Corn (Zea mays L.) production in poorly drained claypan soils in the US Midwest is a challenge due to low soil permeability, which may result in wetter soil conditions and relatively large amounts of soil N2O emissions early in the growing season. The objectives of this study were to determine the effects of urea fertilizer placement with and without nitrapyrin (NI) on daily and cumulative soil N2O emissions, and yield‐scaled N2O emissions in 2016 and 2017. Treatments included urea deep banded to a 20‐cm depth (DB), urea deep banded to 20 cm plus NI (DB+NI), urea incorporated after a surface broadcast application to ∼8‐cm depth (IA), urea broadcast on the soil surface (SA), and a nonfertilized control (NTC). Fertilizer was applied at 202 kg N ha−1. Surface soil N2O efflux rates were generally lower (<50 g N2O‐N ha−1 d−1) during the first 3 wk after N fertilization and latter parts of the growing seasons. When averaged across the 2016 and 2017 growing seasons, all fertilized treatments had significantly greater (2.33–5.60 kg N2O‐N ha−1, P < 0.05) cumulative soil N2O emissions than NTC. The DB+NI treatment had 54 and 55% lower cumulative soil N2O emissions than IA and SA, respectively. In 2017, DB+NI had similar soil yield‐scaled N2O emissions to NTC. Percentage grain yield increase over NTC was highest for DB and DB+NI. Grain yield in 2016 was 14 to 18% higher for DB and DB+NI than SA. Results suggest that DB+NI is an effective management strategy for reducing cumulative soil N2O emissions and increasing grain yields over the growing season. Core Ideas Deep‐banded urea + nitrapyrin had 55% less soil N2O emissions than surface‐applied. Nonfertilized control and deep‐banded urea + nitrapyrin had similar N2O emissions. Deep‐banded urea + nitrapyrin had a 1.6% lower emission factor than surface‐applied urea. Deep‐banded urea had a 1.0% lower emission factor than surface‐applied urea.

Agronomic efficiency (AE) and apparent N recovery efficiency (RE) can be improved by developing more effective N fertilizer placement strategies; however, minimal research has focused on poorly‐drained claypan soils which are prone to saturated conditions and gaseous N loss. The objective of this 2‐yr study was to determine the effectiveness of different N fertilizer placement methods on corn (Zea mays L.) grain yield, grain quality, silage yield, N uptake, AE, RE, and spatial soil N distribution over time. Nitrogen placement treatments included deep‐banded urea (DB) or urea plus nitrapyrin (DB+NI) at a depth of 20 cm compared to urea broadcast applied (BC) or BC incorporated to a depth of 8 cm (BCI). The DB and DB+NI treatments generally resulted in higher grain and silage yields than the non‐treated control (NC), BCI, and BC treatments. The DB+NI increased silage yield 4.14 to 4.77 Mg ha−1 over the BC and DB treatments in 2016. Additionally, DB+NI resulted in 21 and 27% greater N uptake and RE than other N placement treatments. Deep‐banded treatments with and without NI had the highest AE (10.3–13.3 kg kg N−1) compared to other treatments. Deep‐banded urea had significantly higher soil NO3–N concentrations in deep soil layers compared to DB+NI when sampled in July. Results indicated DB+NI increased N availability for a longer period during the growing season and was a reliable strategy for increasing corn yields and improving AE and RE on a poorly‐drained claypan soil. Core Ideas Yield response to urea was ranked DB+NI = DB > BCI > BC. Apparent N recovery efficiency was greatest (76.5%) with DB+NI. Highest agronomic efficiency (10.3 to 13.3 kg kgN−1) was observed for DB and DB+NI. Distribution of pHs, NO3‐N, and NH4‐N in the soil was affected by urea placement.

Claypan soils have a high potential for N loss, which can lower corn (Zea mays L.) yields. Field research was conducted from 2011 to 2013 in Northeast Missouri to determine corn yield, plant population, and grain quality response to N application timings (fall vs. spring) and five N sources/placements at two different N rates (84 and 168 kg·N·ha−1) on a poorly drained claypan soil. The five N source/placement systems were no-till (NT)/surface broadcast urea ammonium nitrate (UAN) (Surface UAN) or strip-till (ST)/deep banded UAN (deep UAN), NT/surface broadcast UAN plus Nitamin Nfusion (surface NF) or ST/deep banded UAN plus Nitamin Nfusion (deep NF), and ST/deep banded anhydrous ammonia (AA) (deep AA). The field trial was a split-plot randomized complete block design with four replications. Deep UAN with a fall N application produced the highest grain yield (8.12 to 9.12 Mg·ha−1) at 84 and 168 kg·N·ha−1, but it was less effective with a spring application in 2011. Fall deep AA produced the lowest grain yields (5.97 and 6.8 Mg·ha−1) in 2013 at 84 and 168 kg·N·ha−1 potentially due to wet soil conditions at the time of application. Warmer and wetter soil conditions during April-May of 2013 resulted in relatively higher grain yields compared to cooler and drier soil conditions in 2011 with all spring-applied N source/placement treatments. Extreme drought in the 2012 growing season resulted in poor corn growth. Farmers may need to consider fall N applications on claypan soils because spring N application might be riskier since corn grain yield was generally greater than or equal to spring-applied treatments.