linear programming

water over-withdrawal in Iran is like a cancer that has taken root in the country's nature and is making its conditions difficult every day. Therefore, planning and effective measures must be taken at the country level to reduce this over- withdrawal. For this purpose, in the present study, it was assumed that withdrawal water for agriculture in the country would decrease from 86 billion m3 per year to 62 billion m3 per year (the allocable volume of water for agriculture as announced by the Ministry of Energy). Then, using linear programming, the current cropping pattern was optimized with the aim of maximizing farmers' income. In this study, information on the cultivated area, yield per unit area, price and production cost (2013-2017) of more than 30 important plant species was collected separately for each province of the country. To estimate the irrigation water volumes under farmers’ conditions, a crop simulation model (SSM-iCrop2) was used, which has been tested and set up to simulate the growth, yield and field water balance for more than 30 plant species throughout the country. The economic mathematical programming model was solved using LINGO software. The results showed that reducing water withdrawal from 86 to 62 billion m3 per year without changing the cropping pattern would cause the country's irrigated area to decrease by 29 percent (from 8,409 to 5,949 thousand hectares) and farmers' income would also decrease by 30 percent (from 173 to 121 thousand billion rials). However, the optimization of the cropping pattern resulted in an 18% reduction in the cultivated area (from 8,409 to 6,907 thousand hectares) and an increase in farmers' income by 9% (from 173 to 190 thousand billion rials); that is, while water withdrawal decreased by 28%, farmers' income not only did not decrease but also increased with the optimization of the cropping pattern. The optimized cropping pattern also created significant savings in fertilizer and energy consumption, which is of great importance in conditions of limited energy resources. The most important changes in the optimized cropping pattern were the increase in the cultivated area and production of potato and summer vegetables (104 and 76 percent more than the country's needs, respectively) that must be exported, and the decrease in the cultivated area, production, and consequently increased dependence on imports in sugar-beet, barley, silage corn, and alfalfa. In the optimized cropping pattern, high dependency (more than 50%) to import of oilseeds, grain corn, and meal will continue as in the current conditions (current cropping pattern). Optimization of the cropping pattern makes it possible to reduce water withdrawal to the level that the Ministry of Energy without reducing farmers' income. However, there will still be some reduction in the area under irrigated cultivation and, as a result, a decrease in the self-sufficiency of some crops. Thus, the expectations of the country's crop production capacity must be rationalized and reduced.

Choosing the optimal cultivation model that is both environmentally sustainable and suitable for specific climatic conditions in each geographical region can be considered as one of the efficient solutions to solve the challenges and increase the profitability of agricultural activities.For this purpose, in this study, an attempt has been made to design the optimal pattern of crop cultivation in Miandoab plain, which is the fourth most important plain of the country, located in West Azarbaijan province.Optimizing the cultivation pattern was done in the form of two separate goals of maximizing profit and minimizing water consumption.For this purpose, the required data for the three years 2016-2018 were collected from various provincial and national institutions, and the average data of the mentioned three years were used to propose the optimal pattern of crop cultivation in the form of each of the mentioned goals.In this research, 12 important crops cultivated in this plain have been used.The results showed that the two crops of rainfed chickpeas and nut sunflowers, with the cultivation of the entire agricultural lands of the plain with approximately 57 thousand hectares and 5500 hectares, respectively, and a gross profit of 1614 billion rials, were introduced as the optimal model proposed with the aim of maximizing the gross profit.became.In the proposed cultivation model with the aim of minimizing water consumption, the re-cultivation of rainfed chickpeas and nut sunflowers on an area equal to 57.600 hectares and 5300 hectares will result in the optimization of water consumption.In other words, two goals of profit maximization and water consumption minimization will be achieved by sub-cultivating dry peas and sunflower seeds.