Soil, groundwater, and alfalfa yield response to manure and compost applications in an arid environment

Abstract

The assessment of environmental degradation from farming practices has received recent attention due to the concern for sustainable agriculture. The United States Department of Agriculture and the Environmental Protection Agency have set forth the Unified National Animal Feeding Operation Strategy to protect the nation's water resources from contamination. The Unified Animal Feeding Operation Strategy requires that field application of manure, a common fertilization method and manure disposal practice, may not exceed crop nutrient needs. This requirement necessitates studies to determine how the multiple variables involved interact so that farmers may comply with the regulation. In this research, the effects of the application of manure, both fresh and composted, on a production alfalfa (Medicago sativa L.) field was examined. Manure and compost were applied to a production alfalfa field to determine the impact on alfalfa yield, soil nutrient content, and the potential for nitrate leaching. A conventional "no nitrogen added" treatment was also maintained as a control. Manure and compost were applied after each harvest in amounts such that the amount of nitrogen removed in the alfalfa harvest was replaced with the same amount of nitrogen in manure or compost. Application rates varied from 35 to 476 kg nitrogen ha⁻¹ after each harvest. It was found that the finer particles of the compost incorporated into the soil profile better than the chunky form of the manure. Soil analysis down to 150 cm depth showed that the compost treatment plots contained nearly 3000 kg total nitrogen ha⁻¹, the manure plots contained about 1750 kg ha⁻¹, and the no nitrogen plots had approximately 1400 kg ha⁻¹. Final PO₄-P soil analysis revealed that compost plots contained about 125 kg PO₄-P ha⁻¹, manure plots had approximately 115 kg ha⁻¹, and no nitrogen plots had only 20 kg ha⁻¹. Alfalfa yield did not vary between treatments throughout the one and a half year study. Also, no detectable nitrate or phosphate was found in the leachate collected from each of the treatments.