黄土高原半干旱偏旱区苜蓿-粮食轮作土壤水分恢复效应

Effects of alfalfa-grain rotation on soil moisture restoration in semi-arid and drought-inclined areas of the Loess Plateau

该文测定和分析了黄土高原半干旱偏旱区不同生长年限苜蓿草地以及轮作不同年限粮食作物后0～1000cm深层土壤水分变化规律。结果表明:随着苜蓿生长年限的延长,苜蓿草地土壤干层厚度逐渐增加,3年生苜蓿草地土壤干层深度达到760cm,6、7、10年生苜蓿草地土壤干层深度均超过1000cm,6年生苜蓿地1000～1500cm土层仍为干燥层,土壤平均湿度为9.68%;采用草粮轮作能明显减小苜蓿草地干层的厚度和范围,0～1000cm土壤水分较10年生苜蓿草地都有不同程度的恢复,轮作2、6、8、12和18a粮田平均土壤水分恢复速率25.2mm/a,年均累积恢复土层厚度123.1cm,0～300cm土层水分恢复程度较高,且轮作年限愈长,土壤水分恢复效果越好,轮作18a粮食作物后0～660cm土层土壤水分恢复量达到了531.1mm;苜蓿草地适宜翻耕年限为5～6a,且6年生苜蓿草地0～1000cm土壤水分恢复到当地土壤稳定湿度值需要23.8a,该地区适宜的苜蓿-粮食轮作模式为"5～6年生苜蓿→24年粮食作物"。

Soil moistures were measured and analyzed in 0- 1000 cm layers on alfalfa grasslands with different growth years and alfalfa-grain crop rotations by different growth years, in semi-arid and drought-inclined areas of the Loess Plateau. The results showed that with the increasing alfalfa growth years, the thickness of dry soil layer of alfalfa grasslands deepened gradually. The dry layer soil depth of 3 years alfalfa field had reached 760 cm, that of 6, 7, 10 years alfalfa fields had been over 1000 cm, the soil layers of 1000-5000 cm of 6 years alfalfa field were still in drying layer, the average of soil moisture was 9.68%. Alfalfa-grain crop rotation could significantly reduce the thickness and distribution of dry soil layer. Comparing with 10 years old alfalfa field, the soil moisture in 0-1000 cm profile of rotated grain crop fields had recovered in some extent. The average rate of soil water resumption was 25.2 mm per year for 2, 6, 8, 12 and 18 years grain crop rotation fields, and annual accumulative resumption in 0-1000 cm soil layer was 123.1 cm. The soil recovery degree in 0-300 cm layers was better than that in deeper soil layers, and with the extension of the rotation period, the effect of soil water resumption could be much better, the water resumption amount in 0-660 cm had reached 531.1 mm for 18 years grain crop rotation field. The suitable year for alfalfa fields to begin grain rotation was 5 or 6 years, and years for soil moisture restored to the local soil stable moisture with grain crop rotation needed 23.8 years in 0-1000 cm profile of 6 years alfalfa field. In this region, reasonable alfalfa-grain crop rotation pattern was 5 or 6 years alfalfa and 24 years grain crop planting.