Changes of Organic Matter, N, P and K Content of Soils in Red Soil Areas Under Long-Term Experiment

The content of organic matter (OM), nitrogen (N), phosphorus (P), and potassium (K) in the three selected soils, includingCalcaric Purpli-Orthic Primosols (purple sand-shale parent material), Dystric Turbi-Anthric Primosols (quaternary red clayparent material) and Typic Udi-Sandic Primosols (granite parent material) were studied under a long-term experiment byusing crop straw and inorganic fertilizers at the Hunan Red Soil Experiment Station of Chinese Academy of AgriculturalSciences. The results showed that the contents of OM, N, P and K in the three selected soils increased after 23 yearsapplication of crop straw and inorganic fertilizers, but the contents increased much less when crop straw or inorganicfertilizers was applied alone. The nutrient contents in the three soils developed from granite changed more remarkablythan those in the soil derived from quaternary red clay and purple sand-shale. It was also found that the contents of OM,N, and P increased slightly in the treatments without applying fertilizers or returning the crop straw to the root bed.Combined application of inorganic fertilizers and crop straw could remarkably increase the contents of OM, alkali-hydrolyzable N and available K, the positive correlation between application of organic fertilizers and increase of OM insoil did not always happened, it provided evidence for the relation between appropriate C/N ratio and accumulation of OMin soil. The increase of nutrient content was influenced by the soil properties. By comparing the contents of nutrient in0-20 cm depth in the three different soils, it was concluded that the most increases of OM, alkali-hydrolyzable N, andavailable P were observed in Typic Udi-Sandic Primosols with the average increase by 3.03, 27.38, and 21.73 mg kg-1,respectively. The available K increased in Dystric Turbi-Anthric Primosols with the average increase by 25.82 mg kg-1,while it decreased in Calcaric Purpli-Orthic Primosols and Typic Udi-Sandic Primosols. It was concl