SOIL PHOSPHORUS DYNAMICS IN RESPONSE TO DAIRY MANURE AND INORGANIC FERTILIZER APPLICATIONS

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Abstract

In modern agriculture practices, the application of plant nutrients to soil is usually required for sustained high crop yields. Manure is generally applied to meet crop N needs. The impact of N-based manure application rates on soil P transformations should therefore be evaluated for efficient utilization of both manure N and P. In this study, 11 dairy manure and inorganic fertilizers were added to two Maine soils to supply 100 mg organic N kg−1 soil. Our data showed that the general distribution patterns in manure-amended soils for three P species, inorganic P (Pi), enzymatically hydrolyzable organic P (Peo), and nonhydrolyzable organic P, basically followed the trend of changes for inorganic fertilizer amended (control) soils, indicating that soil properties played a major role in controlling P dynamics. In H2O and NaHCO3 fractions, soil bioavailable P (Pi and Peo) was linearly related to added P. However, NaOH-extractable soil P was not closely related to the P applied in the manure. This work confirmed that a single application of manure impacted soil bioavailable P in a manner similar to fertilizer and did not significantly impact soil P properties and environment. This means that growers converting from conventional to organic practices (i.e., where manure is the sole source of N and P) may estimate manure bioavailable P to meet their short-term P needs. Further studies need to be conducted to determine if similar results can be found under field conditions.

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