Evaluation of the Phosphorus Source Component in the Phosphorus Index for Pastures
- P. B. DeLaune *a,
- P. A. Moorec,
- D. K. Carmand,
- A. N. Sharpleye,
- B. E. Haggardc and
- T. C. Danielb
- a Department of Biological and Agricultural Engineering, University of Arkansas, Fayetteville, AR 72701
c USDA-ARS, Poultry Production and Product Safety Research Unit, Fayetteville, AR 72701
d USDA-NRCS, National Water Management Center, Little Rock, AR 72203
e USDA-ARS, Pasture Systems and Watershed Management Research Unit, University Park, PA 16802
b Department of Crop, Soil, and Environmental Sciences, University of Arkansas, Fayetteville, AR 72701
A phosphorus (P) index for pastures was developed to write nutrient management plans that determine how much P can be applied to a given field. The objectives of this study were to (i) evaluate and compare the P index for pastures, particularly the P source component, and an environmental threshold soil test P level by conducting rainfall simulations on contrasting soils under various management scenarios; and (ii) evaluate the P index for pastures on field-scale watersheds. Poultry litter was applied to 12 small plots on each of six farms based on either an environmental threshold soil test P level or on the P index for pastures, and P runoff was evaluated using rainfall simulators. The P index was also evaluated from two small (0.405 ha) watersheds that had been fertilized annually with poultry litter since 1995. Results from the small plot study showed that soil test P alone was a poor predictor of P concentrations in runoff water following poultry litter applications. The relationship between P in runoff and the amount of soluble P applied was highly significant. Furthermore, P concentrations in runoff from plots with and without litter applications were significantly correlated to P index values. Studies on pastures receiving natural rainfall and annual poultry litter applications indicated that the P index for pastures predicted P loss accurately without calibration (y = 1.16x − 0.23, r 2 = 0.83). These data indicate that the P index for pastures can accurately assess the risk of P loss from fields receiving poultry litter applications in Arkansas and provide a more realistic risk assessment than threshold soil test P levels.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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