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Temporal changes in the concentrations of plant-available phosphorus (P) in soil (Olsen-P), total soil-P and P activation coefficient (the ratio of Olsen-P to residual-P (i.e. an approximation to total-P)) were measured in plots that received consistent inorganic nitrogen, phosphorus and potassium plus organic fertilizers annually. Maize and winter wheat crops were grown in rotation for 24 years. Olsen-P and P activation coefficient declined significantly in the earlier years (< 12 years) for treatments that did not include any P fertilizer, and increased over the same period for the P-fertilized treatments. The rates of change in the Olsen-P and P activation coefficient values were positively related to P balance. In the later years, the Olsen-P and P activation coefficient plateau values were positively related to the P balance. [ABSTRACT FROM AUTHOR]

Improving N use efficiency (NUE) and reducing the negative impact of N fertilization on the environment are essential for sustaining agricultural production in many intensive farming regions around the world. The objective of this research was to investigate the effect of various fertilization regimes on yield, N uptake, and NUE by maize (Zea mays L.) in long-term (15-yr) experiments performed at four sites (Changping, Zhengzhou, Yangling, and Qiyang) in China. Eight treatments were examined: unfertilized control (CK); inorganic fertilizer (manufactured source) N, N and P, N and K, and N, P, and K; inorganic N, P, and K with manure (NPKM); 1.5′ the rate of NPKM (1.5NPKM); and N, P, and K with maize stover returned (NPKS). Compared with inorganic fertilization, mixed inorganic and manure fertilization (NPKM and 1.5NPKM) resulted in more stable and significantly higher yield and NUE as well as increases in soil nutrient storage at all sites, with the most significant improvement in the acid soil (pH = 5.7) at Qiyang. Phosphorous was identified as one of the most important limiting factors in maize NUE because the NUE at all four sites increased from about 20 to 45% by increasing the available P in the soil. Higher NUEs (up to 70%) were observed mostly from the continuous manure applications. We conclude that manure and P applications are the most important and effective nutrient management strategies for both the acid and alkaline soils in this study for maize production in China. [ABSTRACT FROM AUTHOR]

Microbial biomass phosphorus (MBP) and its relationships with other biological and chemical properties were studied on loess soil with an 11-year long-term fertilization experiment. The results indicated that inorganic fertilizers (F) improved soil microbial biomass carbon (MBC), nitrogen (MBN), and MBP levels and F plus maize stalk (SNPK) improved MBC and MBN. Manuring markedly increased soil MBC, MBN, and MBP levels. Fertilization decreased the ratios of MBC/MBN, MBC/MBP, and MBN/MBP. Microbial biomass phosphorus was positively and linearly correlated with MBC, MBN, organic carbon (SOC), total phosphorus (TP), water-soluble P, and Olsen P but negatively correlated with soil pH. Microbial biomass phosphorus constituted 2% of TP on control (CK) and inorganic fertilizer treatments and 12% on manure plots. Microbial biomass phosphorus to Olsen P ratios were 50% on CK, F, and SNPK and 80% on manure treatments. Measurements of MBP in soil containing high Olsen P were subject to analytical problems of unknown reasons. [ABSTRACT FROM AUTHOR]