Consequences Of "Shallow" Pre-Plant Anhydrous Ammonia Placement On Corn Production.

Few studies have investigated consequences of alternate methods of anhydrous ammonia (NH₃) fertilizer placement in multiple tillage systems on corn (Zea mays L.) growth and plant N responses. Field studies were conducted between 2010 and 2012 near West Lafayette, IN to compare two "shallow" pre-plant NH₃ placements (diagonal to the row vs. parallel but 15-cm offset from the row) in no-till and conventional tillage systems at different nitrogen (N) rates (145 and 202 kg N ha^-1). Corn was planted with additional starter N (20 kg N ha^-1) within 6 days of NH₃ application. Diagonal NH₃ application placement never resulted in significant corn seedling mortality. Conventional tillage increased mean grain yields by ~1 Mg ha^-1. Tillage did not impact reproductive-stage leaf chlorophyll content (SPAD), or grain N content, when NH₃ was parallel-applied, but the same plant responses were significantly lower in no-till after diagonal NH₃ application. Parallel NH₃ application increased grain N concentration in 2010 compared to diagonal NH₃ placement. Lowering the N rate to 145 from 202 kg N ha^-1 significantly lowered corn biomass production, grain N, and whole-plant N accumulation in 2010 and 2012 when NH₃ was diagonally applied, but not when NH₃ was parallel applied. The benefit of parallel, relative to diagonal, placement at the lower N rate, and in no-till, was also evident in higher leaf SPAD during grain filling. The potential for lowering N rates, without yield penalty, with "shallow" pre-plant NH₃ application is more likely via parallel placement to corn rows than with diagonal application.