Study On Spatial Variability And Influencing Factors For Soil Phosphorus In Yibin

Being closely linked with the phisilogical processes such as organic synthesis and cell division, phosphorus is one of the three elements necessary for the growth of plants. The content of phosphorus in soil of our country is on the whole low with obviously different spatial and temporal distribution. Scientific application of phosphatic fertilizer and rational allocation of soil phosphorus have become the major question to be solved for developing our modern agriculture. With the situation in Yibin City in Sichuan Province as an example, in the thesis, spatial variability characteristics of soil phosphorus are studied at two different dimensions by geostatistics, RBF neural network, GIS and other technologies; in addition, in the thesis, the influences of structural factors such aparent soil material and organic matter on the spatial variability of the soil phosphorus are analyzed and measures for managing the soil phosphorus at the researched areas are discussed. The major research results are as follows:(1) Variation of the soil phosphorus of different forms at different dimensions differs. With descriptive statistics of the large dimension and the small dimension compared, it is found that the variation at the small dimension is mostly smaller than that at the large dimesion (excluding Fe-P, O-P). as far as the single dimension is concerned, the variation of the following substances in the large dimension:organophosphorus< total phosphorus< O-P< Fe-P< Al-P< rapid available phosphorus< Fe-P.(2) Distribution characteristics of soil phosphorus at the small dimension are clearer. It is demonstrated by analyzing varatiaon characterisctics that the ratio of nugget value to sill value at the large dimension is higher than that at the small dimension, showing clear dimension characteristics. In addition, the space distribution of the phosphorus also shows that different influencing factors within the area are closely linked with the distribution characteristics of the soil phosphorus, with the research dimension decresed, the influences of the structural factors become more obvious and forecast accuracy of the content of the phosphorus incearses accordingly.(3) In 2009, on the whole, soil phosphorus increased compared with that in 1982 but remain in a relatively low level. In 2009, total phosphorus and rapid available phosphorus in soil of the researched area saw remarkable improvement compared-with overall soil examination data in 1982 in terms of content ranked distribution, yet the overall content remains at a low level. Therefore, phosphorus management needs to be further strengthened and phosphorus resources should be allocated rationally.(4) Influences of of different influencing factors on spatial variability of soil phosphorus differ. The total phosphorus contents of Quaternary system sediments are excessively high, however, the contents of the rapid available phosphorus in the sediments remain at the intermediate and low level; when pH value is below 6.5, the content of the rapid available phosphorus in soil is higher while that of the total phosphorus in soil is lower; the organic matters are obviously related to content of the total phosphorus but not to the rapid available phosphorus; the content of the phosphorus in arable land is higher than that of wild grass land; the content of the total phosphorus in yellow limestone soil is higher while the content of the rapid available phosphorus in the yellow limestone soil is lower; the smaller the grain size is, the higher the phosphorus content level is; when it is below 500m above sea level, the content of phosphorus, the rapid available phosphorus in particular stays at high level.(5) Local conditions should be taken into account when formulating measures for managing soil phosphorus. The space distribution of the soil phosphorus in different areas differs significantly. It is suggested that general measures and zone management measures are integrated by taking into account the spatial distribution of the phosphorus in different areas so as to provide references for studing scientific management of the soil phosphorus and rational application of fertilizer in the reeaserched area.