Safety amount of pig manure application based on potassium balance and nitrate leaching risk on red soil

The effect of 8-year application of pig manure and lime addition on potassium balance was investigated on red soil (Udic Ferralsols) with maize monoculture in subtropical China. The content of soil available potassium, leaching and uptake of potassium were measured under different application rates of organic manure (0, 59 and 237 kg/hm2 for CK, LM and HM treatment, respectively) and with lime addition (application rates of organic manure 237 kg/hm2 by lime addition 1 t/(hm2.a) for HML treatment). The results showed that continuous manure application increased the content of soil available K and K supply capacity. The K leaching did not increase with increasing manure application rate. More than 69% of potassium from manure was taken up by crop and higher utilization efficiency was found in LM which ultimately resulted in depletion of soil potassium pool. On the contrary, high manure application (HM and HML) annually replenished 48-57 kg/hm2 with lower utilization efficiency. The manure application rate was 180 kg/hm2 when considering only crop K demand and soil K pool balance. Considering the nitrate contamination risk, the manure application should be controlled under 155?kg/hm2 with a supplement of 25 kg/hm2 by chemical fertilizer.