Nitrogen (N) management strategies that maintain high crop productivity with reduced water quality impacts are needed for tile-drained landscapes of the US Midwest. The objectives of this study were to determine the effect of N application rate, timing, and fall nitrapyrin addition on tile drainage nitrate losses, corn ( L.) yield, N recovery efficiency, and postharvest soil nitrate content over 3 yr in a corn-soybean [ (L.) Merr.] rotation. In addition to an unfertilized control, the following eight N treatments were applied as anhydrous ammonia in a replicated, field-scale experiment with both corn and soybean phases present each year in Illinois: fall and spring applications of 78, 156, and 234 kg N ha, fall application of 156 kg N ha + nitrapyrin, and sidedress (V5-V6) application of 156 kg N ha. Across the 3-yr study period, increases in flow-weighted NO concentrations were found with increasing N rate for fall and spring N applications, whereas N load results were variable. At the same N rate, spring vs. fall N applications reduced flow-weighted NO concentrations only in the corn-soybean-corn rotation. Fall nitrapyrin and sidedress N treatments did not decrease flo8w-weighted NO concentrations in either rotation compared with fall and spring N applications, respectively, or increase corn yield, crop N uptake, or N recovery efficiency in any year. This study indicates that compared with fall N application, spring and sidedress N applications (for corn-soybean-corn) and sidedress N applications (for soybean-corn-soybean) reduced 3-yr mean flow-weighted NO concentrations while maintaining yields.

To meet sustainable intensification goals in the US Midwest, strategies which maintain or increase yields while minimizing negative impacts on water quality are needed. In this study maize yield response and potential nitrogen (N) leaching losses were simultaneously quantified to test the hypothesis that N rates which produced maximum yields would result in minimum yield-scaled N leaching potential. Field experiments were conducted at two sites in 2015 and 2016 to determine the effect of N rate (0, 79, 179, 269, kg N ha −1) on yield, crop N uptake, potential N leaching losses, and post-harvest soil N concentrations. Results show that a significant yield response (up to 179 kg N ha −1) occurred in all years compared to the control. Nitrogen leaching potential increased at 269 kg N ha −1 compared to the control in 2015 but not 2016. Yield-scaled N leaching potential was not statistically different among treatments in three of four site-years. There was no improvement in crop N uptake or N recovery efficiency for 269 kg N ha −1 compared to 179 kg N ha −1 in three of four site-years, which coincided with a trend of increasing post-harvest soil N concentrations, further escalating the risk of environmental N losses. These results did not support our hypothesis that yield-scaled N leaching potential is minimized at N rates that optimize yields (on a normalized basis yield-scaled N leaching potential increased by 28% compared to the control). However, normalized data indicate that 179 kg N ha −1 , the N rate most closely aligned with current recommendations in this region, resulted in 96% of maximum yield while preventing a 25% increase in yield-scaled N leaching potential compared to 269 kg N ha −1 , underscoring the potential for achieving high yields while avoiding increased N leaching potential on an environmental efficiency basis.

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.

Phosphorus fertilizer is frequently fall-applied for corn (Zea mays L.). Diammonium-(DAP) or monoammonium-phosphates (MAP) are the preferred P fertilizers and the N in MAP and DAP is assumed to be available for corn. Our objective was to evaluate the eff ect of application time on availability of ammoniated-phosphate N to the crop in two diff erent environments. In a laboratory study, MAP and DAP at rates of 70 and 140 mg N kg −1 soil were incubated at either 80 or 120% fi eld capacity (FC). Nitrifi cation proceeded rapidly in all treatments, but nitrate levels fell to near zero by 8 wk at 120% FC while remaining above 50% aft er 16 wk at 80% FC. In a 3-yr study at Waseca, MN and Urbana, IL with a factorial combination of three N sources [DAP, MAP, ammonium-sulfate (AMS)], two application times (fall, spring), and two N rates (45, 90 kg N ha −1 ), N rate and application time, but not N source, aff ected grain yield and inorganic soil-N concentrations. Yields were 0.71 and 0.37 Mg ha −1 greater for spring than fall applications at Urbana and Waseca, respectively. Late May soil-N recovery ranged from 31 to 35 and 90 to 100% for fall and spring applications, respectively. It thus appears that only about one-third of N applied in the fall as ammoniated phosphates at typical rates is available to the next year's corn crop in Corn Belt mollisols. Colder, drier fall to spring conditions may increase this proportion, while warmer, wetter conditions would be expected to lower availability.

Artificial subsurface drainage is essential to sustain crop production in many areas but may also impair water quality by exacerbating nitrate (NO 3 )-nitrogen (N) delivery downstream. Cover crops and split-N application have been promoted as key conservation practices for reducing NO 3 -N losses, but few studies have simultaneously assessed their effect on water quality and crop productivity. A field study was conducted to evaluate the effects of N application timing and cover crops on subsurface drainage NO 3 -N losses and grain yield in continuous corn (Zea mays L.). Treatments were preplant-N: 224 kg N ha -1 split-applied with 60% fall + 40% preplant in 2018, or as single preplant applications in 2019 and 2020; split-N: 40% preplant + 60% side-dress (V6-V7); split-N + cover crop (CC): Split-N + cereal rye (Secale cereale L.); and a zero N plot as the control. Across the 3-yr study period, split-N + CC significantly reduced flow-weighted NO 3 -N concentration and NO 3 -N loss by 35 and 37%, respectively, compared with preplant-N. However, flow-weighted NO 3 -N concentration (4.3 mg L -1 ) and NO 3 -N loss (22.4 kg ha -1 ) with split-N were not significantly different from either preplant-N (4.8 mg L -1 and 26.4 kg ha -1 , respectively) or split-N + CC (3.1 mg L -1 and 16.7 kg ha -1 , respectively). Corn yield was significantly lower in the control treatment but did not differ among N fertilized treatments in any year. These results indicate that combining split-N application with cover crops holds promise for meeting the statewide interim milestone NO 3 -N reduction target of 15% by 2025 without negatively impacting crop productivity.