Soil Carbon and Nitrogen Concentration under Different Land Use in Central Hilly Area of Hunan Province

A comparative study was made of the vertical distribution characteristics of soil carbon and nitrogen contents of forest plantation,economic forest-land,nursery garden,slope farm land,deforested-land and abandoned land in the central hilly area of Hunan province.The results show that the soil organic carbon content decreased gradually with the increase of soil depth on 6 kinds of land use types and according to the variation coefficient,it went down as follows: abandoned land(80.09%)economic(forest-land(67.21%)slope farm land(62.41%)forest plantation(58.03%)nursery garden(35.58%)deforested-land(25.32%);that the weighted means of this content were ranked as: deforested-land(9.87)economic forest-land(9.78)abandoned land((7.35))slope farm land(0.62)forest plantation(0.58)nursery garden(0.36);and that there existed a highly significant difference among these 6 kinds of land use types(F=5.43,p0.01) in soil organic carbon content.The results also show that the spatial vertical distribution of soil all-nitrogen content was similar to that of organic carbon and according to the variation coefficient,it was ranked as: abandoned land(55.71%) slope farm land(48.43%)economic forest-land(46.22%)forest plantation((33.75%))deforested-land(20.56%)nursery garden(19.65%);that the weighted means of these contents(g/kg) were as follows: deforested-land(0.84)abandoned land(0.80)slope farm land (0.78)economic forest-land(0.75)nursery garden(0.71)forest plantation(0.62);and that there also existed a highly significant difference among the 6 kinds of land use types((F=4.63),p0.01) in soil all-nitrogen content.The results further show that the spatial vertical distribution of soil ammonium nitrogen and nitration nitrogen had no obvious variation rule but the distribution of hydrolyzed nitrogen had a higher content in top layer than in other layers;that there likewise existed a difference,highly significant among the 6 kinds of land use types(F=2.30,p0.05) in soil ammonium nitrogen content,significant in soil nitration nitrogen content(F=3.34,p0.01) and not significant in soil hydrolyzed nitrogen content(F=1.21,p0.05); and that there was a highly significant positive correlation(R~2≥0.84,p(0.01)) between the organic carbon and the all-nitrogen contents of the 6 kinds of land use types.