Response of Wheat to Residual N after Drought-Stressed Corn.

When drought conditions result in poor corn growth and yield, the potential exists for carry-over of fertilizer N to a following wheat crop.  A study was started in 2012 to determine the effect of N rates and nitrification inhibitors on short-season corn grown with no tillage.  Replanting the corn in early May placed much of the reproductive growth during extreme hot, dry weather resulting in corn yields less than 1.9 Mg/ha with no response to nitrification inhibitors and a slight decline in yields as N rate increased.  Since the 2012 corn experiment would not be repeated, wheat was drilled in the fall with no added fertilizer and no tillage. The same plots were used to study the residual effect of the N treatments.  The use of nitrification inhibitors on the previous corn crop had no residual effect on the soil inorganic N levels and wheat NDVI (normalized difference vegetative index) readings taken in early April or wheat yield in June 2013.  However, the residual from the previous N rate treatments did affect soil NO₃-N and NDVI readings at jointing and wheat yields, but not soil NH₄-N levels in the top 30 cm, which were about 21 kg N/ha.  Slight increases in soil NO₃-N levels as previous N rate increased up to 268 kg N/ha did not appear sufficient to account for the more than 1 Mg/ha wheat yield increase.  The relationship between wheat NDVI measurements at jointing and wheat yield was linear.  Preplant fertilizer N applied to corn that was later stricken by drought can affect subsequent wheat yield; however, inorganic soil N may not always be a reliable indicator of residual N effect on subsequent wheat yield.  Differences in NDVI measurements of wheat made at jointing appear to be a good indicator of differences in final yield.