Strategies to limit (minimize) nitrogen leaching on dairy farms driven by seasonal climate forecasts

Dairy farmers in Florida are required to limit nitrogen leaching into the ground water below 10 mg L−1. Literature shows that nitrogen leaching on a dairy farm varies greatly with forage systems, amount of manure N applied, seasonal rainfall amounts, and soil characteristics. The purpose of this study was to devise dairy-specific strategies for forage crops and manure effluent application rates conditioned to the El Niño Southern Oscillation (ENSO) phenomenon that determines El Niño, La Niña, or neutral years, each of which is associated with temperature and rainfall patterns, to reduce N leaching on a typical North Florida dairy farm. The Decision Support System for Agrotechnology Transfer (DSSAT) was used to simulate N leaching and biomass accumulation using 43 years of daily weather data and eleven forage systems supplied with four levels of manure N (20-160 kg N ha−1 mo−1), and ten soil types where dairies are found. Higher N leaching and lower biomass accumulation occurred in El Niño years than in neutral and La Niña years. N leaching in all ENSO phases was high in winter, particularly in January and February compared to other times in a year. Overall, forage systems with the best potential to limit N leaching were: in the spring (March-May) those that combine bahiagrass or bermudagrass in El Niño years and corn in neutral and La Niña years; in the summer (June-August) those with bahiagrass or bermudagrass in El Niño, bahiagrass, bermudagrass, or corn in neutral, and corn in La Niña years; and in the winter (December-March) those with intercropping of ryegrass, rye, oats, and wheat. This study demonstrates that recommendations for least N leaching can be developed using ENSO phase forecasts.