Changes in phosphorus fractions, sorption and release in Udic Mollisols under different ecosystems
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A 20-year field trial was conducted to study the effects of ecological factors and fertilization on phosphorus characteristics of fertile Udic Mollisols under three ecosystems: (1) bare land ecosystem with no vegetation or fertilizers (BE), (2) natural ecosystem with native grasses but no fertilizers (NE) and (3) agroecosystem with a rotation of wheat–soybean–corn. The agroecosystem had received N and P fertilizers during 1985–1993 and had received no fertilizers (CK), N and P fertilizers (NP) or N and P fertilizers along with pig manure (NPM) during 1994–2005. While there was no P input or removal in the BE and NE, the CK had a net P loss of 174 kg ha−1, whereas the NP had a net gain of 96 kg/ha and the NPM 504 kg ha−1. Increasing net P input increased both Olsen P and total P in the 0–20-cm soil. The amounts of NaHCO3-extractable (Ca2–P) and NH4Ac-extractable P fractions (Ca8–P) were in an order of NPM > NP > CK > NE > BE. The H2SO4-extractable fraction (Ca10–P) was lowest in the BE and highest in the NPM but was similar in the other treatments. The CK had the least, and the NPM had the highest amounts of NH4F-extractable (Al–P) and NaOH–Na2CO3-extractable fractions (Fe–P). Among the inorganic P, the percentage of Ca2–P, Ca8–P and Al–P increased, whereas that of Fe–P, occluded P and Ca10–P decreased with increasing P input into the system. Soil P adsorption was in an order of CK > NE > NP > BE > NPM, whereas P release was in an order of NPM ≫ NP > CK > NE > BE. The study concluded that soil P can be sustained under the natural ecosystem while annual applications of chemical fertilizers and animal manure increased both labile and non-labile P pools in the agroecosystem.
KeywordsAnimal manure Ecosystems Fractionation Long term Nutrient management P sorption
This research was supported by the Knowledge Innovation Project of Chinese Academy of Sciences (KSCX2-YW-N-002) and the National Basic Research Program of China (2005CB121101). We thank Professor G X Pan for soil taxonomy, and the editor and two anonymous referees for their constructive comments.
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