Accumulation of Soil Available Phosphorus under Pig Manure Application Limits Microbial Community Function in Upland Soils

In this study, a two-year pot experiment with a peanut (Arachis hypogaea L.) and radish (Raphanus sativus L.) rotation system was conducted to investigate changes in soil chemical properties and microbial characteristics and to determine the internal relationship of these variables after pig manure application.The selected soil types include Agri-Udic Ferrosols, Ali-Udic Argosols and Ali-Udic Cambisols, which are widely distributed throughout subtropical China.The annual pig manure application amounts were 25, 50, 100, 200, 400 and 800 kg P ha -1 .The results of our experiments showed that the soil pH (R 2 =0.57-0.87,P<0.01), organic carbon (R 2 =0.73-0.91,P<0.01), total nitrogen (R 2 =0.51-0.74,P<0.01), total phosphorus (R 2 =0.81-0.94,P<0.01), available nitrogen (R 2 =0.71-0.92,P<0.01) and available phosphorus (R 2 =0.89-0.97,P<0.01) were positively and linearly correlated with the microbial biomass carbon/nitrogen in the three soils.The relationship between the functional diversity of the microbial community and the available phosphorus was parabolic.According to the most pronounced changes (i.e., the highest values), we deduced that the rational application rate of pig manure should be 100-200 kg P ha -1 in the three soils, which was verified by a lack of significant increase in peanut pod yield when the deduced fertilizer level was exceeded.In brief, our results indicated that excessive accumulation of soil available phosphorus under pig manure application reduced microbial community function, implying that the excessive application of pig manure could reduce soil quality.