AbstractThe present study was carried out to evaluate two crop water production models for estimating the effects of irrigation uniformity on alfalfa hay yields. The models included the ratio of actual to maximum hay yield, two parameters of the sprinkler water uniformity, and the ratio of gross to required irrigation. Measured data from three experimental plots of a farm located in Varamin, Iran, were used for the evaluation of the proposed models. Comparisons showed that the results from both models were in good agreement with experimental results. However, the results obtained from the normal water distribution model were more accurate than those from the uniform water distribution model. The higher predictive accuracy of the normal distribution model may be due to the fact that it follows a normal pattern in terms of irrigation distribution and crop yield. The accuracy of models in estimating alfalfa hay yield improved with an increasing uniformity coefficient. The results indicate that the optimum gross to required irrigation depth ratio decreases with increasing sprinkler water uniformity value. The findings demonstrate the importance of economic constraints in determining the optimum irrigation amount. It was further found that the optimum irrigation depth increased with increasing value of the product to irrigation cost ratio. The results illustrate that normal and uniform models overestimate and underestimate the values of hay yield compared to measured values, respectively. The average difference in the yield estimation compared to measured data was 130 kg ha−1 for the uniform distribution model and 87 kg ha−1 for the normal distribution model. The average alfalfa hay yield over growing period was estimated at 24 400 kg ha−1 for the ranges of CUch between 80 and 90% in the study region. Copyright © 2008 John Wiley & Sons, Ltd.