Predicting alfalfa hay production as related to water distribution functions

Abstract

The 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 À1 for the uniform distribution model and 87 kg ha À1 for the normal distribution model. The average alfalfa hay yield over growing period was estimated at 24 400 kg ha À1 for the ranges of CU ch between 80 and 90% in the study region. RÉ SUMÉLa présente étude est menée pour évaluer deux modèles de production irriguée destinés à estimer les effets de l'uniformité de l'irrigation sur les productions de foin de luzerne. Les modèles incluent le ratio entre production réelle et maximum de foin, deux paramètres de l'uniformité d'arrosage par aspersion et du ratio entre irrigation nécessaire et maximum. Les données mesurées sur trois parcelles expérimentales d'une ferme située en Varamin, Iran, ont été utilisées pour l'évaluation des modèles proposés. Les comparaisons ont montré que les résultats des deux modèles sont en accord avec les résultats expérimentaux. Pourtant, les résultats obtenus avec le modèle de distribution normal sont plus exacts que ceux du modèle de distribution uniforme. La meilleure prédiction du modèle de distribution normale peut être due au fait qu'il suit une courbe normale pour la distribution d'eau et le rendement. L'exactitude des modèles dans l'estimation de la production de foin de luzerne augmente avec le coefficient d'uniformité. Les résultats indiquent que le ratio sur le niveau d'irrigation augmente avec l'uniformité. Les conclusions démontrent l'importance des contraintes économiques dans la détermination de la quantit...

Effect of non-uniform sprinkler irrigation and plant density on simulated maize yield

“…In this way, considering irrigation distribution was able to improve model predictions of average maize yield within an irrigated field. The results of Montazar et al (2010) in alfalfa support our finding, as they concluded that alfalfa forage production was better predicted using a normal distribution of irrigation water, as compared with simulations with a uniform amount of water applied, that tended to overpredict alfalfa yield. The accurate predictions in the present experiment indicate that daily simulation of the water balance and its consequences on maize yield was crucial to…”