Saturday, 15 July 2006

Phosphorus Storage Capacity of Soils under Various Animal Operations.

Vimala D. Nair, Willie Harris, P. K. R Nair, and Donald Graetz. Univ of Florida, Soil & Water Science Dept, Gainesville, FL 32611

The capacity of a manure-impacted soil to retain Phosphorus (P) relates to risk of P loss from sandy soils to adjacent water bodies. A new concept to calculate the safe P storage capacity per unit volume of soil, based on the P saturation ratio (available P/Fe+Al), is used to predict the “safe lifespan” of a P-impacted soil under different intensities of dairy, beef and poultry operations (Nair and Harris, 2004). The capacity reflects the relative P-conserving effects of alternative management practices. For example, the remaining P storage capacity was greater under silvopasture — the integration of trees, pasture and animals — than under an adjacent treeless pasture under similar management practices as evidenced by the soil P storage capacity of soil profiles. Capacity can also be used as an indicator of areas where animal operations would pose the least threat to the environment. It can also serve as a means of predicting P loss at environmentally problematic levels from soils that have become sources (“negative” storage capacities) due to heavy manure loading. Reference: Nair, V.D., and W.G. Harris. 2004. A capacity factor as an alternative to soil test phosphorus in phosphorus risk assessment. New Zealand J. Agric. Res. 47:491-497.

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