Evaluation of Midseason UAN Application Depth in Winter Wheat

Abstract

Nitrogen Use Efficiency (NUE) is estimated to be only 33% for cereal production in the world. Providing producers with efficient methods to increase the effectiveness of their Nitrogen (N) applications is integral to agricultural sustainability and environmental quality. This study was conducted to evaluate the effect various subsurface placement depths of urea ammonium nitrate (UAN) has on grain yield, plant N uptake and NUE in winter wheat. Liquid UAN was applied in bands at depths of 5 and 10 cm, along with surface applications, all at various N rates at Feekes growth stage 5. Fields under conservation tillage at low N rates benefited from subsurface applications. No-till soils experience a shift in the active microbial zone compared to conventionally tilled fields, resulting in greater rates of N immobilization from N applied in the upper 6-7 cm of the soil profile. Conventional tillage generally benefits from subsurface applications, specifically when weather and environmental conditions are present that promote ammonia volatilization following fertilizer application. Nitrogen rates that provide the greatest economic returns are dependent on the environment, as yearly environmental variability is difficult to predict. Subsurface application depths of 10 cm provided notable increases in NUE compared to surface applications. Treatments at depths of 5 cm provided several instances of increased grain N. With a few instances of exception, UAN subsurface application depths had limited impact on grain yield, and were similar to that of surface applied N. Application depths of 10 cm had the greatest impact on grain yield in no-till cropping systems at low N rates.