Abstract:To prevent nutrient limitations to crop growth, nitrogen is often applied in agricultural systems in the form of organic inputs (e.g., crop residues, manure, compost, etc.) or inorganic fertilizer. Inorganic nitrogen fertilizer has large environmental and economic costs, particularly for low-input smallholder farming systems. The concept of combining organic, inorganic, and biological nutrient sources through Integrated Nutrient Management (INM) is increasingly promoted as a means of improving nutrient use efficiency by matching soil nutrient availability with crop demand. While the majority of previous research on INM has focused on soil quality and yield, potential climate change impacts have rarely been assessed. In particular, it remains unclear whether INM increases or decreases soil nitrous oxide (N 2 O) emissions compared to organic nitrogen inputs, which may represent an overlooked environmental tradeoff. The objectives of this review were to (i) summarize the mechanisms influencing N 2 O emissions in response to organic and inorganic nitrogen (N) fertilizer sources, (ii) synthesize findings from the limited number of field experiments that have directly compared N 2 O emissions for organic N inputs vs. INM treatments, (iii) develop a hypothesis for conditions under which INM reduces N 2 O emissions and (iv) identify key knowledge gaps to address in future research. In general, INM treatments having low carbon to nitrogen ratio C:N (<8) tended to reduce emissions compared to organic amendments alone, while INM treatments with higher C:N resulted in no change or increased N 2 O emissions.

Core Ideas Enhanced‐efficiency fertilizers reduced N2O compared with anhydrous ammonia in two of three years. SuperU reduced both area‐ and yield‐scaled N2O emissions in two of three years. Soil inorganic N concentrations were not correlated with daily N2O fluxes. Fertilizers ESN, SuperU, and UAN + nitrapyrin did not increase yield or grain N recovery efficiency. Balancing efforts to mitigate nitrous oxide (N2O) emissions from crop production while increasing grain yields is an important challenge for agriculture. The objectives of this study were to assess N2O emissions, soil inorganic nitrogen (N) concentrations, grain yield, and grain N content for three enhanced‐efficiency nitrogen fertilizers (EENFs) compared with anhydrous ammonia in a rainfed corn system in Illinois over 3 yr (2015–2017). Treatments included a control (check) and four N sources applied at 202 kg N ha−1: injected anhydrous ammonia, stabilized urea containing urease and nitrification inhibitors (SuperU, Agrotain International), polymer‐coated urea (ESN, Agrium Advanced Technologies), and injected urea‐ammonium nitrate (UAN) + nitrapyrin. Significant reductions in N2O emissions were observed for several EENFs compared with anhydrous ammonia, but results were not consistent across treatments and years. SuperU reduced area‐ and yield‐scaled N2O emissions in two of three study years compared with anhydrous ammonia, while ESN had no N2O mitigation benefit. Injected UAN + nitrapyrin had the highest emissions in the first year but significantly decreased emissions in the second 2 yr. No treatment significantly improved yield or grain N content compared with anhydrous ammonia. In light of efforts to broadly promote EENFs in the US Midwest, these results demonstrate there is some promise for N2O mitigation, but the lack of clear crop productivity benefits combined with inconsistent N2O mitigation effects do not support the conclusion that EENFs inherently improve agronomic and environmental outcomes.