Site Specific, Weather Adjusted, Real Time Nitrogen Recommendations for Maize: Adapt-N Increased Grower Profits and Decreased Nitrogen Inputs and Losses in Three Seasons of on-Farm Strip Trials.

Dynamic, complex and locally-specific interactions among weather, soil, and management affect N loss, crop-available N in the soil, and crop N uptake. Particularly, differences in early-season precipitation lead to well-documented variability in economic optimum N rates. Uncertainty in N input needs incentivizes high N application rates, which then lead to high environmental losses in the majority of years. The web-based Adapt-N tool (http://adapt-n.cals.cornell.edu) was designed to improve maize N use efficiency by shrinking the uncertainty around the economic optimum N rate at sidedress time. Adapt-N uses near real-time high resolution climate data, and field specific management, soils, and crop information supplied by users via a user friendly web interface, as inputs for a dynamic simulation model (Precision Nitrogen Management model). The model simulates daily soil C and N transformations, soil water storage and transport, and uptake of water and N by the maize crop. The Adapt-N web-interface provides in-season N recommendations, as well as graphs visualizing seasonal dynamics of soil N, crop growth, temperature, and precipitation for each management unit. In collaboration with consultants, extension staff, and growers in the Northeast and Midwest, we compared yield and profit outcomes from Adapt-N recommended rates vs. current grower N rates in replicated on-farm strip trials in grain and silage maize in 2011-2013, with further trials in progress during the 2014 growing season. Data indicate that the model successfully adapted to site-specific weather in 104 trials in NY and IA. N inputs were reduced in over 85% of trials without significant yield loss, and profit increase, after relatively dry springs. N rates were increased over grower rates after relatively wetter springs in the remaining cases, with commensurate yield and profit increases. On average across 104 trials, N application rates were reduced by an average of 41 kg ha^-1 (37 lbs ac^-1), while yields increased by 106 kg ha^-1 (2 bu ac^-1), and profits derived from N savings or increased yields across the trials increased by $94 ha^-1 ($38 ac^-1). Adapt-N provides incentive for better N application timing, by enabling higher N use efficiency and profits, as well as decreased greenhouse gas emissions.