LAUSR

ABSTRACT It is crucial to know how management factors influence soil test phosphorus (P) since non-point P sources for surface waters are becoming recognized as a problem throughout the USA. Phosphorus fertilizer and crop residue can impact the cycling of P in soils. An eight-year crop residue removal and P fertilization (0, 7.3, 14.7 and 29.4 kg P/ha) as triple superphosphate (TSP) experiment were conducted to determine the effect of P applications on soil P fractions. Significant differences in Bray-l extractable P were observed after only one year of P applications. Extractable P at the highest P rate was significantly higher than all the other rates. For each 5.6 kg P/ha added or removed, Bray-l P changed by 1 mg/kg. Fertilizer P applications did not significantly change the organic P (Po) levels, microbial P (Pm) or soil pH, whereas residue treatments had effects on them except for soil pH. Residue-retained plots had significantly higher Pm in the last two years of study, and Po in the 8th year, compared with residue-removed plots.