| Nutrient losses from agricultural soils are one of the principal causes of surface water quality impairment. A study was conducted in animal operations (dairy cattle and poultry) of Puerto Rico, to quantify nitrogen (TKN), phosphorus (DP and TP), dissolved organic carbon (COD) and heavy metal (Cu, Fe, Zn) runoff concentrations. Results were used to validate at the field level the Caribbean Phosphorus Index (CPI), a tool developed for the identification of agricultural soils with high risk of P losses to surface waters. Runoff fractionators and a pluviograph were installed in each farm to monitor rainfall duration and intensity. Eighty-five percent of the area in the poultry farm had soil P levels (Olsen) in excess of 35 mg P kg-1. In the dairy farm, only 35% of the total area, exceeded the 35 mg P kg-1 threshold. Average nutrient concentration losses in the poultry farm were 5.87 mg DP L-1, 4.82 mg TP L-1, 0.14 mg Cu L-1, 4.33 mg Fe L-1 and 1.36 mg Zn L-1. Those values were significantly higher than concentration losses at the dairy farm (2.29 mg DP L-2 and 1.79 mg TP L-1, 0.03 mg Cu L-1, 0.69 mg Fe L-1 and 0.70 mg Zn L-1). In both farms runoff P concentration exceeded 1 mg L-1, a value that has been tentatively proposed by USEPA as the maximum desirable concentration in surface runoff from agricultural fields. The CPI ranked plots in the dairy manure in the Medium category for P loss vulnerability, and the poultry farm plots in the High category. |
