Fertilizer Placement Affects Corn and Nitrogen Use Efficiency in a Claypan Soil

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 NO 3 –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, NO 3 ‐N, and NH 4 ‐N in the soil was affected by urea placement.