Monday, November 5, 2007 - 2:15 PM
121-5

Nutrient in Runoff after Simulated Rainfall from Tropical Soils Amended with Dairy Manure Sludge.

David Sotomayor-Ram�rez1, Gustavo Mart�nez1, and Luis P�rez-Alegr�a2. (1) Agronomy and Soils Department, University of Puerto Rico � Mayag�ez Campus, College of Agricultural Sciences, Mayag�ez, PR, (2) Agricultural and Biosystems Engineering Department, University of Puerto Rico � Mayag�ez Campus, College of Agricultural Sciences, Mayag�ez, PR

Excess nutrients in runoff from soils amended with dairy-manure sludge (DMS) can contribute to water-quality degradation. Most of the dairy farms in Puerto Rico have overhead irrigation systems in which pasture fields receive DMS from retention lagoons following USDA-NRCS code 590 specifications. Nutrient and sediment losses were quantified from DMS amended pasture fields at levels ranging from of 41 to 68 kg N/ha and 14 to 23 kg P/ha in an Oxisol and an Ultisol having �medium� and �high� soil test phosphorus (STP) levels of two dairy farms in Puerto Rico. Concentrations of dissolved phosphorus (DP), total phosphorus (TP) and NO3-N at 30 minutes of runoff after simulated rainfall of 70 mm/hr were repeatedly quantified 1, 7, 14 and 21 days, following DMS application. Unamended soils within the range of soil test levels evaluated, have P concentrations in runoff that are below suggested environmental threshold limits. Soils with �high� STP levels had higher runoff DP and TP concentrations than soils with �medium� STP levels 1-day following DMS ammendment. Phosphorus-sorption saturation phenomena may explain that, at equal levels of DMS amendment runoff DP and TP concentrations decreased with time in soils having �high� STP, yet concentrations were similar at all time periods in soils having �medium� STP. The differences of P concentrations in runoff were greater between amended and unamended soils with �high� STP levels, than in soils with �medium� STP levels. Nitrate concentrations in runoff were greatly influenced by DMS application, STP level and time after application. Runoff P concentrations from these tropical soils are influenced more by the DMS amendment when the soils test �high� than in when soils test �medium� in STP.