宁南山区紫花苜蓿(Medicago sativa)土壤干层水分动态及草粮轮作恢复效应

Moisture dynamics of soil dry layer and water-restoring effects of alfalfa (Medicago sativa)-grain crop rotation on soil dry layer in alfalfa farmlands in Mountainous Region of Southern Ningxia

以各类作物农田水分为对照，连续两年对宁南山区不同生长年限苜蓿深层土壤水分以及10年生苜蓿地耕翻后轮作不同年份作物农田的水分进行了测定。结果表明，随着苜蓿生长年限的增加，干层深度与厚度先增加后减小。3年生苜蓿干层深度为720cm，6年生干层最深可达1000cm以下，10年生干层深度为920cm，3—12年生苜蓿地0—700cm土层基本上均属于土壤干层范围。苜蓿地0—800cm土壤湿度随生长年限增加而降低，2004年测定的4、7年生和12年生苜蓿地0—700cm土层平均含水率分别为5．30％、5．22％和5．01％；2005年测定的3、6年生和10年生苜蓿地0—800cm土层湿度分别为6．26％、5．60％和5．27％；而800～1000cm土层湿度在一定年限后有恢复趋势。300cm为苜蓿地降水下渗的最大临界深度，300cm以下土壤干层一旦形成，将长期存在，7—12年生苜蓿300～700cm土层湿度仅维持在4．0％左右。苜蓿地和农田的土壤干层厚度与湿度有较大差异，草粮轮作可使苜蓿土壤干层水分基本恢复到农田湿度，而且轮作年份越长，土壤各层次水分恢复效果越好，10年生苜蓿轮作18年后土壤水分基本恢复到农田状态。

In two consecutive years, the study measured the soil water contents in the farmlands on which alfalfa had grown for different periods and the soil water contents in the farmland on which alfalfa had grown for ten years and then rotated with other crops in different years and then compared the soil water contents with those in different croplands. The study indicated that while alfalfa growth was prolonged the depth and thickness of soil dry layer firstly increased and then declined. The depth of soil dry layer was 720cm in the farmland with alfalfa growing for three years , at most 1000cm in the farmland with alfalfa growing for six years , and 920cm in the farmland with alfalfa growing for ten years and soil dry layer spanned nearly 0 - 700cm soil in the farmlands with alfalfa growing for 3 - 12 year. In alfalfa farmlands, the Average humilities declined in 0 - 800cm soil as the growth of alfalfa was prolonged. In 2004, the average soil water contents were measured to be 5.30% ,5.22% and 5.01% 0-700cm soil in the farmlands, with alfalfa growing for 4, 7 and 12 year, respectively; in 2005, the soil humidities were measured to be 6.26% ,5.60% and 5.27% in 0-800cm soil in farmlands with alfalfa growing for 3,6 and 10 year, respectively; But the soil humidities tended to rebound in 800 - 1000cm after alfalfa grew for a certain period. 300cm is the maximum soil depth to which the rainwater could infiltrate down, and thus soil dry layer , tended to stay permanently once it formed in soil below 300 cmm deep. , the soil humidity remained only 4. 0% in 300-700cm soil in the farmlands with alfalfa growing for 7 - 12 year. the thickness and humidities of Soil dry layer differed greatly between alfalfa farmland and cropland, but alfalfa-crop rotation made the soil humidities of soil dry layer recover to those of the croplands and its such effect was intensified in different soil layers as the rotation was prolonged .. furthermore, the 18 year alfalfa-crop rotation made the farmland with alfalfa growing for 18 years recover its soil water content to that of cropland.