Response characteristics of Olsen-P to P balance in yellow paddy fields of southern China

ObjectivesIn order to provide theory for phosphate (P) fertilizer application in the yellow paddy, a study was conducted to research the relationship between P accumulation and its efficiency.

MethodsThe variation and accumulate of P in paddy fields were studied in a 33 years’ long-term experiment. Four fertilizer treatments were setup: no fertilizer (CK), chemical fertilizer (NPK), chemical fertilizer plus cattle manure (NPKM), and chemical fertilizer plus straw (NPKS) and available P–P response coefficient was calculated.

ResultsThe contents of soil available and total P in the CK treatment decreased with the treatment years in both the double-rice and the single-rice systems, and those in the other three treatments increased with the fertilizer treatment years under double-rice system (1983–2004) and decreased in single rice system (2005–2015). Until 2015, the contents of soil available P in the NPK and NPKS treatments were 9.7 mg/kg and 8.7 mg/kg, which were significantly lower than that of initial soil sample in 1983, and decreased by 8.3 mg/kg and 9.3 mg/kg, respectively. The available P content in the NPKM treatment was 18.0 mg/kg in 2005, which was in line with initial soil sample. The phosphorous activity coefficients of the CK, NPK, NPKM and NPKS treatments were 2.9%, 3.5%, 4.7% and 4.1% in turn, those in the NPKM and NPKS treatments were significantly higher than that in the NPK treatment. There was a linear relationship between the balance of P and soil available P contents in all the treatments except that in NPKS under double-rice system. Under double-rice system, annual soil P surplus of 100 kg/hm² would lead to the increment of soil available P contents of 4.5 and 11.2 mg/kg in the NPK and NPKM treatments, and under single-rice system, annual soil P defect of 100 kg/hm² would lead to the decrement of available P content by 14.6, 23.9 and 25.9 mg/kg in the NPK, NPKM and NKPS treatments, respectively. The soil could keep in balance when the amount of P fertilizers was 26.2 kg/hm².

ConclusionsAvailable P content is closely related to the balance of soil P. The available P response coefficient of the NPK combined with manure or straw fertilization is higher than that of NPK fertilization under the equivalent phosphorus balance. Acceleration response of available P is higher under phosphorus-deficient conditions than phosphorus-sufficient conditions.