A field experiment was conducted for the purpose of examining the effects of different combinations of water and fertilizer applications on the water consumption and yields of alfalfa under subsurface drip irrigation (SDI). The results showed that the jointing and branching stages were the key stages for alfalfa water requirement. The water consumption had varied greatly (from 130 to 170 mm) during the growth period of each alfalfa crop. The water consumption during the whole growth period was approximately 500 mm, and the maximum water consumption intensity was 3.64 mm·d^-1. The overall changes in water consumption and yields during the growth period of the alfalfa displayed trends of first increasing and then decreasing. The sensitivities of the yields to water changes were much higher than that of fertilizer. The water use efficiency (WUE) of the alfalfa was determined to range from 1.68 to 3.20 kg·m^-3, and the rate of growth had ranged from 4.85% to 51.77%. The WUE and rate of growth of the alfalfa indicated the following trend: second crop > third crop > first crop. The results of frequency analysis based on the water-nitrogen-yield regression equation are the following: irrigation amounts of 142~165 mm and nitrogen application of 61~80 kg·hm^-2 have a 95% probability of obtaining a hay yield of alfalfa of more than 11903 kg·hm^-2. These results suggest that SDI is a promising irrigation method, which can increase the WUE and hay yield of alfalfa under the condition of SDI within an appropriate amount of water and nitrogen fertilizer, and too low or too high water and nitrogen fertilizer will adversely affect the WUE and hay yield of alfalfa.

中文翻译：

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不同水肥条件下地下滴灌对紫花苜蓿耗水量和产量的影响

进行了田间试验，目的是研究地下滴灌条件下不同水肥组合对紫花苜蓿耗水量和产量的影响。结果表明，拔节和分枝阶段是苜蓿需水的关键阶段。在每种苜蓿作物的生长期，其耗水量变化很大（从130毫米到170毫米）。整个生育期的耗水量约为500 mm，最大耗水强度为3.64 mm·d ^-1。紫花苜蓿生长期水耗和产量的总体变化呈现出先增加后减少的趋势。产量对水变化的敏感性比肥料高得多。紫花苜蓿的水分利用效率（WUE）确定为1.68至3.20 kg·m ^-3，生长速率为4.85％至51.77％。苜蓿的水分利用效率和增长率表明以下趋势：第二季>第三季>第一季。根据水-氮-产量回归方程进行频率分析的结果如下：灌溉量为142〜165 mm，施氮量为61〜80 kg·hm ^-2，具有95％的概率获得苜蓿干草超过11903 kg·hm ^-2。这些结果表明，SDI是一种很有前途的灌溉方法，在适量的水和氮肥条件下，SDI可以增加苜蓿的水分利用效率和干草产量，而过低或过高的水和氮肥都会对苜蓿产生不利影响。苜蓿的水分利用效率和干草产量。