The Distribution Characteristics Of Humus And Nutrients In Soil Aggregates Under Different Vegetations

Soil aggregates can be used as the carrier of soil organic matter, nitrogen, phosphorus, potassium and other nutrients, it makes a big difference to soil physical and chemical properties. In this article we combined field investigation and laboratory analysis methods together to study the construction of ecological environment and vegetation reconstruction in Mountain Forest-Arid Valley Ecotone of upper reaches of Minjiang River. We choose the natural secondary forest, shrub land, acacia wood land, mixed and young forest, Minjiang cypress young forest and Abandoned Lands young forest as the objects to study the composition of soil aggregates and make sure the distribution characteristics of Humus, nitrogen, phosphorus, potassium in soil aggregates under different vegetations, and in order to make sure the soil’s structure and fertility status, and provide basic theory for returning farmland to forest and ecological environment reconstruction. The main results showed that:(1) The contents of soil aggregates are dominated by>2 mm aggregates under different vegetations (nearly 60%), the difference between>2 mm and other particle size aggregates is significant. As the decreasing of aggregates’particle size, the content of soil dried aggregates decreased first and then increased, the content of 0.5-0.25mm aggregates is the lowest. As the depth of soil increasing, the content of different particle size aggregates does not show obvious regularity.(2) The contents of humus and its components in soil dried aggregates in natural secondary forest and shrub land are the highest, as the decreasing of aggregates’particle size it does not show obvious regularity, the overall performance is the contents of humus and its components in <1mm aggregates are higher than that in>lmm aggregates. Except shrub land, acacia wood land, mixed and young forest, the degree of humifications of>2mm aggregates and<0.5mm aggregates are higher, but which of middle particle size aggregates are lower.(3) The contents of nitrogen and phosphorus in soil dried aggregates in natural secondary forest are the highest, but which in acacia woodland are the lowest, the content of potassium in shrub land is the highest, but which in Abandoned Lands young forest is the lowest, as the decreasing of aggregates’ particle size it does not show obvious regularity, the overall performance is the contents of nitrogen phosphorus and potassium in<1mm aggregates are higher than that in>1mm aggregates. As the depth of soil increasing, the content of nitrogen and phosphorus in soil dried aggregates decreased under different vegetation types, but the content of potassium increased.(4) Each particle size aggregates on soil nitrogen, phosphorus and potassium’ contribution rate sorting as:larger than 5mm> 5-2mm> 2～1mm>1～0.5mm and smaller than 0.25mm> 0.5～0.25mm aggregates, the contribution rate about 46-60% comes from>2mm aggregates.(5) The contents of CEC in soil dried aggregates in Minjiang cypress young forest is the highest, but which in shrub land is the lowest, it does not show obvious regularity under different vegetation types as the decreasing of aggregates’particle size, the overall performance is the contents of CEC in<1mm aggregates are higher than that in>lmm aggregates. As the depth of soil increasing, the contents of CEC in soil dried aggregates do not show obvious regularity in natural secondary forest, but which increased in Abandoned Lands young forest and other vegetation types decreased.(6) The content of exchangeable K+ in soil dried aggregates in acacia wood land is the highest but which in Minjiang cypress young forest is the lowest, the content of exchangeable Na+ in soil dried aggregates in Abandoned Lands young forest is the highest but which in natural secondary forest is the lowest, and it does not show obvious regularity as the decreasing of aggregates’particle size. Except the content of exchangeable Na+in soil dried aggregates in natural secondary forest shows the>lmm aggregates are higher than <1mm aggregates, the overall performance is the contents of exchangeable K+ and Na+ in <1mm aggregates are higher than that in>1mm aggregates. The contents of exchangeable Ca2+ and Mg2+ in Abandoned Lands young forest are the highest and which in shrub land are the lowest. The content of exchangeable Ca2+ and Mg2+ in 2～1mm and 1～0.5mm soil dried aggregates were the lowest but which in other particle size aggregates were the highest as the decreasing of aggregates’ particle size.(7) The Base Saturation of soil dried aggregates do not show obvious regularity as the decreasing of aggregates’ particle size under different vegetations. The contribution rate of soil dried aggregates to exchangeable K+, Na+, Ca2+, Mg2+ about 53～63% come from>2mm aggregates, this mainly due to the contents of >2mm aggregates were the largest.