Assessing the Residual from Fertilizer Nitrogen Applied to Failed Corn on the Following Wheat Crop

In much of the Midwest in 2012, extreme hot and dry conditions reduced crop yields, especially corn (Zea mays L.) (USDA-NAAS, 2013). Drought-induced, low-yielding conditions likely resulted in low nitrogen uptake by the crops and the potential for unused fertilizer N left in the soil. However, the potential carryover of unused N fertilizer is uncertain because of the dynamics of N cycling. In 2012, a study was initiated to determine the effect of N rates and nitrification inhibitors on no-till short-season corn. The study was conducted at the Kansas State University Southeast Agricultural Research Center on a Parsons silt loam, a typical claypan soil of the area. The experimental design was a split-plot arrangement of a randomized complete block with four replications with N rates as the whole plots and nitrification inhibitors as the subplots, plus an untreated control. All N was subsurface banded (knifed) as urea-ammonium nitrate (28% N) at a 4-inch depth on 10 Apr. 2012 at rates of 60, 120, 180, and 240 lb/acre. In addition, the knife blades without fertilizer were passed through the no-N control plots. The nitrification inhibitors were (i) none, (ii) Instinct at 35 oz/acre, (iii) Koch experimental at 128 oz/acre, and (iv) Koch experimental at 256 oz/acre. Partially because of replanting in early May, corn growth before silking and during much of the reproductive growth fell in a period from 22 June to 4 Aug. 2012 with total rainfall of 0.75 inches and average maximum air temperature of 99.4°F which is less than 20% of the rain and approximately 10°F hotter than the 30-year average. These conditions resulted in corn yields less than 27 bu/acre with no response to nitrification inhibitors and a slight decline in yields as N rate increased (data not shown). A typical rotation of the area is to follow corn with winter wheat (Triticum aestivum L.). Since the 2012 experiment would not be repeated, the corn crop was followed with a hard red winter wheat cultivar, ‘Everest’ drilled on 12 Oct. 2012 with no added fertilizer and no tillage. To study the residual effect of the N treatments, the same plots with the same experimental Published in Crop Management DOI 10.2134/CM-2014-0005-BR © 2014 American Society of Agronomy and Crop Science Society of America 5585 Guilford Rd., Madison, WI 53711