On quantifying soil water deficit of a partially wetted root zone by the response of canopy or leaf conductance |
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| Institution: | 1. Xinjiang Institute of Ecology and Geography, CAS, 40-3 South Beijing Road, Urumqi, Xinjiang 830011, PR China;2. Department of Environmental Physics and Irrigation, Volcani Center (ARO), Ministry of Agriculture, Bet Dagan 50250, Israel;3. Department of Soil and Water, Faculty of Agriculture, Hebrew University of Jerusalem, Rehovot 76100, Israel;1. Institute of Applied Ecology, Chinese Academy of Sciences, Shenyang 110016, China;2. Ministry of Agriculture Key Laboratory of Crop Nutrition and Fertilization, Institute of Agricultural Resources and Regional Planning, Chinese Academy of Agricultural Sciences, Beijing 100081, China;3. State Key Laboratory of Soil and Sustainable Agriculture, Institute of Soil Sciences, Chinese Academy of Sciences, Nanjing 210008, China;4. Centre for Carbon, Water and Food, School of Life and Environmental Sciences, The University of Sydney, Camden, NSW, 2570, Australia;1. State Key Laboratory of Soil and Sustainable Agriculture, Institute of Soil Science, Chinese Academy of Sciences, Nanjing 210008, Jiangsu Province, China;2. University of the Chinese Academy of Sciences, Beijing, China;1. State key laboratory of hydrology-water resources and hydraulic engineering, Hohai University, Nanjing 210098, China;2. College of water conservancy and hydropower engineering, Hohai University, Nanjing 210098, China;3. Water conservancy bureau of Kunshan, Kunshan 215300, China;1. The United Graduate School of Agricultural Science, Tokyo University of Agriculture and Technology, Fuchu, Tokyo 183-8509, Japan;2. The Graduate School of Agriculture, Tokyo University of Agriculture and Technology, Fuchu, Tokyo 183-8509, Japan;3. The Graduate School of Fisheries Science and Environmental Studies, Nagasaki University, Nagasaki, Nagasaki 852-8521, Japan;4. Institute of Agriculture, Tokyo University of Agriculture and Technology, Fuchu, Tokyo 183-8509, Japan;1. Institute of Resources and Environmental Sciences, School of Metallurgy, Northeastern University, Shenyang, 110819, China;2. Guangdong Key Laboratory of Agro-environmental Pollution Control and Management, Guangdong Institute of Eco-environmental Science & Technology, Guangzhou, 510650, China;3. State Key Laboratory of Urban and Regional Ecology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing, 100085, China;4. Key Laboratory of Forest Ecology and Management, Institute of Applied Ecology, Chinese Academy of Sciences, Shenyang, 110016, China |
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| Abstract: | Quantifying the soil water deficit (SWD) and its relation to canopy or leaf conductance is essential for application of the Penman–Monteith equation to water-stressed plants. As the water uptake of a single root depends on the water content of the soil in its immediate vicinity, the non-uniform distribution of water and roots in the soil profile does not allow simple quantification of SWD from soil-based measurements. Using measurements of stem sap flux (with a heat pulse technique), soil evaporation (with micro-lysimeters) and meteorological parameters the canopy conductance was obtained through inversion of the Penman–Monteith equation. SWD was evaluated by averaging the soil water content profile of the root zone (monitored by layers with the TDR sensors) weighted by root distribution of the layers. The average canopy conductance at midday (11:00–15:00, Israel Summer Time), denoted as Gnoon, was computed for each day of the experimental period. Stable summer weather, typical of the Mediterranean region, and the fully developed crop canopy, made water stress the only plausible cause of a Gnoon decline. However, the daily decline of Gnoon did not occur at the same weighted average soil water content during the successive drying cycles. For the cycle with less irrigation, the decline in Gnoon occurred at higher soil moisture levels. Alternatively, when SWD was determined from the water balance, i.e., by defining water deficit as irrigation minus accumulated evapotranspiration, the Gnoon decline occurred at the same value of water deficit for all irrigation cycles. We conclude that a climate-based soil water balance model is a better means of quantifying SWD than a solely soil-based measurement. |
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