PHOSPHORUS AVAILABILITY CHANGES WITH POULTRY COMPOST AGE

Authors: Adler, Paul; Sikora, Lawrence

Submitted to: Communications in Soil Science and Plant Analysis
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/1/2002
Publication Date: 3/1/2003
Citation: ADLER, P.R., SIKORA, L.J. PHOSPHORUS AVAILABILITY CHANGES WITH POULTRY COMPOST AGE. COMMUNICATIONS IN SOIL SCIENCE AND PLANT ANALYSIS. 2003.

Interpretive Summary: As compost matures, it reduces the amount of nitrogen in manure that can be leached into the ground water. However its' effect on the amount of phosphorus that can be lost to surface runoff is not clear. The composition of organic matter changes as compost matures and that change can affect the capacity of the soil to retain phosphorus. The goal of this study was to determine if compost maturity affected the amount of phosphorus retained b soils amended with compost. Turkey litter was composted and applied to soil, and plant available phosphorus and that susceptible to runoff losses were measured over time. Plant available phosphorus was not affected by compost maturity. However, more phosphorus was available for runoff losses from biologically active, immature compost. That was reflected in soil measurements when the capacity of the soil to retain phosphorus was not sufficient to offset the effects of the compost addition. Because water extractable P is seen in runoff events and is directly related to water quality decline, caution should be exercised in applying immature composts to areas within the watershed which are most vulnerable to P loss in surface runoff and erosion.

Technical Abstract: Composting reduces the available N content of organic materials by immobilizing it and converting it to a slow release form. The effect of composting on P is less clear. Adding compost to soil can increase water extractable soil P by direct addition, dissolution, displacing sorbed, or reducing sorption capacity for P. Organic acids can affect soil P and vary with compost maturity. The objective of this study was to examine the effect of compost maturity on soil P. Turkey litter was mixed with orchard grass at a 3:1 volume ratio, turned frequently, and temperature, carbon dioxide, and oxygen measured regularly. Compost samples were taken at day 0 when the compost was made, and at weeks 2, 4, and 8. Compost samples were added to a loam and clay soil and then incubated for 8 weeks. At 1d, and 2, 4, and 8 weeks, water and Mehlich 1 extractable P were determined. Age of compost did not affect the Mehlich 1 extractable P fraction but did affect water extractable P on day 1 in the loam soil. These data suggest that water extractable P may increase when loam soils are amended with biologically active, immature compost or when the sorption capacity of the soil is not sufficient to offset the effects of the compost addition. Because water extractable P is implicated in runoff events, caution should be exercised in applying immature composts to critical source areas within the watershed which are most vulnerable to P loss in surface runoff and erosion.