Spring preplant soil profile sampling near the time of crop planting can sometimes give the best indication of the amount of nitrate-N in the soil profile that might carry over to a corn crop, notes Sawyer. This certainly is the case this spring. If you still consider that there could be elevated nitrate-N levels in fields from last year's drought-damaged corn, and the field will be planted to corn again this year, sampling is the best approach to determine if a nitrogen amount can be subtracted from the normal application rate.
Profile sampling is most viable for the northwest area of Iowa where rainfall has been about normal this spring, he adds. You can refer to the previous article published February 21, 2013, on ISU's ICM News website to find suggested sampling procedures.
So the question now is, how much nitrogen should you apply for 2013 corn?
From the soil nitrate samples collected so far this spring, it is clear that the carryover nitrate-N moved deeper into the profile or was lost to tile flow, he explains. With the cold soil temperatures this spring, it is unlikely nitrate was lost by denitrification. Reports from stream monitoring are indicating increased nitrate-N concentrations, as would be expected where tile drainage contributes significantly to stream flow. In many fields, the change in soil profile nitrate-N from last fall is quite dramatic, and unfortunately this means less opportunity to account for nitrate-N carryover for 2013 corn crops.
However, some fields still have carryover nitrate-N amounts that should be used to adjust nitrogen application rates, says Sawyer. "The precipitation maps accompanying this article are quite reminiscent of rainfall patterns of just a few years ago, and we know that in high rainfall years response to applied nitrogen is large, due to loss of soil derived mineralized N, carryover nitrate, and applied fertilizer and manure nitrogen. We'll see if this weather pattern continues for 2013."
CONCLUSION: With the overall wet spring and decrease in carryover profile nitrate, Sawyer suggests farmers consider applying near normal nitrogen application rates for 2013 corn. He recommends farmers use ISU's online Corn Nitrogen Rate Calculator for suggested rates.
Post-Drought Soil And Fertility Issues. Just what has the drought left behind for the 2013 crop? And what steps do you need to take to get land ready for planting? Download our FREE report, 5 Post-Drought Strategies For A Better 2013.