Eco-efficient choice of cropping system for reducing nitrate-N leaching in an agricultural watershed

Eco-efficiency analysis framework was used to evaluate joint economic and environmentally optimal N application rates for alternative cropping systems managed in a watershed in Atlantic Canada. Eco-efficiency indexes were estimated as the ratio of economic returns from N fertilizer application to groundwater-N leaching associated with crop production. Trade-offs between crop yield and associated reduction in groundwater-N leaching were also estimated. Data for the analysis were generated using the soil and water analysis tool modeling, and allowed for evaluating crop yield and groundwater-N leaching effects for a given crop in rotations assumed to be managed at varying N fertilizer application rates. The cropping systems evaluated included: (i) corn-based cropping systems involving corn–corn–alfalfa–alfalfa–alfalfa (CCAAA, and CCCAA) rotations; (ii) potato-based cropping systems involving potato–corn–barley–potato–corn (PCBPC and PBWPC); and (iii) vegetable-horticulture cropping system involving potato–winter wheat–carrot–corn. Cropping systems were compared under conventional tillage (CT) and no-till (NT) systems. Estimated eco-efficient N fertilizer rates were substantially lower than current provincial nutrient management plan (NMP)-recommended rates, and estimated maximum economic rate of nitrogen fertilizer. However, the actual amounts depended on the crop and rotation system. CCAAA-CT was the eco-efficient choice of rotation system among the corn-based cropping systems considered. Similarly, PCBPC-CT was the eco-efficient choice among the potato-based production systems. In addition, when the NMP-recommended N rate was replaced by the eco-efficient rate for the vegetable horticulture cropping system, the eco-efficient cropping system shifted from a rotation involving CT to a NT system.