Forms, transformations and availability of phosphorus after 32 years of manure and mineral fertilization in a Mollisol under continuous maize cropping

ABSTRACT

A 32-year field experiment was performed to examine the impact of applications of pig manure and mineral fertilizers alone or in combination on phosphorus (P) forms, transformations and availability in a Mollisol. The concentrations of total P, Olsen P, inorganic P (Pi) and organic P (Po) and their fractions were generally higher in treatments with than without mineral fertilizers and manure, and with high than with low manure rate. The proportions of Olsen P to total P, dicalcium bound P (Ca₂-P) and octacalcium bound P (Ca₈-P) to Pi and labile Po (LPo) to Po were significantly higher in manured than in unmanured treatments. The direct path coefficient of Ca₂-P on Olsen P (1.63) was larger than that of other P fractions on Olsen P (–0.87 to 0.24), and the indirect path coefficients of all P fractions on Olsen P via Ca₂-P (1.50 to 1.62) were greater than those through other P fractions (–0.86 to 0.24). The results suggested that manure promotes accumulation of Ca₂-P and LPo, and mineral fertilizers combined with high-rate manure are especially effective for improving P availability. Contributions of other P fractions on Olsen P are mainly via their indirect effects for Ca₂-P.

Abbreviations: CK: control; NPK: nitrogen, phosphorus and potassium fertilizers; M1: pig manure at low rate; M2: pig manure at high rate; TP: total phosphorus; Pi: inorganic phosphorus; Po: organic phosphorus; Ca₂-P: dicalcium bound phosphorus; Ca₈-P: octacalcium bound phosphorus; Ca₁₀-P: phosphorite bound phosphorus; Al-P: aluminum bound phosphorus; Fe-P: iron bound phosphorus; O-P: occluded iron/aluminum bound phosphorus; LPo: labile organic phosphorus; MLPo: moderately labile organic phosphorus; MRPo: moderately resistant organic phosphorus; HRPo: highly resistant organic phosphorus; PAC: phosphorus activation coefficient; SOC: soil organic carbon; TN: total nitrogen; PCA: principal component analysis.

KEYWORDS:

• Phosphorus fractions
• mineral fertilizer
• pig manure
• chemical sequential fractionation

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by the National Key Research and Development Program of China (Grant numbers 2017YFD0200205 and 2016YFE0112700), the National Natural Science Foundation of China (Grant number 41471196) and the Key Laboratory of Plant Nutrition and Agro-Environment of China (No. KLPN201801-01).