The On-Farm Network tests cornstalks for nitrate content before harvest each fall in a number of locations in Iowa. This end-of-season cornstalk nitrate test gives you an idea as to how much carryover nitrogen might be in the soil for the next year's crop. In 2012, a drought year that reduced yields considerably, you would expect more N to carryover in the soil for the 2013 crop since the low-yielding 2012 crop didn't use as much N as it otherwise would if yields were higher.
Last year's On-Farm Network end-of-season stalk nitrate testing program showed considerably higher stalk nitrate levels than in the previous six years, with 45% of the samples collected in the "excessive" range. See the second graph accompanying this article.
A reasonable guess is that drought-stricken corn plants were able to take up more nitrogen than they were able to put into grain production. A portion of the nitrate from last year's higher-nitrate stalks, now on the soil surface or mixed into soil by tillage, will be mineralized by soil microbes and available to crops this year. How much of this N will be available and when depends on a host of factors, including soil temperature and moisture.
This situation brings up some very important nitrogen management questions
1) What's the status of nitrogen currently in the soil? Is there residual N left over from last year's crop? How much of the fertilizer nitrogen applied last fall or earlier this spring will still be there when the 2013 corn crop is finally ready to use it?
2) Is there anything a farmer can do to assure that his/her 2013 corn crop has adequate N?
A late spring (pre-sidedress) soil nitrate test can help you answer these questions. If all, or the majority, of your N fertilizer was applied before planting, the soil nitrate level from the late spring soil nitrate test can provide a guide for determining whether additional nitrogen fertilizer may be necessary to avoid a shortage for the corn plants later this summer.
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.