Objectives To examine the phosphorus (P) balance and the change of phosphorous availability under long-term fertilization measurements will provide support for the academic management of P.
Methods The used long-term experiment was initiated in 1979 in Harbin, Heilongjiang Province. It consisted of ten treatments, including no fertilizer (CK), four chemical fertilizer treatments (N, P, NP and NPK), solely horse manure (M), and chemical fertilizer plus manure (MN, MP, MNP and MNPK). All treatments had three replicates. Soil total phosphorus (TP) and Olsen phosphorus (Olsen-P) were analyzed, the linear regressions between Olsen-P and P balance was calculated.
Results The contents of soil total P and Olsen-P were improved significantly under P fertilizer applications (P, NP, NPK, MP, MNP and MNPK), but decreased over time under treatments without P applications ( CK, N, M and MN). Phosphorous availability coefficient (PAC) showed yearly declining trend in no P fertilizer treatments but increasing trend in P-containing treatments. The PAC in chemical fertilizer plus manure treatments was higher than that in the chemical P fertilizer alone. With an average annual surplus of P 100 kg/hm2, the soil Olsen-P content was increased by 1.56, 1.45, 1.69, 0.63, 0.53 and 0.96 mg/kg in the P, NP, NPK, MP, MNP and MNPK treatments, while those in the M and MN treatments decreased by 1.38 and 1.24 mg/kg. When the soil P balance was in deficient, the Olsen-P content in the CK and N treatments would be decreased by 1.83 and 1.46 mg/kg for every deficiency of P 100 kg/hm2.
Conclusions Phosphorus fertilizer application, especially chemical phosphate with manure application, can improve the soil Olsen-P, total P content and PAC, while application of nitrogen or horse manure alone would lead to soil P deficit, and decrease the availability of P. Chemical P and manure combined fertilization shows more efficiency in improving the phosphorous availability coefficient than chemical fertilizer alone.
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