Effect Of N Source, Method and Timing Of Application, and Irrigation On Corn In a Water Limited Environment.

Introduction

With the demand for corn increasing, production has spread into more water limited, semi-arid regions. Couple this with increasing nitrogen (N) fertilizer costs and environmental concerns, the need for proper N fertilizer management practices has increased. The objective of this experiment was to evaluate the effect of N fertilizer sources, method and timing of application, and irrigation on corn grain yield, grain N content, N use efficiency (NUE), and water use efficiency (WUE). The experiment was arranged as a randomized complete block design with replication and fertilizer treatments nested within irrigated or rain-fed sites. Fertilizer treatments consisted of two N rates (90 and 180 kg N ha^-1) of ammonium sulfate (AS) and urea ammonium nitrate (UAN) applied preplant or as a split (preplant and V8) application. Mid-season foliar applied N treatments of 45 and 90 kg N ha^-1, split 50/50 at V8 and V10, were also evaluated. The study was conducted at two locations in north-central Oklahoma for both the 2012 and 2013 growing seasons. In 2012, plots fertilized with AS reported higher grain yield, NUE, and WUE, regardless of the site being irrigated or rain-fed. No statistical differences (alpaha=0.05) in grain N were observed based upon N source, but irrigated treatments with N split applied at preplant and V8 had increased grain N content and NUE. Foliar N applications decreased grain N content for both sites and decreased yields on irrigated sites likely due to significant leaf burn. However, foliar treatments did increase grain yield for rain-fed treatments at one location when compared to plots having the same rate of fertilizer applied preplant.  The 2013 growing season was unusually cool and moist for Oklahoma and harvest was delayed, thus the results and conclusions will be presented later.