The objective of the work is to determine economically optimal irrigation requirement assuming the profit maximum (minimum loss). The task was to find the value of irrigation requirement which enables to get maximal profit at irrigative lands taking into account the costs of irrigation. In other words maximum yield within economical optimum has to be equal the ratio of additional costs per the unit of resource used (cost of water) to the additional income from sale of the product unit (purchase price). As a result of calculation following conclusions were made: optimal area always corresponds to the available irrigation fund; fixed costs and the costs which do not depend on irrigation requirements have no impact on the choice of economically optimal irrigation requirement; economically optimal irrigation requirement increases together with the growth of purchase price and falls down with the growth of prime cost of irrigation water; there is such an irrigation requirement below which the profit turns into loss. To determine economically substantiated irrigation requirement and rates which correspond to the minimal decrease of net profit under the reduced irrigation rates, the system of scenario study was proposed where as a managing parameter was the volume of water intake in distributor canal. Production function of the site is built which is a reflection of the net profit growth depending on water intake in distributor canal. It can further be used as initial information for solving the problem of optimal distribution of water intake to the irrigation system between sites hanged to the distributor canals assuming the requirement of maximum summary net profit from sites.
Keywords: irrigation requirement, net profit, production function, scenario study, analysis of solution stability, irrigation system, volume of water intake.
