Anhydrous Ammonia Timing and Rate Effects on Maize Nitrogen Use Efficiencies

Abstract

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.