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.