'Pipes & Valves': Managing crop production and environmental impact by mitigating ammonia, nitrous oxide, and nitrate losses

Context: Canada has targeted a 30% reduction in N2O emissions from fertilizer by 2030 in its commitments to reduce greenhouse gas emissions. To help achieve these commitments, a 'Pipes & Valves' conceptual visualization of the DNDC model was combined with the DeNitrification-DeComposition (DNDC) model to evaluate a suite of nutrient management and conservation practices. Objectives: The objectives were to meet the 30% reduction targets in N2O emissions as well as other reactive-N species (N2O, NI-13 and NO3- leaching) to provide a systems approach while increasing corn yields. This was accomplished by: 1) developing a 'Pipes & Valves' conceptual visualization model; 2) evaluating a full system DNDC model with 3-years of NI-13 volatilization, N2O emission, inorganic N, crop yield and N uptake data; 3) applying the 'Pipes & Valves' DNDC system to identify N-management strategies that mitigate N-loss and improve yields. Methods: The DNDC model compared simulated and measured N-loss and crop performance over 3 years for Nmanagement practices including pre-plant versus side-dress UAN injection with either no inhibitors, a urease inhibitor or a dual urease and nitrification inhibitor. A Pipe and Valves conceptual visualization model was developed and used with the DNDC model to simulate 14 management scenarios based on moldboard plow tillage versus conservation tillage, and fertilizer management including fertilizer type (urea vs. urea ammonium nitrate, UAN), inhibitor (none, nitrification inhibitor, urease inhibitor or both), placement (broadcast vs. injection), timing (at planting vs. split application), and N rate (recommended vs. 15% reduction). Results: The DNDC model was evaluated using field data and had excellent performance for yields, cumulative N2O emissions and soil temperature while soil water predictions were fair using standard performance metrics. Multiple nutrient management and/or conservation tillage practices decreased NI-13 losses by 36-96% compared to broadcast urea. A pre-plant broadcast urea and nitrification inhibitor treatment and a conservation tillage treatment with side-dressed injected UAN with a dual urease and nitrification inhibitor reduced N2O losses by 37-40%. Conclusions: Although several management practices reduced one N-loss pathway by >= 30%, only side-dress injected UAN with urease plus nitrification inhibitors under conservation tillage achieved multiple reductions of 40%, 93% and 62% in N2O, NI-13 and reactive-N, respectively while increasing corn grain yields by 7%. Significance: Combining the 'Pipes & Valves' conceptual visualization model with DNDC modelling was effective for determining how 4R nutrient management and conservation tillage can be stacked and used worldwide to meet N-loss reduction targets without compromising yields.