Population growth, along with crisis of shortage and preserving the natural resources, have forced governments to adopt the policies in order to optimize the use of natural resources and to preserve them against the damaging effects of chemical materials. The purpose of this study is to investigate the different effects of reducing the amount of available water and increasing the price of agricultural inputs (fertilizer and water) on crop pattern, using Positive Mathematical Programming based on maximum entropy. The data was collected by 250 questionnaires, in cropping season 2011-12 from farmers in the Khomein plain. The results showed that the estimated model "PMP" reproduces the amounts of the base year very well. The adopted policies of increasing the costs of water and fertilizer, have led to reduction of the variety of crop pattern. The amounts of index of diversity cropping pattern (EI) of farms smaller than 5 (ha) are respectively: 0.49 and 0.60 and for farms bigger than 5 (ha) are respectively; 0.7 and 0.7751. According to the results; the adoption of two policies of reducing water availability and increasing prices simultaneously, considering a Supportive policy from the government to offset the costs imposed on farmers, is recommended as an appropriate policy in order to manage the usage of water and fertilizer.

JEL Classification: Q15, C6

Keywords:
Cropping Pattern, Positive Mathematical Programming, Maximum Entropy, Khomein Plain