苜蓿生产力动态及其水分生态环境效应

根据长期田间试验实测数据 ,分析了苜蓿人工草地鲜草产量水平 ,产量随生长年限的变化 ,以及产草量和降水量的关系 ;苜蓿对肥料的敏感性较低 ,但肥料有延长苜蓿经济性生长年限的功能 ;水量平衡法计算苜蓿耗水量时 ,土层计算深度具有重要意义。当采用2m和 1 0m两种不同计算深度时 ,所得耗水量差值巨大 ,特别是在揭露水分生态环境演变趋势上 ,会得到不同结论。 1 0m测深研究结果表明 ,在黄土高原 ,苜蓿草地年蒸散量大于年降水量 ,根系吸水层达 1 0m以下 ,多年连续种植会导致土壤干燥化 ,形成生物性土壤下伏干层 ,从而对陆地水分循环路径发生影响。据此提出黄土高原草地生产要改高产目标为适度生产力目标 ,以减缓或阻止下伏干层的形成 ,并提出了相应的农业技术措施。

PRODUCTIVITY DYNAMIC OF ALFALFA AND ITS EFFECTS ON WATER ECO-ENVIRONMENT

The emphasis of this study is laid on effect of alfalfa growth on soil water eco environment based on data obtained from actual measurements in a long term experiment. At first,yield of fresh alfalfa and its change with the growth life,and the relationship between grass yield and precipitation were analysed. Then,the significance of measuring soil water at depth for calculating consumption and revealing effects of alfalfa on water eco environment were presented. Difference in calculating soil depth resultsed in different conclusions in analysis of effects on water eco environment. It pointed out that in the Loess Plateau the annual consumption is more than the annual precipitation for alfalfa which has deep roots more than 10 meters. Therefore continual growth of alfalfa can lead to desiccation and form a desiccative layer below the upper soil layer,which affects the way of water cycle on land. It is concluded that in order to slow down or prevent formation of the drying layer an appropriate productivity goal of grassland should be set and relevant agricultural technological measures are proposed.