林地与农地转换过程中红壤有机碳、氮和磷库的演变

通过比较自然林地、农地和造林地红壤表土不同粒级团聚体中有机碳、氮和磷的组成及分布特点,探讨林地开垦为农地和农地退耕还林过程中土壤养分的变化机理。结果表明:林地开垦为农地后,有机碳(特别是颗粒状有机碳)和全氮明显下降,有机碳的下降程度高于全氮,有机磷向无机磷转化。自然林地土壤有机碳平均比农地土壤高出219%,土壤总氮平均比农地高出15%。而当农地退耕还林后,有机碳、氮和磷呈相反的变化。自然林地、农地和造林地土壤的平均颗粒状有机碳分别占土壤总有机碳的65%,11%和47%,差异很大,大团聚体中颗粒状有机碳和有机磷的稳定性较低,最易受土地利用方式的改变而改变。表5参14

Changes of organic C,N and P pools in red soil in transformation between agricultural land and forestry land

Physical fractionation and chemical-analysis were used to assess the composition and distribution of organic C,N and P in different sizes of water-stable aggregates of red soil under different land uses.The change mechanism of soil nutrients in transformation between forestry land and agricultural land was analyzed.The27soil samples were collected for testing and were divided into three groups:natural forest land,agricultural land and afforested land.The results showed:that forest clearing and continuous cultivation for upland led to significant depletion of total soil organic C and N,and led to transform of organic P into inorganic P in surface soil.The decline of organic C was more than that of N in the soil.Organic C and total N content in natural forest land were3.19and1.15times more than those in agricultural land respectively.The proportions of particulate organic C to total C in natural forest land,agricultural land and afforested land were65%,11%and47%,respectively.The change of land use has great influence on the contents of particulate organic C and organic P in the>1mm aggregates.Ch,5tab.14ref.]