Impact of compost, manure, and inorganic fertilizer on nitrate leaching and yield in a six-year maize-alfalfa rotation.

An accurate estimate of nitrate (NO3–N) leaching from agricultural land is critical to environment impact studies. Although NO3–N are almost always present in groundwater, their continued increase in managed agricultural land can lead to nitrate concentrations in groundwater above acceptable human health standards. The amount of NO3–N leached during the growing season may be minimal compared to leaching losses that occur between the harvest of one crop and the planting of the next. In this study we compared the effect of inorganic N and raw and composted animal manure on crop productivity and N leaching under field conditions in a maize–alfalfa system using undisturbed drainage lysimeters in Michigan. The cropping system rotation consisted of 3 years of continuous maize (Zea mays L.) and 3 years of continuous alfalfa (Medicago sativa L.). One cropping system consisted of a maize crop grown in the 1994–1996 seasons and alfalfa in the 1997–1999 seasons. The other cropping system was alfalfa (1994–1996) then maize (1997–1999). Four N treatments were imposed on the cropping systems. Treatment 1 was a check, no N fertilizer; Treatment 2 was manure; Treatment 3 was compost; Treatment 4 was inorganic fertilizer. No significant differences in yields of maize and alfalfa were found between N treatments in the 6-year rotation, although the no N treatment in maize had consistently lower yields. The highest amount of NO3–N leaching was measured in the manure treatment with a mean annual value of 55 kg NO3–N ha1 in maize–alfalfa rotation and 59 kg NO3–N ha1 in alfalfa– maize, followed by compost (35 kg NO3–N ha1 in alfalfa–maize and 30 kg NO3–N ha1 in maize–alfalfa), inorganic N (33 kg NO3–N ha1 in alfalfa–maize and 25 kg NO3–N ha1 in maize–alfalfa) and no N (27 kg NO3–N ha1 in alfalfa–maize and 25 kg NO3–N ha1 in maize–alfalfa). The highest rates of NO3–N losses were also observed in the manure treatment with a mean value for the 6-year rotation of 0.14 kg NO3–N mm1 in alfalfa–maize and 0.35 kg NO3–N mm1 in maize–alfalfa.