Effects of 29-year long-term fertilizer management on soil phosphorus in double-crop rice system

Rational soil phosphorus (P) management is significant to crop production and environment protection. Little information is available on soil Olsen-P balance and critical values in double-crop rice in China. The main aim of the study was to relate soil Olsen-P to apparent P balance and to determine Olsen-P critical value for early and late rice using data from a 29-year study (1984~2012) at the Jiangxi province. The results showed that Olsen-P decreased by 0.12~0.26 mg/kg/year without P addition and increased by 0.56~2.52 mg/kg/year with P fertilization. Olsen-P decreased by 0.30 mg/kg for CK and NK under an average deficit of 100 kg P/ha, and increased by an average of 9.10 mg/kg in treatments with organic manures and were 4.55 times higher than chemical fertilizers with 100 kg/ha of P surplus. The critical values for early and late rice were 22.70 and 22.67 mg/kg, respectively. The average Olsen-P content is 90.89 mg/kg after 29-year application of chemical fertilizer and manures. Therefore, decreasing the amount of total P input and increasing the compost portion should be recommended to improve food production and protect environment in red paddy soils in south China.