EFFECTS OF IRRIGATION AMOUNT ON ALFALFA YIELD AND QUALITY WITH A CENTER-PIVOT SYSTEM

Irrigation amount is one of the most important factors that need to be considered in the management of center-pivot irrigation systems for alfalfa producers. In 2014 and 2015, a field study was conducted at Saiwusu, Inner Mongolia, China. Three irrigation levels (100%, 80%, 60% ET) were used to evaluate the effects of irrigation amount on alfalfa yield and quality. For assessing the effects of water distribution variation of center-pivot systems on alfalfa yield and quality, the water application depth, alfalfa yield, and quality between the first span, second span, overhang, and end gun were also compared. The results showed no significant difference in annual yield between the 100% and 80% ET irrigation levels. Compared to irrigation at 100% and 80% ET, irrigation at 60% ET caused significant reductions in yield of 10% and 11%, respectively. As the irrigation amount decreased, total crop water use significantly declined from 617 to 405 mm, and water use efficiency (WUE) increased from 21.8 to 29.8 kg ha(-1) mm(-1). The water production functions of alfalfa were parabolic for each harvest. The proportions of seasonal actual water applied to each cutting were approximately 25%, 32%, and 43%, with contributions to annual yield accounting for 54%, 30%, and 16%, respectively, indicating that the third harvest of alfalfa had great potential for improving WUE and saving water. Irrigation level had a noticeable effect on the relative feed value (RFV) but no effect on crude protein (CP) concentration. The 60% ET irrigation level was conductive to increased CP concentration and RFV of alfalfa but was of no help to improve alfalfa quality grade. The spatial distributions of annual yield and quality were highly related to the spatial distribution of water for the center-pivot system. The coefficients of variation (CVs) for annual yield, RFV, and CP of the whole system were 5% to 12%, 2% to 8%, and 1% to 8%, respectively, while the CVs for actual irrigation amount ranged from 11% to 13%. Over-irrigation caused by the end gun slightly increased alfalfa annual yield, but it reduced the quality and WUE. Therefore, the end gun in a center-pivot irrigation system should be carefully selected for improving the uniformity of water application. The 80% ET irrigation level in the first and second cuttings and the 60% ET irrigation level in the third cutting are recommended for alfalfa production in semi-arid regions, such as western Inner Mongolia in China.