Phosphorus mineralization affected by urea in an intensively managed agricultural soil

A mineralizable P fractionin soils has not been considered in the current agronomic soil P test. Organic P might be a potential source of bioavailable P under the influence of specific soil conditions such as N input. In this laboratory incubation study, the effects of urea (0.1-0.3 g N kg(-1) soil) on P mineralization was investigated in an intensively managed agricultural soil using chemical extractions, phosphatase activity analysis, and solution P-31 nuclear magnetic resonance spectroscopy (NMR). All urea application rates stimulated P release and P mineralization after 5 d, and bioavailable P increased for up to 40 d. The result of NMR analysis and phosphatase activity supported a shift from organic P to orthophosphate. Urea applications generally increased labile P from similar to 5 to similar to 24 mu g g(-1). However, acidity generated from the oxidation of NH4+ under the highest urea treatment (0.3 g of N kg(-1) soil) suppressed P mineralization, indicating the degree of urea application rate is sensitive to P mineralization. The results suggested the use of urea could enhance P bioavailability in P-rich agricultural soils. Tapping into reusable organic P resources in soils might be one of the practical and conservative approaches in the current agriculture.