Quantifying Medicago sativa Yield under Deficit Irrigation Technique in Sandy Soil

Deficit irrigation technique was introduced to find the best means to conserve irrigation water in arid lands. The most common model describing deficit irrigation is water yield response model. The main advantage of such model is that it can predict relative yield drop, which arises from relative water deficit, in order to maximize the economic return. The disadvantage of the model is that it uses evapotranspiration (ET), estimated by using meteorological data, which affects the applicability of the model when there is no weather station near the field. Furthermore, the sudden changes of weather parameters and the differences of the areas covered with green plant at different growth stages might also, affect the model applicability. Therefore, the research objectives were suggesting a modified version of FAO model, using soil moisture data instead of meteorological data to provide greater accuracy and applicability and validating the proposed model. Pot experiment was conducted to achieve these objectives. Four levels of soil available water were chosen to irrigate five cultivars of Medicago sativa (as one of the most important grazing crops) cultivated in two different soils (un-reclaimed). The results showed positive linear correlation between available soil water and crop yield at all the experimental treatments. Regression equations were developed to predict crop yield resulting from water deficit. The study indicated that the maximum yield is not necessarily the optimal one to maximize the profit in arid lands. The study recommended the modified model to predict yield drop and water saving and also, presented guidelines for water management of other similar plants grown in arid lands.