Improvements in maize N recommendations decreased carbon dioxide equivalence without sacrificing yield

Globally, agricultural scientists are challenged with creating, testing, and validating climate-smart nutrient strategies that reduce greenhouse gas emissions while increasing food security. This study determined maize (Zea mays L.) N recommendations and bias for N-rate studies conducted in South Dakota using models created for western Minnesota, Iowa, Eastern North Dakota, Nebraska, and South Dakota. From 2019 to 2021, 16 N rate studies were conducted in long-term no-tillage (>6 years) fields located in South Dakota. In the randomized block replicated study, the soils were mollisols that were derived in a semi-arid frigid environment. The economic optimum N rates were calculated using four fertilizer-to-maize grain price ratios (4.11, 5.48, 6.85, and 8.23 [$ (kg N)⁻¹] [$ (kg grain)⁻¹]⁻¹). Analysis showed that reducing the yield goal coefficient used in the South Dakota model from 21.4 to 17.9 kg N (Mg grain)⁻¹ reduced the recommended N rate but did not reduce yield. The reduced yield goal coefficient that considered the fertilizer-to-maize price ratio also reduced model root mean square error (RMSE), bias, and the estimated partial carbon dioxide equivalence (CO_2e) by at least 18%. Nitrogen recommendation models developed for western Minnesota, Iowa, and South Dakota had similar RMSE, bias, and fertilizer recommendations, and adjusting the recommendation based on expected fertilizer cost and maize selling price improved accuracy. This study suggests that yield was not sacrificed by reducing the coefficients from 21.4 to 17.9 kg N (Mg grain)⁻¹ and that recommendations are improved by considering the fertilizer-to-maize grain price ratio.