元谋干热河谷地区不同造林树种对土壤的改良作用研究

经过４年多的林木培育，元谋干热河谷地区的土壤有了不同程度的改良，其中，改良作用较大的树种是山毛豆、新银合欢、苏门答腊金合欢，土壤有机质、全氮、速效氮等指标比对照林地提高了１倍。马占相思枯落物量大，营养元素含量多，但不易分解，土壤改良效果不如其它豆科植物；赤桉的枯落物最少，是一个消耗地力的树种，在金沙江干热河谷地区的植被恢复和长江中上游防护林体系建设中应十分重视营造混交林。

Effects of Some Tree Species on Soil in Yuanmou Hot and Dry Valley

Soil in the hot and dry valley in Yuanmou was improved to some degree by growing trees for four years. Among planted tree species, improvement effect of Tephrosia candida, lencaephala, Acacia glauca on soil is better than other tree species. Organic matter, total nitrogen, hydrolysable in test fields were increased one time as much as those of control field.Improvement effect of Acacia mang uim on soil is poorer as its leaves is thicker and bigger, though it has the largest quantity of litter leaves and highest content of nutrition elements. Improvement effect of Ecalyptus camaldulensis on soil is the poorest and its quantity of litter leaves is also the smallest. Great attention should be paid to mixed forest in system of the Yangzi River shelterbelt in the hot and dry valley in Yuanmou Mixed forest is favourable to increasing imput of preciptation to plantation and improving soil, as well as to raising the ability of reserving water and providing water to soil. Establishing mixed forests is essential to maintain steady and vigorous growth of trees in the areas.