Nutrient Leaching from Alfalfa Irrigated with Municipal Wastewater

Abstract

A land‐application system's performance in limiting the leaching of nitrogen (N) and phosphorus (P) through the soil zone was evaluated. The system was located in Heber Valley, Utah, which has an average frost‐free growing season of only 100 days. The amount of N that leached through the soil zone was 6.3 kg N/ha or 24% of the N applied. The amount of P that leached through the soil zone was 0.84 kg P/ha or 0.2% of the P applied. Leachate quantities based on the consumptive water use of the alfalfa as determined by the modified Blaney‐Criddle formula were unsatisfactory. Instead, leachate quantities were estimated with a simple model based on the amount of the soil water collected by porous‐cup suction samplers. It was recommended that N leaching may be further reduced by growing a winter‐hardy grass, such as smooth bromegrass, with the alfalfa and by reducing leaching during the growing season by limiting irrigation to periods when soil‐water supplies are low. This study demonstrates that land‐application systems can be an effective method of wastewater management for mountain communities influenced by relatively harsh climates.