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经对宁夏南部半湿润偏旱、半干旱和干旱三个类型区人工苜蓿生长状况调查,其土壤水分特征是:(1)土壤含水量随苜蓿年限延长而成直线减少,分2个时段:1～6年为y_1=9.26-0.42x_1,7～12年为y_2=7.55-0.11x_2,斜率比值为3.82。(2)土壤水分剖面干燥分为4个阶段:1～2年的土壤水分只利用到2～2.5米深,年度耗水量412～549.6毫米;3～4年土壤吸水层已延深到5米,年度耗水量431～599.2毫米;5～6年土壤耗水量达到最大值,为500～630毫米;7年以后下降,0～5米土层为414.4～528.5毫米,略高于当地降水量。(3)剖面水分利用:0～5米全亏缺,6米基本亏缺,7～8米大部分亏缺,9米部分亏缺,10米基本不亏缺。0～5米亏缺量占总数的73.1％。0～9米占96.9％。用水深度9～9.2米。(4)不同类型区土壤水分利用:随降雨增多而增大,于是,干旱区苜蓿干旱时间偏早。(5)苜蓿产量和土壤水分利用基本成正态分布。和水分效率变化相同。经分析,在干旱区的倒茬时间以6～7年为宜,半干旱地区8～9年轮作一次,半湿润地区可延长到9～10年。
The investigation of the growth of artificial alfalfa in three types of semi-humid, semi-arid and arid areas in southern Ningxia showed that: (1) The soil moisture content decreased linearly with the increase of alfalfa’s duration, and was divided into two periods: 1 ~ 6 years for y_1 = 9.26-0.42x_1, 7 ~ 12 years for y_2 = 7.55-0.11x_2, slope ratio of 3.82. (2) Drying of soil moisture profile is divided into four stages: soil moisture in 1 ~ 2 years is only used to 2 ~ 2.5 meters deep and annual water consumption is 412 ~ 549.6 mm; soil water absorbing layer in 3 ~ 4 years has been deepened to 5 meters , Annual water consumption 431 ~ 599.2 mm; 5-6 years soil water consumption reached the maximum value for the 500 ~ 630 mm; 7 years after the decline, 0 ~ 5 meters of soil 414.4 ~ 528.5 mm, slightly higher than the local precipitation. (3) Profile water use: 0 ~ 5 m full deficit, 6 m basic deficit, 7 to 8 m most of the deficit, 9 m part of the deficit, 10 m basically no shortage. 0 to 5 meters deficit accounted for 73.1% of the total. 0 ~ 9 meters accounted for 96.9%. Water depth of 9 to 9.2 meters. (4) Soil water use in different types of area: with the increase of rainfall, the drought time of alfalfa in arid area is earlier. (5) Alfalfa yield and soil water use basically became normal distribution. And the same change in water efficiency. According to the analysis, the time of stubble in arid area is 6 ~ 7 years, the rotation in 8 ~ 9 years in semi-arid area and the extension in 9 ~ 10 years in semi-humid area.