Phosphorus leaching at cold temperatures as affected by wastewater application and soil phosphorus levels

Land application of waste-water in the northern-tier United States during winter months has been suggested as a means to reduce cost of building storage lagoons. A study was initiated in 1996 to assess land application of potato-processing wastewater on a 120-ha field at Park Rapids, MN. One objective of this study was to evaluate the effects of soil P levels and temperature on P leaching in soil columns. In this paper, we report the P sorption, desorption, and leaching characteristics of a high-P (>200 mg kg^-1) and a low-P (<25 mg kg^-1) surface soil from the wastewater irrigation site. The leaching experiment was done with wastewater at 4 ± 2 or 10 ± 2°C. The high-P soil resulted in an equilibrium P concentration of 8.0 mg L^-1 compared with 0.14 mg L^-1 for the low-P soil. When low-P wastewater was applied to the high-P soil, the soil acted as a P source, and the total phosphorus (TP) concentration in the leachate was 3.5 times higher than the input TP concentration (C₀). When high-P wastewater was applied to the high-P soil, the soil acted as a P sink retarding the TP concentration in the leachate by 80%. Phosphorus desorption was higher at 10°C compared with 4°C. The results showed that depending on P levels of the soil and the wastewater, reduction or increase in leachate P will occur below the surface soil. However, further mobility of this P under field conditions will depend on the volume and rate of percolating water as well as the sorption-desorption characteristics of the subsoil.