عنوان مقاله [English]
Introduction:Water scarcity, improper management of water resources, excessive application of chemical inputs, and lack of proper cultivation patterns are present in agriculture. Lack of attention to these cases will inflict irreparable damage on the agricultural sector. Accordingly, attention to sustainable agriculture, conservation of water resources and prevention of improper use of chemical fertilizers are essential to reduce environmental pollution. In many cases, there is agreement on the river basin scale as a suitable spatial scale for analysis of water resources management. Tajan Basin with area of about 4187 km2 is one of the important parts of Caspian Sea Basin. The Current status of water resources in Tajan basin due to decrease in river runoff, has doubled the focus on the basin's water resources management.
Materials and Methods: In this study, with the help of positive mathematical planning and maximum entropy approach in GAMS, policies to reduce the use of chemical fertilizers and water in selecting the appropriate cultivation pattern for 2017 in the Tajan basin were reviewed. Within the model, the farmer maximizes the expected utility of their stochastic income, subject to resource and non-negativity constraints. To include both market and yields uncertainty, we calculated profit covariance matrices by using national averages for prices and yields for the 2018–2009 period. The resource constraints include land, water and fertilizer. Selected irrigated crops in the region include rice, wheat, rapeseed and corn. In the present study for simulating farmers' response, reduction scenarios including 5%, 10% and 15% of available water and fertilizer are considered. There are also two environmental sustainability index that are related to amount of the used fertilizer and water. The smaller the index is, the greater sustainability is provided in crop production.
Results and Discussion: Calibration of PMP pattern with maximum entropy approach showed that there is no difference between the value of target function, inputs and cultivation level in the current situation and calibration pattern. In all water reduction scenarios, the total cultivation area decreased. The results indicate that the agriculture in the basin is vulnerable due to changes in available water. The 15% decrease in water resources causes a significant decrease of 15/903% of the cultivation area. Cultivation area under fertilizer reduction scenarios has been lower in comparison with water scenarios, and so reduces the used fertilizer and increases soil conservation and water stock. In reduction scenarios of water and fertilizer, land reallocation is reduced due to less reduction in expected utility of farmers. In water scarcity conditions and lack of fertilizer, rice and wheat crops have higher economic benefits per hectare than other crops. The sustainability index for used fertilizer in all reduction scenarios of water and fertilizer is lower than the current pattern. Also the index of the used water in the PMP model is lower than the baseline in the region that decrease was 0.018%, 0.144% and 0.319% at three levels of 5%, 10% and 15%, respectively. In the scenario of 15% reduction of fertilizer, land allocation and economic benefits decreased by 13.83% and 0.034%, respectively. However used fertilizer and water index improved to 1.348% and 0.319%, respectively. Therefore, improving the water and fertilizer application index has a higher priority than reducing the expected utility in the region.
Conclusion: In the current cropping pattern, farmers do not pay attention to the environmental characteristics and sustainability of the region. While with the policies of reducing the quantity and price of chemical inputs and introducing different types of sustainability indicators, it is possible to develop a cultivation model. In addition to earning the necessary profit, it enables the optimal use of fertilizer and water inputs. Changing the behavior of farmers compared to the current pattern of input consumption requires strong motivation and reasons. Therefore, water quality tests and soil decomposition in the region, as well as providing appropriate formulas for optimal use of chemical fertilizers is needed. Extension services to increase people's awareness is a good solution for optimal use of inputs and increase the level of cultivation and farmers' profits.