Investigating virtual water content and agricultural water productivity indicators in crops (Case study: Dehloran County, Ilam Province)

Introduction
Due to the limited water resources in Iran, optimal utilization of water resources is necessary to achieve food security and sustainable development of the agricultural sector. One of the suitable solutions for the optimal use of water resources is to estimate the virtual water content and the physical and economic water productivity of agricultural products. Virtual water is the amount of water that an agricultural product consumes during the production process to reach the stage of evolution, and its amount is equivalent to the total amount of water consumed in the different stages of the production chain from the beginning to the end. The amount of virtual water required to produce a product differs according to climatic, cultural, management, and planning conditions in each country and even region. This issue makes it necessary to study the estimation of virtual water content in each region. In recent years, many types of research have been conducted to estimate the virtual water content and the physical and economic productivity of water in crops. Dehloran County is the main hub of agricultural production in Ilam Province. So far, no study has been conducted in the field of estimating the virtual water content of crops in this county. This study was therefore conducted to estimate virtual water content and physical and economic water productivity of crops (i.e., wheat, barley, maize, rapeseed, tomato, cucumber, carrot, melon, watermelon, and sesame) of Dehloran County.
 
Materials and Methods
The Dehloran County, located in the south of Ilam Province, with 6229 km² constitutes about one-third of the total area of Ilam Province. This county has 103000 ha of suitable agricultural land, of which 67000 ha are irrigated and 36000 ha are rainfed, and it is considered the agricultural hub of Ilam Province. Most of the irrigated area in the study area is devoted to cultivating crops such as wheat, barley, maize, rapeseed, tomato, cucumber, watermelon, melon, sesame, and carrot. This study investigated the virtual water content and the physical and economic water productivity of these crops in the agricultural year 2021-2022. The virtual water content of crops was estimated from the sum of green, blue, gray, and white virtual water. This study used the FAO Penman-Monteith and USDA methods in CROPWAT 8.0 software to estimate reference crop evapotranspiration and effective rainfall. Crop yields, nitrogen fertilizer consumption rates, production costs, and sales prices of crops were obtained from the Agricultural Jihad of Dehloran County. To check the validity of the mentioned data, an interview was conducted with the farmers of Dehloran County. The results of the interview confirmed the validity of the data. According to the data obtained from the water resources affairs of Dehloran County, the irrigation efficiency is equal to 85%, which was used to estimate the gross irrigation requirement. Crop per drop (CPD), benefit per drop (BPD), net benefit per drop (NBPD), and unit virtual water value (UWV) indicators were used to estimate the physical and economic water productivity of crops.
 
Results and Discussion
The results showed that the virtual water content of wheat, barley, rapeseed, maize, watermelon, melon, sesame, tomato, cucumber, and carrot crops is equal to 1.82, 1.64, 3.90, 1.49, 0.31, 0.29, 6.99, 0.49, 0.30, and 0.35 m³ kg^-1, respectively. The amount of physical water productivity (CPD index) of wheat, barley, rapeseed, maize, watermelon, melon, sesame, tomato, cucumber, and carrot products is equal to 1.53, 2.04, 0.63, 0.81, 4.17, 5.45, 0.22, 2.59, 5.45, and 3.94 kg m^-3, respectively. The amount of BPD index of wheat, barley, rapeseed, maize, watermelon, melon, sesame, tomato, cucumber, and carrot crops is equal to 0.17, 0.19, 0.14, 0.09, 0.13, 0.16, 0.10, 0.09, 0.19, and 0.12 million rials m^-3, respectively. The amount of NBPD index of wheat, barley, rapeseed, maize, watermelon, melon, sesame, tomato, cucumber, and carrot crops is equal to 0.06, 0.09, 0.04, 0.06, 0.07, 0.05, 0.10, 0.04, 0.11, and 0.07 million rials m^-3, respectively. The amount of UWV index of wheat, barley, rapeseed, maize, watermelon, melon, sesame, tomato, cucumber, and carrot crops is equal to 0.06, 0.06, 0.06, 0.08, 0.10, 0.10, 0.06, 0.07, 0.12, and 0.09 rials m^-3, respectively. According to the CPD index, cucumber, melon, watermelon, carrot, and tomato crops are respectively placed in the first to fourth priorities for cultivation. According to the BPD index, cucumber, barley, wheat, melon, and rapeseed crops are placed in the first to fourth priorities for cultivation. According to the NBPD index, cucumber, sesame, barley, watermelon, and carrot crops are placed in the first to fourth priorities for cultivation. According to the UWV index, cucumber, melon, watermelon, carrot, and maize crops are placed in the first to fourth priorities for cultivation.
 
Conclusion
Examining the amount of CPD, BPD, NBPD, and UWV indicators of the studied crops shows that cucumber has the highest physical and economic water productivity compared to other studied crops and its cultivation in Dehloran County reduces water consumption and implies high economic benefits for farmers. Melon has the lowest virtual water content and the highest physical water productivity compared to other studied crops. However, the high cost of melon production has caused this crop to not have high water economic productivity. Therefore, it is necessary to adopt supportive policies from the government to reduce production costs and increase the relative advantage of this crop. Sesame has the lowest yield and the highest virtual water content compared to other studied crops. Sesame is placed in the last priority of cultivation based on the CPD index. However, the low cost of production and high income of sesame has caused this crop to be the second priority for cultivation based on the NBPD index. The high NBPD index of sesame necessitates the need to focus on indicators that are effective in increasing the yield of sesame. Rapeseed has the second rank in terms of low yield and high virtual water content among the studied crops. Rapeseed has been placed in the eighth priority for cultivation based on the CPD index. In addition, according to the NBPD index, rapeseed has been placed in the last priority of cultivation compared to other studied crops. Therefore, it is recommended to remove this crop from the cultivation pattern of Dehloran County and replace it by planting crops with high economic productivity and low water requirements.