The Response Of Soil Phosphorus Composition Hill Area In Loess Plateau To Vegetation Restoration

The intact vegetation resources in loess plateau was greatly damaged, which was accompanied with frangibility of ecological system, aggravation of land degradation and serious soil corrosion.After more than 20 years of vegetation afforestation, the area of land that was covered with plant and grass was increased, the ecological environment was gradually improved. Soil phosphorus composition in different vegetation type, restoration stage and on typical slope landform on local hill area in loess plateau was investigated. The phosphorus effect in these vegetation type, restoration stage and slope landform was also evaluated.(1)Phosphorus in soilTotal phosphorus and water-soluble phosphorus in soil was generally stayed in low level. Inorganic phosphorus took a large portion in total phosphorus composition, Ca-P was the main form of inorganic phosphorus, O-P was remained below the value that could be deteced. The content as well as proportion of inorganic phosphorus was changed according to the order as follows : Ca10-P>Ca8-P>Fe-P>Al-P>Ca2-P. Organic phosphorus took a small portion in total phosphorus composition, medium active organic phosphorus was the main form of organic phosphorus. The content as well as proportion of organic phosphorus was changed according to the order as follows : medium active organic phosphorus>medium stable organic phosphorus>high stable organic phosphorus>active organic phosphorus.(2)The effect of restored vegetation on soil phosphorusPhosphorus content in soil covered with artificial vegetation was obviously lower than that in cultivated soil, soil total phosphorus was decreased after long-term of vegetation afforestation. In soil covered with deep-root vegetation such as Caragana intermedia and Populus simonii, Ca2-P,Ca8-P,Al-P,the content of active organic phosphorus and medium active organic phosphorus was mainly stayed in high level, the content of active phosphorus was stayed in comparatively high level. In soil covered with shallow-root vegetation such as Artemisia gmelinii was stayed in comparatively low level.(3)The effect of time span in vegetation restoration on soil phosphorusAs number of years in vegetation restoration extended, the content of soil total phosphorus as well as organic phosphorus was greatly decreased, while the content of inorganic phosphorus was observed increased, the content and proportion of inorganic phosphorus kept almost the same. While that of organic phosphorus showed increased trend. High stable organic phosphorus was comparatively stable as time extended, the content and proportion of the rest inorganic and organic phosphorus was slightly decreased at the prophase of vegetation growth and was reached to climax value at metaphase of vegetation growth and was decreased again at anaphase of vegetation growth.(4)The distribution of soil phosphorus along the slopeSoil total phosphorus, inorganic phosphorus and water-soluble phosphorus was increased in linear function from slope top to slope toe, the medium active organic phosphorus and active organic phosphorus was in high activity,it moved to downwards of slope and accumulate there, there was not much change observed in medium stable organic phosphorus and high stable organic phosphorus along the slope.