Phosphorus Fertility Charateristics Of Black Soil Under Different Land Uses

A 21-year field trial was used to study the effects of ecological factors and fertilization onphosphorus characteristics of fertile black soil under three types of land use: (1) bare land (BL), (2)grassland (GL) and (3) cultivated land with a rotation of wheat-soybean-corn. The cultivated landreceived N and P fertilizers during 1985-1993 and received no fertilizers (CK), N and P fertilizers(NP) or N and P fertilizers along with pig manure (NPM) during 1994-2005. Soil phosphorusdynamics under different types of land use and fertilization management was discussed bydetermining the properties of tested soil and procssing the data of crop yield and amount offertilization. The methods of Jiang and Gu were adopted to evaluate the fractionation of soilinorganic phosphorus. In order to discuss the supply capacity of soil phosphorus, the adsorption ofinorganic phosphorus was evaluated by the methods of Haseman and the release of soil phosphruswas determined by the methods of Cooke.Besides, a pot culture trial was conducted in 2006 tostudy the soil P supply capacity and use efficiency of P fertilizers.While there was no P input or removal in the BE and NE, the CK had a net P loss of 174kgha^-1, whereas the NP had a net gain of 96 kg ha^-1 and the NPM 504 kg ha^-1. Increasing net P inputincreased both Olsen P and total P in the 0-20cm soil. The amounts of NaHCO₃-extractable (Ca₂-P) and NH₄Ac-extractable P fractions (Ca₈-P) were in an order of NPM＞NP＞CK＞GL＞BL. TheH₂SO₄-extractable fraction (Ca₁₀-P) was lowest in the BL and highest in the NPM but was similarin the other treatments. The CK had the least, and the NPM had the highest amounts ofNH₄F-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-Pdecreased with increasing P input into the system. Soil P adsorption was in an order of CK＞GL＞NP＞BL＞NPM, whereas P release was in an order of NPM＞＞NP＞CK＞GL＞BL. Soil P supplycapacity was in the order of NPM＞NP＞GL＞CK＞BL. Use efficiency of P fertilizers was in theorder of CK＞GL＞BL＞NP＞NPM.It was concluded that grassland could maintain soil P while annual applications of chemicalfertilizers and animal manure increased both labile and non-labile P pools in the cultivated land.The use of the pig manure clearly decreased P adsorption and increased P release. The current ratesof chemical and organic P used in this study obviously exceed the crop demands, and should be atleast halved in the NPM system. Although the vertical movement of P is minimal in this soil type,the available P (Olsen-P) decreased over time in the bare land and grassland. It is unknown whetherthe decreased available P is a result of P loss through surface runoff during wet seasons. Furtherstudies with this respect are required.