applied: (1) full-strength N (control: C), in which both sub-root systems received 4.0 mM N (each sub-root: C44); (2) partial N deficit (D), in which each sub-root system received 2.0 mM N (D42) or full-strength N (D44); and (3) partial N resupply (S), in which both sub-root systems received 2.0 mM N for six days, followed by 2.0 mM N (S22) or full-strength N (S24). The shoot dry mass in D increased gradually with early development, and was greater than that in C and S within 15–21 day, suggesting that the superiority of partial N deficit (D) in term of maize seedling growth was apparent and caused compensatory growth. Moreover, the slope and intercept in D44 and D42 between ΨL vs. Lp and shoot N content vs. Lp were obviously greater than that in C44, S24 and S22, indicating that higher plant dry mass in D might be attributable to the maintenance of a similar ΨL and improved shoot N content. In addition, the slopes and intercepts in D44 and D42 between Lp vs. root surface area and shoot N content vs. root surface area were higher than that in S24 and S22, suggesting that compared with partial N resupply, partial N deficit was more advantageous to root water uptake and N accumulation at the same level of root surface area, thus resulted in higher dry mass of maize seedlings. However, partial N resupply significantly increased root cortex thickness/diameter ratio and reduced root vessel diameter, which resulted in lower Lp, ΨL and shoot N content during 12–21 day. Unexpectedly, at 21 day, the shoot dry mass in S could recover to the level of control. The regulation mechanisms in partial N resupply will be the focus of future studies. Thus, when adopting the method of partial N application, it is necessary to consider the soil N condition before partial application.
  • Field trials to detect drainage pipe networks using thermal and RGB data
           from unmanned aircraft
    • Abstract: Publication date: Available online 27 November 2019Source: Agricultural Water ManagementAuthor(s): C.B. Kratt, D.K. Woo, K.N. Johnson, M. Haagsma, P. Kumar, J. Selker, S. TylerAbstractThe use of drainage pipe is documented as far back as 200 B. C. and continues to be used in poorly drained agricultural regions throughout the world. While good for crop production, the eco-hydrologic impacts of this modification have been shown to adversely affect natural drainage networks. Identifying the exact location of drainage pipe networks is essential to developing groundwater and surface water models. The geometry of drainage pipe networks installed decades ago has often been lost with time or was never well documented in the first place. Previous work has recognized that drainage pipes can be observed for certain soil types in visible spectrum (RGB) remote sensing data due to changes in soil albedo. In this work, small Unmanned Aerial Systems (sUAS) were used to collect high resolution RGB and thermal data to map subsurface drainage pipe. Within less than 96 h of a small (< 1.3 cm) rain event, a total of approximately 60 ha of sUAS thermal and RGB data were acquired at two different locations in the IML-CZO in Illinois. The thermal imagery showed limited evidence of thermal contrast related to the drainage pipe. If the data were acquired immediately after a rain event it is more likely a temperature contrast would have been detected due to lower soil moisture proximal to the drainage pipe network. The RGB data, however, elucidated the drainage pipe entirely at one site and elucidated traces of the drainage pipe at the other site. These results illustrate the importance of the timing of sUAS data collection with respect to the precipitation event. Ongoing related work focusing on laboratory and numerical experiments to better quantify feedbacks between albedo, soil moisture, and heat transfer will help predict the optimal timing of data collection for applications such as drainage pipe mapping.
  • Divergent agricultural water governance scenarios: The case of Zayanderud
           basin, Iran
    • Abstract: Publication date: Available online 26 November 2019Source: Agricultural Water ManagementAuthor(s): Neda Nazemi, Rider W. Foley, Garrick Louis, Lauren Withycombe KeelerAbstractThere is an urgent need to consider adaptation strategies for agricultural water resources in response to the ever-growing demand for freshwater around the world. This is especially poignant in arid and semi-arid regions, like the Middle East and North Africa (MENA) where water resources have been extremely limited historically. Today, water resources are declining due to a variety of factors, including climate change, population growth and changing food preferences. Research on this topic typically seeks to assess the impact of discreet alternative interventions in isolation. However, it is necessary to analyze the broader factors affecting agricultural water management as interconnected components of a complex water governance system within a specific geographic context. This research uses an exploratory, formative scenario planning approach to a) identify important adaptation strategies, b) use those adaptation strategies to construct a small set of coherent, plausible and diverse regional agricultural water governance scenarios, and c) analyze future scenarios of the Zayandehroud watershed in Iran in the year 2040. The research shares five scenarios that exemplify divergent adaptation and mitigation approaches to agriculture water demand in Zayandehroud watershed, including adhering to the status quo. Each scenario embodies different economic and political priorities to reveal how those priorities impact the ecological, social, and economic sustainability of this watershed. These scenarios provide insights into the long-term implications of near-term decisions about water and food security, resilience of local communities and the ecological integrity of the regional watershed. This research explores the conceptual relationships between components of the water governance system and demonstrates an approach to analyzing alternative constellations of factors that will impact agricultural water management. Policy-makers can make more effective policies if they consider how to transform the broader system of regional water governance, rather than only evaluating discrete agricultural water management projects on a project-by-project basis.
  • Multi-stakeholder analysis to improve agricultural water management policy
           and practice in Malta
    • Abstract: Publication date: Available online 26 November 2019Source: Agricultural Water ManagementAuthor(s): D. D’Agostino, M. Borg, S.H. Hallett, R.S. Sakrabani, A. Thompson, L. Papadimitriou, J.W. KnoxAbstractMalta faces a raft of water challenges which are negatively impacting on the sustainability of irrigated agriculture, and creating serious tensions with other sectors competing for water, including urban development, tourism and the environment. In this paper we argue for a transparent process centred on participatory stakeholder engagement to agree on the most challenging water-related risks and to identify solutions that both support the water governance framework and improve on-farm water management practices. Given Malta’s dependence on freshwater, this study focused on outdoor field-scale irrigated production. A three staged stakeholder-driven approach was developed. The first stage included Delphi analyses to identify the key constraints on water management and fuzzy cognitive mapping to enable stakeholders to analyse their mental models and formalise conceptual and causal relationships between different components impacting on Maltese agriculture. Secondly, questionnaires were used to inform understanding of national policy gaps in water management and thirdly, a “backcasting” stakeholder workshop was used to identify policy actions to achieve a more sustainable future for agriculture on the island. The study confirmed that Malta’s core challenge is tied to poor water governance and the need to define policies that are socially and environmentally acceptable and geared to tackling the complex water challenges the agricultural sector faces. Developing support for farmer training, knowledge translation, greater public awareness of the importance and value of water for high-value crop production and multi-sector collaboration to promote shared opportunities for water infrastructure investment were highlighted as potential solutions. The findings have direct relevance to other island communities where water scarcity poses serious agronomic risks to production and where agriculture underpins rural livelihoods and the economy.
  • Integration of Biochar Filtration into Aquaponics: Effects on Particle
           Size Distribution and Turbidity Removal
    • Abstract: Publication date: Available online 26 November 2019Source: Agricultural Water ManagementAuthor(s): Zied Khiari, Kumari Alka, Stephen Kelloway, Beth Mason, Nick SavidovSmall- and large-scale biochar-based filtrations were conducted to investigate the potential of biochar as a low-cost renewable filtration medium in aquaponics. The small-scale experimental design investigated the effects of 2 biochar media sizes (1 – 3 mm [referred to as fine biochar] and 3 – 5 mm [referred to as coarse biochar]), 3 biochar bed heights (2.5, 5.0 and 10.0 cm) and 3 loading rates (5, 10 and 15 m3/m2/d) on particle size distribution as well as turbidity removal efficiency. Both biochar sizes (fine and coarse) were able to clarify fish effluent. However, fine biochar led to better filtration characteristics compared to coarse biochar. Results indicated that biochar filter bed heights and loading rates affected the filtration performances. Using deeper filters combined with lower loading rates led to greater removal of suspended particles and turbidity compared to shallower filters and/or higher loading rates. Results from the large-scale filtration, using a mixture of fine and coarse biochar media (size of 1 – 5 mm), revealed that the ideal loading rate for maximizing the removal of turbidity from fish effluent in high-intensity aquaponic system for production of Nile tilapia and greenhouse plants (with 80 m3 total volume of water, 40 kg/m3 average stocking density and 15 kg/d feeding rate) was 10 m3/m2/d. This study suggests that biochar-based filtration could be incorporated into aquaponics as a polishing step before sending the water to plant growth systems.Graphical Graphical abstract for this article
  • Bivariate analysis of drought duration and severity for irrigation
    • Abstract: Publication date: Available online 26 November 2019Source: Agricultural Water ManagementAuthor(s): L. Vergni, F. Todisco, B. Di Lena, F. MannocchiAbstractIn this study, the effectiveness of a bivariate analysis of agricultural drought characteristics for irrigation planning was evaluated. The case study was conducted in locations in central Italy and was based on olive crops which are widely grown in that area under rainfed or deficit irrigation regimes. For each locality, the available time series of daily precipitation and maximum and minimum temperatures were used to simulate the daily soil water dynamics (SWt) for olive crops. The simulation was performed assuming 10 irrigation strategies, different for both the volume and date of the interventions. By applying the Theory of Runs to SWt, with a threshold corresponding to the readily available water, the agricultural drought events in the time series were identified and characterised by their duration D (days) and severity S (i.e. the cumulative evapotranspiration deficit in mm) for each locality and strategy.A 2-parameter Gamma distribution was fitted to both D and S, whilst their dependence structure was modelled by a Gumbel copula. The evaluation of the best irrigation strategy in each locality was obtained by comparing the contour lines of the pairs (d,s) having a 10-year return period for the condition D ≥ d AND S ≥ s. Results showed a great influence of both climate and irrigation strategy on the joint distribution of D and S. Some strategies, despite a very similar behaviour in the severity, differed a lot in terms of the associated values of duration, thus denoting different dynamics of water stress (more or less intense). Among the single-irrigation strategies, the optimal one was usually represented by an application at the end of June. Among the double-irrigation strategies, the optimal one involved two interventions, one at the end of June and one at the end of July. These results were also discussed taking into account the corresponding probability of consecutive severe drought events.
  • Effects of different concentrations of dissolved oxygen or temperatures on
           the growth, photosynthesis, yield and quality of lettuce
    • Abstract: Publication date: Available online 24 November 2019Source: Agricultural Water ManagementAuthor(s): Zan Ouyang, Juncang Tian, Xinfang Yan, Hui ShenAbstractWith the continuous improvement of living standards, people pursue vegetables of higher quality, and increasing the yield and quality of vegetables has become the goal of many researchers. To accurately study the effects of different dissolved oxygen concentrations (6.5, 7.5, and 8.5 mg L−1) in the irrigation water or climatic chamber temperatures (16, 18, and 20 °C) on the growth, photosynthesis, yield and quality of lettuce (Lactuca sativa L. var. Grand Rapids Tbr), a comparative design based on a three-color light climate chamber was used. An increase in the dissolved oxygen concentration and the temperature had significant effects on the plant height, transpiration rate (E), soluble protein and nitrate contents (P
  • Rootstocks modulate the physiology and growth responses to water deficit
           and long-term recovery in grafted stone fruit trees
    • Abstract: Publication date: Available online 21 November 2019Source: Agricultural Water ManagementAuthor(s): Ismael Opazo, Guillermo Toro, Ariel Salvatierra, Claudio Pastenes, Paula PimentelAbstractThe effects of climate change have forced to search quickly new strategies to achieve sustainable agriculture in the context of a growing demand for food. Rootstocks have shown to have a key role in the resistance and tolerance to biotic and abiotic stresses in horticultural and fruit trees species, being a way to incorporate these strengths to the cultivated varieties. Here, we report the assessment of physiological parameters and growth responses of two commercial interspecific hybrid Prunus rootstocks contrasting in their tolerance to water deficit: ‘ROOTPAC®40’ (tolerant) and ‘ROOTPAC®20’ (sensitive); grafted with the almond cultivar Non Pareil or the Japanese plum cultivar Angeleno. Plants were subjected during 35 days to two irrigation treatments, well-watered and water deficit (drought period), followed by a recovery period of 44 days. On each period, biomass accumulation, stomatal density, water-use efficiency at the whole plant level and root hydraulic conductivity were determined in both irrigation treatments. Also, in the drought period, the fraction of transpirable soil water when the relative transpiration drops and the expression of seven aquaporins belonging to plasma membrane intrinsic proteins subfamily was assessed. In the drought period, ‘ROOTPAC®20’ had a decrease in the aquaporin gene expression in roots and also had an early decline in transpiration, independent of the grafted scion. Also, on this rootstock, the biomass was more severely affected. On the other hand, ‘ROOTPAC®40’ induced a late decline in transpiration and increased the water-use efficiency, keeping less affected the biomass accumulation. Contrasting with the above, in the recovery period, ‘ROOTPAC®20’ improved the water-use efficiency, reaching higher biomass accumulation in the grafted plants. Also, we observed some interesting interactions between rootstocks and scions. ‘ROOTPAC®20’ induced a higher stomatal density in both, almond and plum scions, and ‘Angeleno’ plum induced a bigger root hydraulic conductivity in both rootstocks, in comparison to almond ‘Non Pareil’, in the drought period.
  • Soil sensing technology improves application of irrigation water
    • Abstract: Publication date: Available online 20 November 2019Source: Agricultural Water ManagementAuthor(s): A.G. El-Naggar, C.B. Hedley, D. Horne, P. Roudier, B.E. ClothierAbstractDynamic irrigation scheduling for Variable-rate irrigation systems is essential to accurately estimate the spatiotemporal pattern of irrigation water requirement. Real-time, sensor-based and soil-water balance scheduling methods were compared on a trial under a Variable-rate center pivot irrigation system. The soil-water balance scheduling used the FAO56-ET model to calculate daily soil-water deficits and to determine crop water requirements using climate data from a local climate station. The sensor-based scheduling system used a wireless soil moisture sensing network to trigger irrigation when soil water deficit reached a critical value in a web-based user interface. The scheduling was conducted on pea and French bean crop trials under one center pivot, with two delineated irrigation management zones at Massey University’s No.1 Farm, Palmerston North, New Zealand.The results showed variation between the two scheduling methods where the soil water balance assumed that the soil is well drained. The sensor-based scheduling technique delivered 27–45% less water. As there were no significant crop growth and yield differences between the two approaches, irrigation-water-use efficiency was greater under the sensor-based scheduling regime. Further research is planned to assess the feasibility of including this monitoring system in a precision irrigation control system.
  • The regional water-conserving and yield-increasing characteristics and
           suitability of soil tillage practices in Northern China
    • Abstract: Publication date: 20 February 2020Source: Agricultural Water Management, Volume 228Author(s): Jialin Wang, Zhihua Pan, Feifei Pan, Di He, Yuying Pan, Guolin Han, Na Huang, Ziyuan Zhang, Wenjuan Yin, Jiale Zhang, Ruiqi Peng, Zizhong WangAbstractWater deficiency seriously restricts the agricultural production in Northern China. Soil tillage practices can conserve water and increase yield effectively, but the regional applicability of soil tillage practices has not been systematically studied so far. It is significant to study the regional characteristics of tillage practices on water-conserving and yield-increasing so that the optimal practices for improving the crop water production and maintaining the agricultural sustainable development can be determined. This study applied the meta-analysis method to analyze results extracted from 156 peer-reviewed published papers conducted at 62 agricultural experimental sites for evaluating the effects of commonly used tillage practices, i.e., No-tillage (NT), Subsoiling (SS), Mulching (M), Ridge and Furrow Planting without Mulching (F), and Ridge and Furrow Planting with Mulching (F–M) on crop yield, water consumption and water use efficiency (WUE) of wheat and maize in Northern China. The results showed that NT only increased yield of winter wheat in North-central China and spring maize in Northeast China. SS increased wheat and maize yield by 16.3 ± 3.2 % and 9.2 ± 3.0 %, and increased water consumption by 8.4 ± 3.4 % and 1.8 ± 1.8 %, respectively. M increased the yield of wheat and maize by 14.9 ± 2.9 % and 17.7 ± 6.2 %, respectively, while it did not increase the water consumption. F increased the yield of wheat by 5.0 ± 1.1 %. F–M increased wheat and maize yield by 18.9 ± 6.3 % and 36.6 ± 11.8 %, respectively. This study recommends that, SS is suitable for winter wheat and summer maize in North-central China. M and F–M are suitable for spring maize in North-central China as well as wheat and maize in Northwest and Northeast China
  • Comparison of emitters of ceramic tube and polyvinyl formal under negative
           pressure irrigation on soil water use efficiency and nutrient uptake of
           crown daisy
    • Abstract: Publication date: 20 February 2020Source: Agricultural Water Management, Volume 228Author(s): Pingguo Yang, Yun Bian, HuaiYu Long, Patrick J. DrohanAbstractThis study compared water-use efficiency (WUE) and nutrient absorption of Glebionis coronaria L. through emitters of ceramic tube (CT) and polyvinyl formal (PF) under negative pressure irrigation. Three (↓4 kPa, ↓8 kPa,  ↓12 kPa) water-supply treatments and artificial watering (CK) with pot experiments were investigated. The results showed that soil water content ranged from 18.1 to 27.2% with CT and 18.5–27.6% with PF, respectively. A decrease of water supply pressure resulted in a gradual decrease of water supply, water consumption, and nitrogen content of Glebionis coronaria L., whereas the contents of phosphorus and potassium gradually increased. The soil water content, plant height, yield, nutrient uptake, and WUE of plants irrigated with the PF emitter were superior to those irrigated with the CT emitter. The best water supply model was a water supply pressure of ↓4 kPa during the early growth stage and ↓8 kPa in the middle and late stages. Thus, water supply pressure has significant effects on the growth and development, yield, WUE, and nutrient absorption of Crown Daisy.
  • Feasibility of using pretreated swine wastewater for production of water
           spinach (Ipomoea aquatic Forsk.) in a hydroponic system
    • Abstract: Publication date: 20 February 2020Source: Agricultural Water Management, Volume 228Author(s): Entao Jin, Leipeng Cao, Shuyu Xiang, Wenguang Zhou, Roger Ruan, Yuhuan LiuBased on sufficient pollutants in pretreated swine wastewater (PSW), this study aimed to explore feasibility of growing water spinach (WS) in a hydroponic system using PSW as a liquid fertilizers in a hydroponic system. The tolerance values of WS to Cu(Ⅱ), Zn(Ⅱ), total phosphorus (TP), and ammonium-N (NH4+-N) in culture solution were found to be 0.5, 2.0, 150, and 300 mg·L−1, respectively, in the hydroponic systems. The fresh stem-leaf production of WS in undiluted PSW increased by 38.9% compared to the control group (Formula B of leafy vegetable solution culture in South China Agricultural University), and the concentration of nutrients (chlorophyll a, chlorophyll b, β-carotene, and sugar) of WS was also higher than the control group. The concentration of Pb(Ⅱ), Hg(Ⅱ), As(Ⅴ), and Cr(Ⅱ) in WS was all below the safety standard content for agriculture production in China. After 20 d hydroponic culture, the NH4+-N, TP, Cu(Ⅱ), and Zn(Ⅱ) concentration in PSW significantly decreased to 19.77 (
  • Selected soil water tensions at phenological phases and mineral content of
           trace elements in rice grains – mitigating arsenic by water management
    • Abstract: Publication date: Available online 19 November 2019Source: Agricultural Water ManagementAuthor(s): Jaqueline Trombetta da Silva, Fernanda Pollo Paniz, Fabiana e Silva Sanchez, Tatiana Pedron, Daiane Placido Torres, Fernanda Izabel Garcia da Rocha Concenço, José Maria Barbat Parfitt, Bruno Lemos BatistaAbstractThe adoption of water-saving practices in rice cultivation modifies soil water tension regime, then influencing accumulation of chemical elements in rice grains. Some studies report higher concentrations of arsenic (As) in rice grains produced in anaerobic soils, compared to those produced in aerobic soils. However, there is a lack of information about the association between water stress imposed at distinct phenological phases of rice and the accumulation of chemical elements in grains. The aim of the present work was to determine the levels of As, Cd, Co, Cu, Fe, Mg, Mn, Ni, Pb, Se and Zn in husked grains of three rice varieties cultivated under different soil water tensions, imposed at distinct phases of the development. The study was conducted during 3 years with 3 rice varieties. The higher soil water tension in vegetative phase influenced Cd accumulation, Mn, Cu and Co. The reproductive phase 1 (panicle initiation - anthesis) is the main phase regarding uptake of chemical elements, when the highest soil water tension implied the lowest As accumulation in grains concomitantly with increase of toxic elements Cd and Pb, although keeping them below the threshold levels determined by FAO/WHO, and essential elements as Mn, Zn, Se, Cu, Co and Ni. The increased soil water tension in reproductive phase 2 (anthesis - ripening) decreased the levels of Pb in BRS Pampa. There is association among the contents of chemical elements (especially Cd, As and Pb) in grains, rice variety, grain yield and irrigation scheduling, especially for As.
  • Manure application at long-term in no-till: Effects on runoff, sediment
           and nutrients losses in high rainfall events
    • Abstract: Publication date: Available online 15 November 2019Source: Agricultural Water ManagementAuthor(s): Jair Augusto Zanon, Nerilde Favaretto, Gabriel Democh Goularte, Jeferson Dieckow, Gabriel BarthAbstractManure application in agricultural systems has demonstrated improvement on physical, chemical and biological soil properties as well as on crop production, however, it may generate environmental problems, such as transport of pollutants associated with surface runoff. The aim of this work was to evaluate if the improvement on soil properties with the long-term liquid dairy manure (LDM) application can reduce the water, soil and nutrients losses by surface runoff under intense simulated rainfall. The intense simulated rainfall (60 mm h-1) was applied once before winter sowing over maize harvested residue (straw), three months after the harvest and eight months after the last application of LDM (0, 60, 120 and 180 m3 ha-1 year-1), which was continually applied on the surface mulch with no incorporation (no-till system) during twelve years, twice a year, in the summer and winter crops with three replicates. The surface runoff was evaluated up to 90 min at different time intervals and sediments, nitrogen, phosphorus, and carbon were analyzed. In general, the results indicated an increase on runoff and sediment losses and on nutrient concentrations and losses with LDM application (120 m3 ha-1 year-1). The expected positive effect on soil physical, chemical and biological properties by long-term LDM application was not enough to reduce the losses through runoff in heavy rainfall, even with the presence of straw and the absence of surface sealing (simulated rainfall was applied eight months after LDM application). However, the expected high concentration of nutrients on the soil surface increased the concentration of nutrients in runoff. The high proportion of bioavailable phosphorus indicates a major contribution on losses of readily available phosphorus for aquatic life. These results suggest the need for complementary conservation practices in no-till to prevent the input of runoff in watercourses during events of intense precipitation, even in the unmanured soil.
  • Improving water uptake by trees planted on a clayey soil and irrigated
           with low-quality water by various management means: A numerical study
    • Abstract: Publication date: Available online 15 November 2019Source: Agricultural Water ManagementAuthor(s): David Russo, Asher Laufer, Asher Bar-TalThe yield of avocado trees planted on clayey soils decreases due to irrigation with treated-waste water (TWW). We hypothesized that the main cause for this yield reduction is the reduction in water uptake by the trees roots. The aim of this numerical study was to identify the main soil factors that control the reduction in water uptake by the trees roots, and to test various soil substrate-based and water-based management schemes design to counterweigh the water uptake reduction. The study relies on physically based, three-dimensional (3-D) simulations of flow and transport in variably saturated, spatially heterogeneous, flow domain, conducted for three successive years. The main findings of this study suggest that: (i) the long-term effect of irrigation with TWW on the response of the flow system is attribute to the salinity of the TWW, and not to its sodium adsorption ratio, SAR; (ii) with respect to improving water uptake by the trees' roots, the water-based scheme that alternates irrigation water quality between TWW and desalinized water, DSW, (ADW) performed better than the water-based scheme that uses fresh water only (FW). The soil substrate-based schemes, TUFp, that used trenches with highly coarse-textured soil material and pulse irrigations, and, particularly, SAop, that used trenches with finer soil texture, performed substantially better than the soil substrate-based scheme that used trenches with highly coarse-textured soil material only (TUF); (iii) with respect to minimizing solute leaching below the root zone, the water-based schemes, FW, and, particularly, ADW, performed substantially better than the soil substrate-based schemes.Graphical abstractGraphical abstract for this article
  • A new analytical method for estimating the 3D volumetric wetting pattern
           under drip irrigation system
    • Abstract: Publication date: Available online 15 November 2019Source: Agricultural Water ManagementAuthor(s): Murat KilicAbstractThe wetting pattern and its components are important factors in the optimum design and operation of a drip irrigation system. In this investigation, the 3D volumetric wetting pattern which occurred under the surface drip irrigation was described analytically. In the laboratory experiment, the spatio-temporal variation of the wetting pattern was observed during the water application period, and the sizes of its components were measured at five-minute intervals. The components of the pattern were the wetted radius on the soil surface at any time during irrigation and the maximum wetted depth and maximum wetted width in the soil profile. In addition, camera records were taken during the experiment. Some physical and chemical features of the soil sample which were important for irrigation were analyzed. Also, the infiltration test was performed by double-ring infiltrometer in the field where the soil samples were taken. The moisture content of the soil was determined at the beginning of the irrigation application. In the next stage, the wetting pattern was located on the Coordinate System, and the main movement equations describing the spatio-temporal variation of the pattern were obtained. The volumetric wetting pattern was determined by processing these functions in the 3D system. Drip irrigation may be applied on various soil textures, with different emitter discharges and application times. Although wetting patterns in various conditions show different properties of shape from each other, the models devised contain the entire main common components of the wetting pattern. As a result, when the models were run with the data from the experiment, the 3D wetting pattern in the drip irrigation system was determined and analyzed comparatively from the points of view of main movement features of water in the soil profile and on the soil surface.
  • Optimization of furrow irrigation performance of sugarcane fields based on
           inflow and geometric parameters using WinSRFR in Southwest of Iran
    • Abstract: Publication date: Available online 14 November 2019Source: Agricultural Water ManagementAuthor(s): Reza Mazarei, Amir Soltani Mohammadi, Abd Ali Naseri, Hamed Ebrahimian, Zahra IzadpanahAbstractAccurate design, suitable management and optimization of irrigation design parameters play an important role in increasing the performance of furrow irrigation. The main objective of this study was to optimize the performance of furrow irrigation using WinSRFR in the fields of Salman Farsi Agro Industry sugarcane, located in the southwest of Iran. For this purpose, field experiments were conducted under nine blocked-ended furrows with the length of 250 m, the top width of 1.83 m and slope of 0.04 % and in three inflow treatments (1.0, 1.5 and 2.0 L/s) with three repetitions. The WinSRFR software was employed to optimize the combination of irrigation parameters such as inflow rate, cut-off time and field geometry. Objective function (OF) including application efficiency, distribution uniformity and deep percolation was also employed to optimize the performance. The results showed that using 1.0 L/s inflow rate could increase OF by 35.99 % which was the best performance compared to 1.5 and 2.0 l/s. Changing furrow length from 250 m to 200 m showed that OF value increased by 39.8.% ; however, changing it to 300 m, OF decreased by 7.7 %. In addition, changing slope from 0.04 to 0.03 % decreased OF by 0.9.%, while changing it to 0.05 % OF was improved by 1 %. On the other hand, changing the inflow and cut-off time, field length and combinations of them led to the increased OF by 25, 8.39 and 31 %, respectively. Finally, to obtain the maximum performance in sugarcane fields, inflow rate of 3 L/s and cut-off time of 379.5 min were suggested.
  • Artificial intelligence approach to estimate discharge of drip tape
           irrigation based on temperature and pressure
    • Abstract: Publication date: Available online 14 November 2019Source: Agricultural Water ManagementAuthor(s): Amin Seyedzadeh, Saman Maroufpoor, Eisa Maroufpoor, Jalal Shiri, Omid Bozorg-Haddad, Farnoosh GavaziAbstractOne of the effective factors to ensure the desirable operation of drip irrigation systems is the uniform emitter discharge, which is affected by operating pressure and temperature. Accurate estimation of this parameter is crucial for optimal irrigation system management and operation. In this research, the emitter outflow discharge was simulated through artificial intelligence (AI)-based approaches under a wide range of temperature (13−53 °C) and operating pressures (0–240 kPa) variations. The applied AI models included artificial neural networks (ANN), neuro-fuzzy sub-clustering (NF-SC), neuro-fuzzy c-Means clustering (NF-FCM), and least square support vector machine (LS-SVM). The input parameters matrix consisted of operating pressure, water temperature, discharge coefficient, pressure exponent and nominal discharge, while the ratio of measured discharge to nominal discharge (modified coefficient, M) was the output of the models. The applied models were assessed through the robust k-fold testing data scanning mode. The 5-agent Global Performance Indicator (GPI) was used for the final reliable ranking. The results showed that all the applied AI models with an average mean absolute error (MAE) of 8.8% had acceptable accuracy for estimating the modified M coefficient. According to the GPI, the LS-SVM model had the lowest error, followed by the NF-SC model with a slight difference.
  • Improving/maintaining water-use efficiency and yield of wheat by deficit
           irrigation: A global meta-analysis
    • Abstract: Publication date: Available online 14 November 2019Source: Agricultural Water ManagementAuthor(s): Liuyang Yu, Xining Zhao, Xiaodong Gao, Kadambot H.M. SiddiqueAbstractPopulation growth and climate change are necessitating increases in food production and reduction in amounts of water used for agriculture. Deficit irrigation has been proposed as a strategy to maintain/increase yield while reducing the use of water in agriculture; however, it has not been widely adopted, in part, due to risk of reduced yield. In this paper, we describe a meta-analysis designed to quantify effects of deficit irrigation on wheat water-use efficiency (WUE) and yields, and identify optimal strategies for deploying deficit irrigation to achieve win-win effects of improving WUE and yield simultaneously. Overall, the meta-analysis of 41 peer-reviewed publications collectively containing over 381 observations showed that the win-win relationship between WUE and wheat yield does exist. Overall, deficit irrigation improved wheat WUE by 6.6 % but decreased yield by 16.2 %. However, the results varied, depending on irrigation methods (such as irrigation type, timing and water amount) and environmental factors (such as precipitation, temperature and soil properties). In order to maximize win-win effects and minimize tradeoff between WUE and yield, we found that deficit irrigation is most appropriate for areas where total precipitation during the growing season is less than 200 mm and the soil is loamy or sandy. Deficit irrigation using border and furrow irrigation is more likely to achieve high WUE and yield concurrently than drip or sprinkler irrigation. Importantly, we found that the most influential factors affecting yield and WUE are the irrigation level, and the irrigation thresholds to achieve various scenarios between WUE and yield. Our findings suggest deficit irrigation can improve yield and WUE simultaneously, and identifies the conditions under which these improvements can be realized.
  • A crop coefficient –based water use model with non-uniform root
    • Abstract: Publication date: Available online 13 November 2019Source: Agricultural Water ManagementAuthor(s): Robert C. Schwartz, Alfonso Domínguez, José J. Pardo, Paul D. Colaizzi, R. Louis Baumhardt, Jourdan M. BellAbstractUncertainties in the estimation of evapotranspiration (ET1) using the crop coefficient (Kc)-reference ET method arise for deeply rooted crops and severe water stress. We expanded upon the crop coefficient–based model by modifying plant available water via a nonuniform root distribution that limited deep water extraction using daily estimated soil profile water contents. The model was calibrated to predict maize (Zea mays L.) ET over a wide range in crop water deficits. In addition, maize grain yield was calibrated with model-predicted ET using a multiplicative water production function. The calibrated model with optimized crop and stress response coefficients predicted actual maize ET for a wide range in water deficits with a daily and growing season prediction root mean square error (RMSE) of 1.16 mm d−1 and 25.6 mm, respectively. A nonuniform root distribution functioned similarly to stress response coefficients reducing soil water extraction deeper in the profile with a resultant 18% reduction in the prediction RMSE compared with the optimized stress response conventionally used with the Kc approach. The largest uncertainties in predicted crop ET resulted from an underestimation of runoff and an overestimation of crop water use during stress-induced early senescence. Measured and predicted soil water contents averaged over the entire rooting depth agreed closely, however root water extraction was overestimated deeper in the profile. Calibration of the water production function using data exhibiting a wide range in measured grain yield resulted in a RMSE of 2.1 Mg ha−1. Including an additive high temperature stress response expression improved the calibration. Because of the limited input requirements and robustness over a wide range in crop water stress levels, the model would be suitable for evaluating deficit irrigation strategies.
  • Factors affecting crop water use efficiency: A worldwide meta-analysis
    • Abstract: Publication date: 20 February 2020Source: Agricultural Water Management, Volume 228Author(s): N. Mbava, M. Mutema, R. Zengeni, H. Shimelis, V. ChaplotAbstractWater is a limiting natural resource for agricultural production. While it is well accepted that crop types differ in their water use efficiency (WUE), there is no consensus on the main factors affecting WUE of main field crops, which was the motivation of the current study. The effects of rainfall pattern, soil type and climatic regime on crop WUE were evaluated using data from 514 experiments around the world published in ISI journal papers. The results confirmed that crop type had a significant effect (p 
  • CLUES model calibration and its implications for estimating contaminant
    • Abstract: Publication date: Available online 13 November 2019Source: Agricultural Water ManagementAuthor(s): Annette Semadeni-Davies, Charlotte Jones-Todd, M.S. Srinivasan, Richard Muirhead, Alexander Elliott, Ude Shankar, Chris TannerCatchment water quality models are essential for fresh water management; however, their value is dependent on their performance and level of uncertainty and for this information to be communicated in a transparent and understandable way to key stakeholders.Here we present the latest calibration of the Catchment Landuse for Environmental Sustainability model (CLUES) and examine the implications of the calibration for estimating in-stream contaminant attenuation. CLUES estimates catchment mean annual loads of Total Nitrogen, Total Phosphorus and E. coli and is widely used in New Zealand for both catchment planning and policy development. CLUES contains three freshwater model components derived from existing water quality models. Two are based on the New Zealand Overseer and SPASMO models and have been pre-calibrated for use in CLUES. The third component is based on the USGS SPARROW model and its parameters have been calibrated against annual loads estimated from monthly water quality data from catchments across the country.We found that CLUES gives reasonable load estimates at the catchment scale (Nash-Sutcliff efficiencies> 0.8 for all the contaminants). However, there was significant uncertainty in the SPARROW parameterisation. We conclude that while CLUES can be used to estimate catchment contaminant loads, it cannot adequately estimate instream attenuation. Improved representation of lower order streams in the calibration data would allow us to evaluate the source yields from each of the model components to better estimate attenuation.Graphical abstractGraphical abstract for this article
  • Effects of treated urban wastewater irrigation on bioenergy sorghum and
           soil quality
    • Abstract: Publication date: Available online 13 November 2019Source: Agricultural Water ManagementAuthor(s): Vijayasatya N. Chaganti, Girisha Ganjegunte, Genhua Niu, April Ulery, Robert Flynn, Juan M. Enciso, Manyowa N. Meki, James R. KiniryAbstractProlonged drought in arid west Texas has resulted in freshwater scarcities in the Rio Grande basin, forcing growers to abandon agricultural lands. Augmenting freshwater scarcities with marginal quality treated urban wastewater could be an alternative strategy. However, higher salinity in wastewater could be detrimental to crops and soil quality. Therefore, developing information on crops that are salt tolerant and less water-intensive is important to sustain agriculture in this region. Sorghum is both drought and salt-tolerant and could potentially provide revenue due to increasing demand for its lignocellulosic biomass in biofuel industry. This two-year field study evaluated (i) the performance of bioenergy sorghum under wastewater irrigation in terms of its biomass yield potential and biomass quality relative to freshwater irrigation and (ii) wastewater irrigation effects on rootzone soil quality including soil salinity and sodicity. A split-plot experimental design was used with water type (fresh and wastewater) as the main-plot and soil amendments (non-amended and gypsum + sulfur) as the subplot factors. Results show that sorghum biomass yields were not significantly different between fresh and wastewaters in any of the years. Differences in biomass quality were observed overtime but as an indirect consequence of increased soil salinity and/or sodicity after wastewater irrigation. Soil quality changes were apparent with salinity and sodicity increasing over time with irrigation, but this effect was pronounced under wastewater irrigation. Application of gypsum and sulfur was able to significantly reduce soil sodicity, especially in wastewater irrigated plots. The results from this study highlight that treated wastewater can be successfully used to grow bioenergy sorghum in arid regions. However, appropriate soil management practices should be in place to counter the effects of high sodium in wastewater. These results have important implications in diversifying cropping pattern in this region while also help extend freshwater supplies through increased reuse of treated urban wastewater.
  • Differential irrigation scheduling by an automated algorithm of water
           balance tuned by capacitance-type soil moisture sensors
    • Abstract: Publication date: 20 February 2020Source: Agricultural Water Management, Volume 228Author(s): Jesús María Domínguez-Niño, Jordi Oliver-Manera, Joan Girona, Jaume CasadesúsAutomated software tools are required to undertake the routine tasks and decision-making involved in scheduling irrigation. A key issue in this topic is how to integrate sensors in the scheduling approach. The objectives of this research were to test, in the context of drip-irrigated orchards: (a) the suitability of FAO’s water balance method, locally adjusted by sensors, as the basis for the scheduling algorithm, (b) the suitability of capacitance-type soil moisture sensors, and an approach for their automated interpretation, for providing feedback to the scheduling algorithm, and (c) the performance of these combined approaches in the autonomous scheduling of irrigation in an apple orchard with heterogeneous vigour. The trial consisted of applying for two years the proposed approaches using an experimental web application, IRRIX, which scheduled irrigation of two irrigation sectors, which differed in tree size. The automated system was compared with manual scheduling by a classical water balance and with the actual evapotranspiration determined by a weighing lysimeter located in the same orchard. Results show that the irrigation applied by the automated approach in the sector of larger trees agreed with the ET determined by the lysimeter and, overall, with the scheduling by an experienced irrigator using a classical water balance. Meanwhile, as a result of a different feedback from soil moisture sensors, the same system reduced irrigation in the sector of smaller trees by a similar amount to that expected from the differences between the two sectors in the fraction of photosynthetically active radiation. This study illustrates that the method of water balance complemented with capacitance-type soil moisture sensors provides a sound basis for automated irrigation scheduling in orchards.Graphical abstractGraphical abstract for this article
  • Spring safflower water use patterns in response to preseason and in-season
           irrigation applications
    • Abstract: Publication date: 20 February 2020Source: Agricultural Water Management, Volume 228Author(s): Bishwoyog Bhattarai, Sukhbir Singh, Sangamesh V. Angadi, Sultan Begna, Rupinder Saini, Dick AuldAbstractThe deep root system of safflower (Carthamus tinctorius L.) is an important adaptive trait under rainfed conditions in semi-arid agriculture. Lower water requirements and ability to tolerate abiotic stresses make safflower a potential alternative crop for the Southern High Plains (SHP). However, information on water extraction patterns of safflower and its role in oil yield formation under center pivot irrigation system that keeps only the surface soil profile wet with frequent irrigations is limited. Therefore, a field experiment was conducted in a split-plot design at Clovis, New Mexico during 2012 and 2013 growing seasons to assess the soil water use patterns, evapotranspiration, and oil yield of two spring safflower cultivars under different preseason and in-season irrigation levels. Half of the experimental units received 164 and 153 mm of preseason irrigation in 2012 and 2013, respectively, while the other half remained unirrigated. Five in-season irrigation levels (I1–I5) ranging from 88 to 392 mm in 2012 and from 83 to 373 mm in 2013 were applied to preseason and no-preseason irrigation blocks. On average, safflower extracted 70 and 28 mm of stored soil moisture in the preseason and no-preseason irrigation treatments, which significantly increased evapotranspiration (ET), water use efficiency (WUE), and oil yield in preseason compared to no-preseason irrigation treatment. Average water extraction decreased with increasing level of in-season irrigation and a decline of 32, 27, and 25% in soil moisture at the end of the season compared to initial soil moisture were observed in I1, I3, and I5, respectively. Since, WUE was not much affected by in-season irrigation treatment in both years, limiting the in-season irrigation level to I4 can save 17% of irrigation with a corresponding 9% reduction in oil yield. The relatively smaller differences were observed for water extraction and WUE among the cultivars. Overall, safflower was able to use preseason irrigation water more efficiently in semi-arid SHP. Growers can pre-irrigate safflower and reduce its in-season irrigation to allocate more water to high water requirement traditional-crops such as corn.
  • Study on factors affecting corn yield based on the Cobb-Douglas production
    • Abstract: Publication date: 20 February 2020Source: Agricultural Water Management, Volume 228Author(s): Qichen Zhang, Weihong Dong, Chuanlei Wen, Tong LiAbstractThis paper presents an analysis of the quantitative correlations between corn yield and its influencing factors in Daqing City, China by establishing a Cobb–Douglas production function model. The effective precipitation, corn planting area and chemical fertilizer and pesticide application rates were selected as the influencing factors of corn yield. Using the Cobb–Douglas production function model, the output elasticity and degree of influence for each factor on increasing grain yield were calculated. The current fertilizer and pesticide application rates, effective precipitation and planting area had positive effects on increasing corn yield, and the Daqing City area has the potential to produce more corn. Among the four influencing factors, the amounts of pesticide applications had the greatest impact on corn yield, followed by planting area, amounts of chemical fertilizer applications and, finally, effective precipitation. In this study, we used remote-sensing images combined with meteorological station data to calculate the effective precipitation in corn fields in Daqing City. The accuracy of this method was 0.01%–11.0% greater than that of the traditional effective precipitation calculation method. The innovation was the use of Thiessen polygons to calculate regional precipitation by combining satellite images with ground meteorological station data. The insufficient sensitivity of satellite inversion for precipitation (short and heavy rainfalls cannot be detected) and insufficient temporal resolution were avoided by using precipitation data from ground meteorological stations. Using satellite image interpretations, the weight coefficient of precipitation could be confirmed according to the location and size of the study area, improving the accuracy of Thiessen polygons in calculating regional precipitation. However, this method still has limitations. When calculating precipitation over a short time, it can be limited by the cloudiness of satellite images. When calculating the long-term precipitation trend, it can be limited by incomplete precipitation data from surface meteorological stations.
  • Comparisons of spray characteristics between vertical impact and turbine
           drive sprinklers—A case study of the 50PYC and HY50 big gun-type
    • Abstract: Publication date: 20 February 2020Source: Agricultural Water Management, Volume 228Author(s): Maosheng Ge, Pute Wu, Delan Zhu, Lin ZhangAbstractVertical impact and turbine drive sprinklers are the most widely used high-volume sprinklers with both solid set spray and hose-drawn traveler irrigator systems. Different mechanical structures and driving modes between the two types of sprinklers will inevitably lead to differences in spray performance, which may affect the adaptability of each sprinkler. Thus far, there are few comparative studies that have quantitatively analyzed the spray characteristics of the two types of gun sprinklers, resulting in the lack of guidance in sprinkler-type selection for both sprinkler system designers and farmers. In this paper, the vertical impact drive gun sprinkler (50PYC) and turbine drive gun sprinkler (HY50) were used to conduct a comparative analysis of water distribution and kinetic energy distribution between these two commonly-used sprinklers. The results show that the average radial application rate of 50PYC was 11.0%–35.9% higher than that of HY50 under fixed spray conditions. Under mobile spray conditions, the water distribution of the two gun sprinklers initially increased and then decreased as the distance from the travel lane increased, exhibiting a unimodal distribution. Both the cumulative irrigation depth and average radial application rate of 50PYC were significantly higher than those of HY50 in the spray area close to the travel lane. Under overlapping spraying conditions using two adjacent sprinklers of the same type, various working pressures and different spacing between sprinklers, the maximum distribution uniformity coefficients of the 50PYC gun sprinkler reached 80.5% to 87.8%, while the maximum distribution uniformity coefficients of the HY50 gun sprinkler were approximately 67.1% to 76.9% (5.3% to 13.5% lower than that of 50PYC). Under fixed spray conditions, the peak values of spray kinetic energy of the turbine drive-HY50 was about 1.5–2.7 times that of the 50PYC gun sprinkler under different working pressures. Under mobile spray conditions, the cumulative kinetic energy in the whole spray area of the HY50 gun sprinkler was about 1.5–2.4 times that of the 50PYC gun sprinkler. This quantitative study on two common types of sprinkler guns, vertical impact and turbine drive sprinklers, indicates that to comprehensively obtain greater irrigation benefits, soil and crop types, irrigation water quality, and economic and labor costs should also be taken into consideration when selecting between the two gun sprinklers.
  • Unified framework for model-based optimal allocation of crop areas and
    • Abstract: Publication date: 20 February 2020Source: Agricultural Water Management, Volume 228Author(s): Raphael LinkerAbstractThe paper presents a model-based optimization scheme for allocation of cropping areas and water. The novelty of the scheme is that rather than using highly simplified models of crop response to deficit irrigation, detailed dynamic models of crop/soil/atmosphere interactions are used to determine the crop water productivity function. While the use of such models has traditionally been considered as prohibitive in terms of computation time, the current scheme circumvents this limitation by using each model independently in a simple multi-objective optimization procedure outside of the main optimization procedure. Once the optimization problem dealing with land and water allocation has been solved, the same models are used to compute optimal irrigation schedules for each crop at each location. During the season, a simplified version of the optimization scheme can be used to update water allocation in response to discrepancies between the actual and forecasted weather or factors such as changes in water quota or crop prices. The proposed scheme is illustrated for a hypothetical farm with four fields near Davis, CA. The model AquaCrop is used to determine optimal cropping and water allocation for simultaneous cultivation of maize and sunflower at that farm.
  • Evaluation of within-season grapevine evapotranspiration patterns and
           drivers using generalized additive models
    • Abstract: Publication date: 20 February 2020Source: Agricultural Water Management, Volume 228Author(s): Noa Ohana-Levi, Sarel Munitz, Alon Ben-Gal, Yishai NetzerAbstractEvapotranspiration (ETc) levels are influenced by the area of plant canopy, atmospheric conditions, plant physiology, and soil-water relations, which are all subjected to changes throughout the growing season. Understanding temporal trends, variability, and interactions between ETc and its governing factors is valuable for modeling, predictions and vineyard water management. Our research objective was to quantify temporal patterns of ETc of ‘Cabernet Sauvignon’ grapevines and affecting meteorological (temperature, relative humidity, radiation, wind speed) and vegetative (leaf area) factors during the growing season and within five phenological growth stages (0–4). Temporal variability of ETc was modeled using five consecutive seasons of lysimeter time-series data, capturing the non-stationary nature of the data in terms of seasonality, trends and within-seasonal patterns. The temporal dependence of ETc and its drivers throughout growing seasons was evaluated using the Box-Pierce test, autocorrelation function (ACF) and partial ACF. Patterns of the relations between ETc and its covariates were quantified using multiple nonlinear regression, the generalized additive model (GAM), at the full growing season scale and for each phenological stage. Further examination on the effect of leaf area on ETc was conducted using area under curve calculations and ETc-leaf area ratio. The results demonstrate temporal autocorrelation structure of the data, supporting the incorporation of time variables in the GAM. Each phenological stage had a unique composition of relative importance of the covariates, with variation in ETc being largely explained by time variables. Ordinarily, ETc in early season (Stage 0) and at late season (Stage 3, approaching harvest) was mostly influenced by leaf area dynamics, while in mid-season it was highly affected by temperature. The GAM enabled quantification of within-seasonal patterns of interrelations between covariates and their effects on ETc, and revealed inter-seasonal variability due to dissimilar meteorological conditions. Agro-technical management affects canopy dimensions and structure, thus influencing ETc-leaf area relations.
  • Estimation of daily potato crop evapotranspiration using three different
           machine learning algorithms and four scenarios of available meteorological
    • Abstract: Publication date: 20 February 2020Source: Agricultural Water Management, Volume 228Author(s): Sevim Seda Yamaç, Mladen TodorovicAbstractCrop evapotranspiration (ETc) is a complex and non-linear process difficult to measure and estimate accurately. This complexity can be solved applying the machine learning techniques with different meteorological input variables. This study investigated the performance of k-Nearest Neighbour (kNN), Artificial Neural Networks (ANN) and Adaptive Boosting (AdaBoost) models to predict daily potato ETc using four scenarios of available meteorological data as: air temperature (scenario 1), air temperature and solar radiation (scenario 2), air temperature, solar radiation and wind speed (scenario 3), and air temperature, solar radiation, wind speed and relative humidity (scenarios 4). The analysis was based on the results of experimental trials carried out in Southern Italy in 2009 and 2010 and focussed on the potato crop cultivation under optimal water supply. The results of ETc estimation with different machine learning techniques were compared with ETc obtained from the soil water balance model, based on the FAO Penman Monteith approach, and gravimetric measurements of soil water content in the crop root zone. The best performances were observed with the kNN model with R2 of 0.813, 0.968 and 0.965, slope of regression 0.947, 0.980 and 0.991, modelling efficiency (EF) of 0.848, 0.970 and 0.972, root mean square error (RMSE) of 0.790, 0.351 and 0.355 mm day−1, mean absolute error (MAE) of 0.563, 0.263 and 0.274 mm day−1 and mean squared error (MSE) of 0.623, 0.123 and 0.126 mm day−1 for scenarios 1, 2 and 3, respectively. When all meteorological variables were available (scenario 4), the ANN model produced slightly better statistical indicators. Therefore, the kNN model could be recommended for the estimation of ETc when limited meteorological data are available. Otherwise, the ANN model should be applied.
  • Mimicking some features of a root-soil system by dual porosity media
    • Abstract: Publication date: 20 January 2020Source: Agricultural Water Management, Volume 227Author(s): Navneet Kumar, Jaywant H. ArakeriAbstractWe report an experimental study of evaporation from a non-homogeneous dual porous system consisting of a finer pore size material at the centre surrounded by coarser particles in a glass beaker. This configuration can be considered to mimic, to a first order, the coupling between the plant roots and soil water. Similar to how roots extract water from the soils, here also water moves, driven by the capillary pressure gradient, from larger to the smaller voids. We explore two different configurations (a) when the small pore sizes span the entire porous column along the gravitational direction and (b) when they are limited to a thin annular region at the porous medium top surface. We measured the mass loss from the system, surface temperature using a thermal camera, and the ambient conditions. We compared the results with two standard systems – (a) a homogeneous porous medium and (b) a texturally layered configuration of finer particles at the top and coarser at the bottom. Compared to the homogeneous case, the duration of stage 1 (high evaporation rate regime) of evaporation and thus the characteristic evaporative length increased significantly in the case of root-mimics; this outcome shows the ability of the root-mimics in sustaining the surface water content induced by the strong capillary pressure gradient in such a dual porosity system. Finally, we track the evaporation sites using the fluorescein dye particles method and assess its effect (if any) on the overall evaporation characteristics.
  • Corrigendum to “Thermal imaging and passive reflectance sensing to
           estimate the water status and grain yield of wheat under different
           irrigation regimes” [Agric. Water Manage. 189 (2017) 98–110]
    • Abstract: Publication date: 20 February 2020Source: Agricultural Water Management, Volume 228Author(s): Salah Elsayed, Mohamed Elhoweity, Hazem H. Ibrahim, Yaser Hassan Dewir, Hussein M. Migdadi, Urs Schmidhalter
  • Selection of flow rate and irrigation duration for high performance bay
    • Abstract: Publication date: 20 February 2020Source: Agricultural Water Management, Volume 228Author(s): RJ Smith, MJ UddinAbstractThe maximum efficiency attainable by surface irrigation in any particular situation is determined largely by the soil infiltration characteristic and the flow rate onto the field. Performance evaluations have suggested that higher flow rates than those traditionally recommended can lead to increases of about 20% in the application efficiency of bay irrigation across the dairy regions of southern Australia. However, substantially reduced irrigation durations are required to realise these efficiency gains and greater precision is required in the selection and management of these shorter durations.In this paper, infiltration characteristic curves representative of the predominant (cracking and non-cracking) soils of the region are used in the surface irrigation simulation model SISCO, for a range of bay lengths and soil moisture deficits, to determine: (i) the flow rates required to achieve the maximum efficiency on the bay irrigated soils of southern Australia; and (ii) the means for real-time estimation of optimum irrigation durations. The aim is provision of guidance to irrigators seeking higher efficiency through the use of higher flow rates.Real-time estimation of optimum time to cut-off must recognise the substantial variations in infiltration within a soil type and with time due to changes in antecedent moisture content, and hence must be adaptive to the conditions prevailing at the time of any irrigation. A method for estimating time to cut-off (previously developed for furrow irrigation), is extended to the hydraulically more complex case of bay irrigation. The method is based on simple linear relationships between the advance time to a nominated point part way down the field and the time to cut-off. Its application to the management of irrigations is demonstrated using data from multiple irrigations of a single bay under varying soil moisture conditions.
  • Corrigendum to “Evaluation of wavelengths and spectral reflectance
           indices for high-throughput assessment of growth, water relations and ion
           contents of wheat irrigated with saline water” [Agric. Water Manage. 212
           (2018) 358–377]
    • Abstract: Publication date: 20 January 2020Source: Agricultural Water Management, Volume 227Author(s): Salah E. El-Hendawy, Nasser A. Al-Suhaibani, Wael M. Hassan, Yaser Hassan Dewir, Salah Elsayed, Ibrahim Al-Ashkar, Kamel A. Abdella, Urs Schmidhalter
  • Real-time energy optimization of irrigation scheduling by parallel
           multi-objective genetic algorithms
    • Abstract: Publication date: 20 January 2020Source: Agricultural Water Management, Volume 227Author(s): J.C. Alonso Campos, M.A. Jiménez-Bello, F. Martínez AlzamoraAbstractThe present work is motivated by the need to reduce the energy costs arising from the pressure demands of drip and sprinkling irrigation, compounded by the increase in the energy price in recent years. Researchers have demonstrated that proper operation of the irrigation network reduces associated pumping costs. The main challenge was to obtain the optimal operation parameters on near real-time due to the fact that the high complexity of the optimization problem requires a great computational effort. The classic approach to the problem imposes a strict fulfilment of minimum pressures as a restriction. This study, however, presents a new methodology for the reordering of irrigation scheduling, incorporating the constraint of daily volume requests for each hydrant. The methodology is capable of minimizing the cost of energy while maximizing pressures at the critical hydrants. Cost reductions of about 6–7% were reached for scenarios without pressure deficit for the case study. Greater computational efficiency was achieved by posing the problem from a multi-objective approach, on the one hand, and by establishing the parallel evaluation of the objective function, on the other. The speed-up obtained by combining a reduction in the number of function evaluations thanks to the faster convergence of the multi-objective approach and the reduction of the computational time due to the parallelization of the algorithm achieved results about 10 times faster. This improvement allowed the tool to be implemented for the daily optimization of irrigation requests.
  • Agro-environmental sustainability and financial cost of reusing
           gasfield-produced water for agricultural irrigation
    • Abstract: Publication date: 20 January 2020Source: Agricultural Water Management, Volume 227Author(s): Alban Echchelh, Tim Hess, Ruben SakrabaniProduced water (PW) is the largest by-product generated from oil and gas extraction. Currently, half of the total PW volume is managed through environmentally-controverted and costly disposal practices. In dry regions, PW could be beneficially reused to irrigate crops reducing the overexploitation of freshwater resources. However, PW quality, and particularly its high salinity, sodicity and alkalinity, create uncertainties regarding the agro-environmental sustainability and the cost of this practice. The aim of this paper was to identify potential agro-environmentally sustainable irrigation schemes with gasfield-PW in hyper-arid Qatar and to estimate their operating costs. A soil-water model was used to simulate the irrigation of sugar beet with gasfield-PW under the climatic and soil conditions occurring in northern Qatar. Different irrigation strategies combining over-irrigation, PW blending with treated sewage effluent (TSE) and PW desalination were tested in order to protect the soil and the aquifer from salinisation and sodification. The operating costs of identified agro-environmentally sustainable scenarios were estimated through a cost analysis. In the case study, the simulations indicated that using an irrigation volume up to ∼300% of the crop water needs with a blend of two-thirds PW and one-third TSE (or desalinated PW) could preserve the soil stability, crop yield and groundwater quality. The least-cost option was to reduce the irrigation amount at a little over the crop water needs and mix PW with an equivalent volume of TSE or four equivalent volumes of desalinated PW which would cost $0.26/m3 and $0.46/m3 respectively. As traditional PW disposal practices cost between $0.06–$16.67/m3, reusing PW in irrigation is thus potentially a competitive PW management strategy for O&G firms.Graphical abstractGraphical abstract for this article
  • Coping with salinity in irrigated agriculture: Crop evapotranspiration and
           water management issues
    • Abstract: Publication date: 20 January 2020Source: Agricultural Water Management, Volume 227Author(s): P.S. Minhas, Tiago B. Ramos, Alon Ben-Gal, Luis S. PereiraAbstractSoil and water salinity and associated problems are a major challenge for global food production. Strategies to cope with salinity include a better understanding of the impacts of temporal and spatial dynamics of salinity on soil water balances vis-à-vis evapotranspiration (ET) and devising optimal irrigation schedules and efficient methods. Both steady state and transient models are now available for predicting salinity effects on reduction of crop growth and means for its optimization. This paper presents a brief review on the different approaches available, focusing on the FAO56 framework for coping with the effects of soil salinity on crop ET and yields. The FAO56 approach, applied widely in soil water balance models, is commonly used to compute water requirements, including leaching needs. It adopts a daily stress coefficient (Ks) representing both water and salt stresses to adjust the crop coefficient (Kc) when it is multiplied by the grass reference ETo to obtain the actual crop ET values for saline environments (ETc act = Ks Kc ETo). The same concept is also applied to the dual Kc approach, with Ks used to adjust the basal crop coefficient (Kcb). A review on applications of Ks is presented showing that the FAO56 approach may play an interesting role in water balance computations aimed at supporting irrigation scheduling. Transient state models, through alternative formulations, provide additional solutions for quantification of the salinity build-up in the root zone. These include irrigation-induced salinity, upward movement of salts from saline ground water-table, and sodification processes. Regardless of the approach, these models are now very much capable of supporting irrigation water management in saline stress conditions. For maintaining crop growth under salinity environments, soil-crop-water management interventions consistent with site-specific conditions are then discussed. Adequateness of irrigation methods, cyclic uses of multi-salinity waters and proper irrigation scheduling are further analyzed as examples of efficient means to obviate the effects of salinity.
  • Corrigendum to “Potential of the existing and novel spectral
           reflectance indices for estimating the leaf water status and grain yield
           of spring wheat exposed to diff ;erent irrigation rates” [Agric. Water
           Manage. 217C (2019) 356-373]
    • Abstract: Publication date: 20 January 2020Source: Agricultural Water Management, Volume 227Author(s): Salah E. El-Hendawy, Nasser A. Al-Suhaibani, Salah Elsayed, Wael M. Hassan, Yaser Hassan Dewir, Yahya Refay, Kamel A. Abdella
  • Effects of subsoiling before winter wheat on water consumption
           characteristics and yield of summer maize on the North China Plain
    • Abstract: Publication date: 20 January 2020Source: Agricultural Water Management, Volume 227Author(s): Naikun Kuang, Dechong Tan, Haojie Li, Qishu Gou, Quanqi Li, Huifang HanAbstractAs an important industry for national development, summer maize production occupies a key position in China and globally. However, agricultural water consumption is becoming increasingly problematic, and global climate change and long-term traditional rotary tillage have negative effects on the soil surface layer. Subsoiling has been an effective measure to improve soil surface-layer structure and increase yield. In the present study, field experiments were conducted to compare the effects of subsoiling and rotary tillage in winter wheat and summer maize double cropping systems. Subsoiling treatments at a depth of 40 cm (S40) and 35 cm (S35), and rotary tillage at a depth of 15 cm (R15) before winter wheat planting were used, and the effects of tillage methods on soil stable infiltration rate, soil water consumption, evapotranspiration, grain yield, and crop water productivity (CWP) in summer maize growing seasons were determined. The results showed that subsoiling significantly improved soil infiltration rate. Water consumption in the subsoiling treatments increased significantly, and especially promoted the crops to utilize soil water at depths below 60 cm in the soil profile. As a result, compared with R15, kernel numbers per row and 1000–grain weight in S35 were significantly increased; therefore, both grain yield and CWP were significantly improved. Our results indicate that the S35 treatment is a reasonable subsoiling measure on the North China Plain, which can increase both summer maize grain yield and CWP in double cropping systems.
  • The value of information for the management of water resources in
           agriculture: Assessing the economic viability of new methods to schedule
    • Abstract: Publication date: 20 January 2020Source: Agricultural Water Management, Volume 227Author(s): Francesco Galioto, Parthena Chatzinikolaou, Meri Raggi, Davide ViaggiAbstractThis study develops a methodology to assess the comparative advantages of new methods to plan irrigation with respect to prevailing existing irrigation practices. The methodology consists of a comparative cost-benefit analysis based on the Value of Information approach that makes it possible to analyse whether an improvement in the information available to farmers generates economic benefits. The method is applied to the problem of comparing computer irrigation models (providing irrigation advice based on measurements, water balance models and weather predictions) and prevailing irrigation practices (at times based on soil and plant observations, or on advanced technologies) in estimating and predicting crop water requirements, in pilot experiments located in four different European regions. The results reveal that the introduction of the alternative method improves the performance of irrigation practices in Mediterranean regions that are characterised by high weather variability and for those crops for which the consequences of failing to meet predictions are relatively low (i.e. tomato instead of maize, drip irrigated crops instead of sprinkler irrigated crops). Under favourable conditions, the use of the alternative technology generates a 0–20% increase in gross margin and a 10–30% water saving with respect to prevailing existing irrigation practices. The study concludes by addressing the conditions that justify the use of advanced information systems to schedule irrigation interventions and by offering some policy recommendations to drive their uptake. These include subsidising research at the evaluation stage and public investments aimed at knowledge creation (weather and shallow water table monitoring stations) and knowledge sharing (counselling) at the adoption stage.
  • Improvement of pressure chamber protocols - Response to Hochberg (2019)
    • Abstract: Publication date: 20 January 2020Source: Agricultural Water Management, Volume 227Author(s): Alexander D. Levin
  • Chemical composition of table olive wastewater and its relationship with
           the bio-fortifying capacity of tomato (Solanum lycopersicum L.) plants
    • Abstract: Publication date: 20 January 2020Source: Agricultural Water Management, Volume 227Author(s): Berta de los Santos, Eduardo Medina, Manuel Brenes, Ana Aguado, Pedro García, Concepción RomeroRecently, the potential use as fertilizer of some wastewaters from table olive factories has been reported but the cause of this activity has not been disclosed up to now. In this study, a huge number of table olive waste solutions were analyzed from three consecutive seasons. Sugars, phenolic and mineral compounds were the main chemical groups identified. The individual effect of these components was tested on the growth of tomato plants and the quality of their fruits. Two factorial designs were assayed (24 and 23), in which the individual groups of chemical substances were sugars, minerals (nitrogen, potassium and phosphor), simple and polymeric phenols. Also, fresh wash water from Spanish-style green table olive processing was tested. The main conclusion was that no one individual group caused the fertilizer activity but a synergetic action of all of them was efficient and the fresh waste solution tested was the most effective.Graphical abstractGraphical abstract for this article
  • Aquaponics using saline groundwater: Effect of adding microelements to
           fish wastewater on the growth of Swiss chard (Beta vulgaris L. spp. cicla)
    • Abstract: Publication date: 20 January 2020Source: Agricultural Water Management, Volume 227Author(s): Emi Kaburagi, Mina Yamada, Takashi Baba, Hideyasu Fujiyama, Bernardo Murillo-Amador, Satoshi YamadaAbstractSaline soil and saline groundwater reduce agricultural productivity on drylands. We are developing a new aquaponics system to improve food productivity on such lands while effectively utilizing saline groundwater. In this study, cultivation of Swiss chard (Beta vulgaris L. spp. cicla cv. Seiyou Shirokuki) was carried out using fish wastewater with a high salt concentration (1150 mg L−1 NaCl). The levels of microelements (e.g., Fe, Mn, Zn, and Cu) in the fish wastewater were very low, so we added microelements at 100% (W100), 50% (W50), 25% (W25), and 0% (W0) of the levels in the standard hydroponics solution to the fish wastewater and investigated the effects on growth of Swiss chard. At the first harvest, yields in all wastewater treatments were as high or higher than in the control. At the second harvest, yields in W100, W50, and W25 were not significantly different from the control, while in W0 the yield was significantly lower and chlorosis was evident. At the third harvest, the yield in all wastewater treatments was less than in the control, and chlorosis symptoms were observed in W25 and W0. Since leaf Mn and Zn concentrations in W25 and W0 had decreased to below the critical values for those microelements, Mn and Zn deficiency might have contributed to the observed chlorosis and yield loss. For the cultivation of Swiss chard with fish wastewater, sufficient yield (i.e., comparable to or better than the control) without chlorosis was obtained when microelements were added at 50% of the level of the control solution. In addition, since sufficient yield was obtained even in W0 at the first harvest, it is suggested that longer-term cultivation and higher yield could be achieved by applying 50% microelements after the first harvest.
  • Optimizing fertilization under ridge-furrow rainfall harvesting system to
           improve foxtail millet yield and water use in a semiarid region, China
    • Abstract: Publication date: 20 January 2020Source: Agricultural Water Management, Volume 227Author(s): Xudong Zhang, Muhammad Kamran, Fangjian Li, Xuanke Xue, Zhikuan Jia, Qingfang HanAbstractEffects on the soil water and foxtail millet yield of different fertilizer rates coupled with the ridge-furrow rainfall harvesting system (RFRHS) are unclear, which could guide improvements to productivity in dryland farming. We conducted field experiments using RFRHS and traditional flat planting (TFP) at four different fertilizer rates: (i) no fertilizer (CK); (ii) low (L), N 90+P2O5 60 kg ha–1; (iii) medium (M), N 180+P2O5 120 kg ha–1; and (iv) high (H), N 270+P2O5 180 kg ha–1. RFRHS significantly improved the topsoil water content (by 4.7–8.5% in 0–40 cm layer) and topsoil temperature (by 0.4–0.7 °C), which stimulated stable seedling establishment and accelerated millet growth. Fertilization significantly enhanced water absorption in 0–140 cm profile, prolonged the growth period of millet and significantly increased dry matter accumulation. Finally, under RFRHS, the grain yield and water use efficiency (WUE) of foxtail millet increased by 6.2% and 6.7%, respectively, compared with TFP, and they tended to increase more as fertilizer rate increases, indicating a positive interaction between water and nutrients. However, under RFRHS, the M fertilizer rate obtained a higher yield (average 6748.6 kg ha–1), WUE (average 18.6 kg ha–1 mm–1) compared with CK and L rates, and made a greater contribution to the grain yield (average 32.1%), but no further significant increases were observed with the H fertilizer rate where RFRFS showed a tendency to decrease grain yield compared to TFP in wet years. Therefore, RFRHS with fertilizer application at a rate of N 180+P2O5 120 kg ha–1 may be suitable for high-efficiency farming management to improve the yield and WUE for foxtail millet in this semiarid region.
  • Facilitating protocols while maintaining accuracy in grapevine pressure
           chamber measurements- comments on Levin 2019
    • Abstract: Publication date: 20 January 2020Source: Agricultural Water Management, Volume 227Author(s): Uri Hochberg
  • Estimation of maize yield by assimilating biomass and canopy cover derived
           from hyperspectral data into the AquaCrop model
    • Abstract: Publication date: 20 January 2020Source: Agricultural Water Management, Volume 227Author(s): Xiuliang Jin, Zhenhai Li, Haikuan Feng, Zhibin Ren, Shaokun LiAbstractThe accurate and timely estimation of temporal and spatial changes in crop growth and yield before harvesting is essential for ensuring global food security. The integration of remote sensing data and crop models is a potential approach for the estimation of key crop growth parameters and crop yields. Therefore, the aim of this study was to assimilate biomass and canopy cover (CC) derived from vegetation indices into the AquaCrop model using the particle swarm optimization (PSO) algorithm in order to obtain a more accurate estimation of CC, biomass, and yield for maize. The results show that, compared to other vegetation indices, the enhanced vegetation index (EVI) and the three-band water index (TBWI) can be used to obtain a better estimation of CC (R2 = 0.78 and root-mean-square error (RMSE) =9.84%) and biomass (R2 = 0.76 and RMSE = 2.84 ton/ha), respectively. Additionally, it was found that the data assimilation approaches in which only CC was used as a state variable (scheme SVcc) and only biomass was used as a state variable (scheme SVbio) can be used to obtain more accurate estimations of CC (R2 = 0.83 and RMSE = 8.12%) and biomass (R2 = 0.81 and RMSE = 2.51 ton/ha), respectively; however, larger differences were found between the measured and estimated values of one variable (i.e., CC or biomass) when the other variable (i.e., biomass or CC) was used as the only state variable during the data assimilation. The data assimilation approach in which both CC and biomass were used as state variables (scheme SVcc+bio) produced a robust result, with the estimation accuracy being fairly close to that obtained using the single-variable (SVcc or SVbio) data assimilation approaches. The estimation accuracy for maize yield was slightly better when using a double-variable data assimilation approach (R2 = 0.78 and RMSE = 1.44 ton/ha) than when using a single-variable data assimilation approach. In summary, this study presents a robust approach for increasing the estimation accuracy for maize CC, biomass, and yield, and for optimizing field management strategies, by assimilating remote sensing data into the AquaCrop model at a regional scale.
  • How can terracing impact on soil moisture variation in China' A
    • Abstract: Publication date: 20 January 2020Source: Agricultural Water Management, Volume 227Author(s): Die Chen, Wei Wei, Liding ChenAbstractSoil moisture plays a key role in vegetation restoration and ecosystem stability. Terracing modulates hydrological processes by lowering the slope gradient and shortening the slope length. The response of soil moisture variation to terracing is strongly influenced by land use, climate, topography and terracing characteristics. In this study, we conducted a meta-analysis to examine the response of soil moisture to terracing in China. For China’s landscapes, terracing generally improved the soil moisture by 12.9%. Relative to other terracing structures, level ditches showed the greatest water conservation benefits, especially on steep slopes. Terracing had higher water storage benefits in the northern plains and the southern dry-hot valleys of China. The benefits of water storage by terracing rose with increasing slope gradients above 15° and fell with increasing depth of soil layers. Soil moisture in the 0–100 cm depth differed among terracing structures but not among land uses, mainly due to the differences in evapotranspiration under different micro-topographical conditions. In contrast, soil moisture at the depth of 100–200 cm differed among land use types but not among terracing structures, only because root water uptake always differed across land use types. Regarding climatic factors, precipitation played a dominant role in soil moisture variation.
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