Correlations between Phosphorus Fractions and Total Leachate Phosphorus from Cattle Manure– and Swine Manure–Amended Soil

Abstract

Although many studies have examined the effect of different application rates of cattle manure, swine manure, and urea fertilizer on the distribution of phosphorus (P) fractions in soil, few studies have correlated P fractions in soil with inorganic P (Pi) and organic P (Po) in leachates. As part of a long-term field study, cattle and swine manures were applied to a loamy soil based on a nitrogen (N) content equivalent of 100 (low) and 400 (high) kg total N ha−1 yr−1 and were compared to urea fertilizer at 100 kg N ha−1 yr−1 and an unamended control soil. Readily available Pi [resin and sodium bicarbonate (NaHCO3)] was significantly greater in cattle manure– and swine manure–amended soil at a high application rate than in the control. With some exceptions, urea did not significantly affect P fractions in sequentially extracted P pools. Leaching of Pi and Po was at levels of environmental concern when cattle and swine manures were applied at the high application rate but not at the low application rate. Cattle manure had significantly greater concentrations of Pi and Po removed by leaching compared to swine manure, most likely because of its narrow N/P ratio and greater amount of P added. Positive correlations were observed between resin Pi and total leachate Pi and between NaHCO3-Pi and total leachate Pi, indicating the value of these measurements in predicting P mobility. The results suggest that a threshold (40 μg P g−1 of soil) must be exceeded before a positive correlation occurs.