an economic evaluation of supplemental irrigation at optimum rate of nitrogen on wheat in rainfed condition

in order to obtain the maximum benefit, yield increasing and its stability a supplemental irrigation field experiment was conducted as split plot arranged in a randomized complete block design (rcbd) with three replications during 1999-2002 at maragheh agricultural research station of dari. the treatments included four levels of irrigation (average of three years: 0, 95, 151 and 207 mm) as main plots and five n rates (0, 30, 60, 90 and 120 kg.n.ha-1) as sub plots, was carried out on rainfed wheat variety (sabalan). data analysed by partial budgeting, marginal benefit - cost ratio (bbcr), different states of water and irrigation prices, income functions and senario analysis of water productivities. optimal level of supplemental irrigation was 95 mm water use combined with 60 kg.n.ha-1 resulted maximum water productivity (20.1 kg.mm-1). in spite of 20% reduction of yield in this treatment, maximum net benefit was obtained along with probability of 180% cropping area increasing which can be led to 74% increasing in total production grain yield. limit of benefitability for optimum level of supplemental irrigation was determined as 2857 rial.m-3.