Anhydrous Ammonia Timing and Rate Effects on Maize Nitrogen Use Efficiencies

Current guidance and equipment technologies permit anhydrous ammonia (NH₃) to be confidently placed parallel to crop rows in both before- and after-planting situations at shallower depths than traditional applications. Field studies from 2010 to 2012 investigated the effects of pre-plant vs. side-dress NH₃ at four N rates (0, 90, 145, and 202 kg N ha–¹) on maize (Zea mays L.) grain yield (GY), N recovery efficiency (NRE), and N use efficiency (NUE). All NH₃ was injected to a 12-cm depth; pre-plant NH₃ was banded parallel to, but approximately 15 cm offset from, intended rows a few days before planting. Side-dress NH₃ was applied to mid-row positions at the V6–V7 growth stage. Whole-plant N uptake at maturity was consistently higher with pre-plant application. Highest GY was observed at the highest N rate with side-dress timing in 2011 but with the pre-plant timing in 2012. Relative to side-dress, pre-plant application improved average NRE across N rates from 0.53 to 0.72 kg plant N kg–¹ applied N during the 3-yr period. Overall NUE levels in 2012 were 50% lower than in 2010 and 40% lower than in 2011 due to drought, yet NRE doubled and NUE more than tripled with pre-plant relative to side-dress application. This 3-yr study highlights the inability of either one-time NH₃ application strategy investigated to consistently have the highest GY and NUE as well as the dominating year-specific influences of both N timing and N rates on NRE.