Evaluation of Spatial Crop Water Use Efficiency in Khorasan Razavi Province

IntroductionWater scarcity is the main challenging issue in supplying sufficient food in arid and semiarid regions. Agricultural production in Razavi Khorasan, like other arid and semiarid provinces, depends on underground water. Groundwater exploitation alongside climate change has dramatic effects on the availability of surface water for agricultural production in semiarid areas. Crop water use estimation is the first step to increasing Water Use Efficiency (WUE). From the water resource point of view, assessing the gap between actual and attainable crops, WUE is so important, especially for future mitigation strategies. The term water use efficiency refers to production per unit of water used by evapotranspiration, with units such as kg grain/ha per mm water or kg/m3 water, so it does not scale in the 0-1 range. This paper aims to evaluate WUE for main crops (wheat, barley, sugar beet, onion, potato, tomato, cucumber, and watermelon) in the different areas of Razavi Khorasan province (Torbat-e Heydarieh, Torbat-e Jam, Chenaran, Mashhad, Sabzevar, Quchan, Kashmar, Gonabad, and Neyshabour) for 26 years (1985-2010). Material and MethodsWUE shows crop production per unit of water use. It was calculated as production per unit of crop water used (CWU) by evapotranspiration. CWU was acquired by estimating two components: reference evapotranspiration (ETo) and crop coefficient. ETo was calculated via the Blaney-Criddle equation. Although this method has a coarse accuracy in comparison to other methods, this is ideal when only air-temperature datasets are available. We examined the relationship between yield and CWU, as well as WUE and CWU for wheat, tomato, alfalfa, and sugar beet. A polynomial line was fitted to describe the best relation between two variables. The maximum yield at each point of CWU was determined as the highest attainable yield. Mann-Kendall test was applied to detect the trend of data over time.Results and DiscussionThe long-term average of WUE showed a similar trend for wheat and barley. The highest wheat WUE was about 0.59 and 0.53 yield per m3 in Torbat-e Jam and Chenaran. Chenaran and Torbat-e Heydarieh had the highest WUE of sugar beet (3.12 and 3.08 kg fresh root per m3). The highest amount of potato WUE (4.05), tomato WUE (4.7), and onion WUE (4.9) were found in Torbat-e Jam, Chenaran, and Chenaran, respectively. Kashmar, Gonabad, and Sabzevar had the lowest WUE for most of the crops. It seems that high temperature during crop growth caused a decrease in WUE in the mentioned locations. WUE of all crops had an intense fluctuation between 1986 and 1996, while it modified in the later years to the extent that a mild increasing slope was found in WUE.A polynomial line was fitted to show yield and WUE changes, then the upper boundary line and the lower boundary line were fitted to represent attainable yield and WUE and minimum yield and WUE. The highest yields were obtained around 540, 880, 940, and 850 mm water use for wheat, alfalfa, sugar beet, and tomato, respectively and the law of diminishing returns was observed between yield and CWU. An increase in temperature caused yield and WUE to decrease. The upper boundary line was more resistant to environmental changes, whereas the lower boundary line was sensitive.The effect of 1 and 2  temperature rise on yield and WUE  was negligible, while with a three  increase, yield and WUE of lower boundary line decreased by 20%. Although a three ℃ increase in temperature had a negligible impact on WUE in the higher boundary line, WUE in the lower boundary line decreased dramatically. Alfalfa was known as the most sensitive, and sugar beet was the most tolerant crop to temperature in terms of WUE.ConclusionWUE was negatively associated with mean annual temperature rise. The results indicated that global warming damages yield stability. Yield and CWU showed a positive correlation up to the maximum yield; then, excessive CWU increases led to yield decline. When temperature increases and environmental conditions become worse, appropriate agronomic management such as changing sowing date, balancing crop nutrition, and proper irrigation schemes can play an effective role in enhancing yield. We concluded that when temperature increase, the WUEIntroductionWater scarcity is the main challenging issue in supplying sufficient food in arid and semiarid regions. Agricultural production in Razavi Khorasan, like other arid and semiarid provinces, depends on underground water. Groundwater exploitation alongside climate change has dramatic effects on the availability of surface water for agricultural production in semiarid areas. Crop water use estimation is the first step to increasing Water Use Efficiency (WUE). From the water resource point of view, assessing the gap between actual and attainable crops, WUE is so important, especially for future mitigation strategies. The term water use efficiency refers to production per unit of water used by evapotranspiration, with units such as kg grain/ha per mm water or kg/m3 water, so it does not scale in the 0-1 range. This paper aims to evaluate WUE for main crops (wheat, barley, sugar beet, onion, potato, tomato, cucumber, and watermelon) in the different areas of Razavi Khorasan province (Torbat-e Heydarieh, Torbat-e Jam, Chenaran, Mashhad, Sabzevar, Quchan, Kashmar, Gonabad, and Neyshabour) for 26 years (1985-2010).Material and MethodsWUE shows crop production per unit of water use. It was calculated as production per unit of crop water used (CWU) by evapotranspiration. CWU was acquired by estimating two components: reference evapotranspiration (ETo) and crop coefficient. ETo was calculated via the Blaney-Criddle equation. Although this method has a coarse accuracy in comparison to other methods, this is ideal when only air-temperature datasets are available. We examined the relationship between yield and CWU, as well as WUE and CWU for wheat, tomato, alfalfa, and sugar beet. A polynomial line was fitted to describe the best relation between two variables. The maximum yield at each point of CWU was determined as the highest attainable yield. Mann-Kendall test was applied to detect the trend of data over time. Results and DiscussionThe long-term average of WUE showed a similar trend for wheat and barley. The highest wheat WUE was about 0.59 and 0.53 yield per m3 in Torbat-e Jam and Chenaran. Chenaran and Torbat-e Heydarieh had the highest WUE of sugar beet (3.12 and 3.08 kg fresh root per m3). The highest amount of potato WUE (4.05), tomato WUE (4.7), and onion WUE (4.9) were found in Torbat-e Jam, Chenaran, and Chenaran, respectively. Kashmar, Gonabad, and Sabzevar had the lowest WUE for most of the crops. It seems that high temperature during crop growth caused a decrease in WUE in the mentioned locations. WUE of all crops had an intense fluctuation between 1986 and 1996, while it modified in the later years to the extent that a mild increasing slope was found in WUE.A polynomial line was fitted to show yield and WUE changes, then the upper boundary line and the lower boundary line were fitted to represent attainable yield and WUE and minimum yield and WUE. The highest yields were obtained around 540, 880, 940, and 850 mm water use for wheat, alfalfa, sugar beet, and tomato, respectively and the law of diminishing returns was observed between yield and CWU. An increase in temperature caused yield and WUE to decrease. The upper boundary line was more resistant to environmental changes, whereas the lower boundary line was sensitive.The effect of 1 and 2  temperature rise on yield and WUE  was negligible, while with a three  increase, yield and WUE of lower boundary line decreased by 20%. Although a three ℃ increase in temperature had a negligible impact on WUE in the higher boundary line, WUE in the lower boundary line decreased dramatically. Alfalfa was known as the most sensitive, and sugar beet was the most tolerant crop to temperature in terms of WUE. ConclusionWUE was negatively associated with mean annual temperature rise. The results indicated that global warming damages yield stability. Yield and CWU showed a positive correlation up to the maximum yield; then, excessive CWU increases led to yield decline. When temperature increases and environmental conditions become worse, appropriate agronomic management such as changing sowing date, balancing crop nutrition, and proper irrigation schemes can play an effective role in enhancing yield. We concluded that when temperature increase, the WUE gap will widen, and agronomic management will play a more important role in this condition. gap will widen, and agronomic management will play a more important role in this condition.