NUTRIENT LEACHING FROM ALFALFA IRRIGATED WITH MUNICIPAL WASTE-WATER

A land-application system's performance in limiting the leaching of ni trogen (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 thr ough 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 t he P applied. Leachate quantities based on the consumptive water use o f the alfalfa as determined by the modified Blaney-Criddle formula wer e unsatisfactory. Instead, leachate quantities were estimated with a s imple model based on the amount of the soil water collected by porous- cup suction samplers. It was recommended that N leaching may be furthe r 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 b relatively harsh climates.