Research On Phosphorus Availability And Leaching Effect Of Purple Soil Under Different Fertilizing Measures

Crop residue degradation was of great importance in soil phosphorus cycle. To compare the effects of plant residues with different phosphorus(P) concentration in the process of degradation on phosphorus availability of low P purple soil, and evaluate the effects of plant properties on changes of soil P availability, two kinds of neutral and acid purple soil with adding eight kinds of different P concentration plant residues were analyzed by using lab incubation experiment at 0 d,14 d,28 d,56 d four culture period. Soil drying and rewetting process was a common form of abiotic stress. Based on clearing variation of purple soil P availability under different fertilizing measures, in order to investigate the influence of soil rewetting rate on P leaching and relationship between soil microbial biomass carbon(MBC) and P concentration in leachate, and to assess the influence of rewetting rate on soil P leaching dynamic under different fertilizer treatments, four kinds of neutral purple soils of long-term different fertilizer treatments and cultivated purple soils with adding plant residues were analyzed by using simulating lab test at rewetting rate of 0 h,2 h,4 h,24 h and 48 h. The research looked forword to providing theoretical reference for straw returning technology and theoretical basis for reasonable water and fertilizer field management in Three Gorges. The main results of the thesis were listed below:(1) Adding plant residues to soil significantly increased the soil Olsen-P content, the Olsen-P increased with the increasing of plant P concentration; Adding plant residues had a short-term excitation effect on the soil P, neutral purple soil Olsen-P as well as acid purple soil Olsen-P gradually reduced with the extension of culture period, Olsen-P content was highest at 0 d and was lowest at 56 d.(2) According to the P classification results, there was the conclusion that, along with the extension of culture period, the active P of neutral purple soil gradually turned into inactive P, making P fixed and reducing soil P availability, all kinds of forms of P of neutral purple soil basicly keeped stable until 56 d; the active P of acid purple soil also reduced gradually with the extension of culture period, but the inactive P declined and microbial P increased during the period of 28-56 d, there was a trend that inactive P turned into active P in acid purple soil at the later culture period. It concluded that adding plant residues was more advantageous to enhance the P availability of acid purple than neutral purple soil.(3) The soil cumulative respiration intensity was significantly positively related to N, P content of plant residues, and was significantly negatively related to plant C/N, C/P. Meanwhile, soil Olsen-P also was significantly positively related to C, N and P content of plant residues, and was significantly negatively related to plant C/N. So it was concluded that higher phosphorus concentration of plant residues was more conducive to improve soil P availability, at the same time, the plant residues C, N, C/N and C/P could indirectly effect soil P availability by changing soil microbial activity.(4) The soil rewetting rate was the one of most important factors to affecting phosphorus leaching. The P leaching events of all fertilizer treatments occurred mainly at rapid rewetting rate condition, the concentration of all kinds of forms P was highest at 2 h. At the fast rewetting condition as 0 h,2 h,4 h, the TDP and DOP concentration of dry soil in NPK and MNPK fertilizer treatments was significantly higher than CK and M treatments, but the difference between the groups was not obvious at the slow rewetting condition at 24 h and 48 h. So it was the conclusion that slower rewetting was an important measure to prevent P leaching from soils especially for the soils applied chemical fertilizers, and it was of great significance to water management in the process of agricultural production.(5) The simulating lab test analysis results showed that, the range of DOP/TDP and MRP/TDP respectively was 50.91%-50.91%,7.81%-49.09%in long-term fertilization treatment dry soil leachate, and in fresh soil leachate the range of DOP/TDP and MRP/TDP respectively was 31.77%-31.77%,9.02%-68.22%. It cocld be concluded that the proportion of DOP accounted for TDP was higher than that of MRP accounted for TDP in leachate, DOP was the primary leaching part in leachate, so organic phosphorus was an important source of farmland phosphorus non-point source pollution, and applying organic fertilizer with NPK fertilizer increased the risk of P leaching in paddy fields. Then it was of great importance to pay attention to the application of organic fertilizer in the process of agricultural production.(6) The microbial biomass carbon of all the fertilizer treatments minimized under 2 h rewetting condition, the same as microbial biomass carbon, the microbial biomass phosphrous increased with the decline of rewetting rate. The slower rewetting rate was more beneficial to enhance soil microbial activity, and organic fertilizer NPK treatments(MNPK) had a more obvious enhancement effect to it.(7) With the decreasing of rewetting rate, the microbial biomass carbon content of rewetted dry soil with TP, TDP and DOP concentration in leachate had a very significant negative correlation, but there no linear correlation between microbial biomass carbon and TP, TDP, DOP and MRP concentration in leachate of rewetted moist soils. So it could speculate that the P leached from soil experienced drying-rewetting was mainly derived from soil microbes, and the P leached from moist soils not derived from soil microorganism but possibly from soil colloid and soil solutes.