If you're like most Iowa row crop farmers, you've probably looked out the machine shed door and noticed that it's raining. That's only part of the story today. The rest is what this means with regard to soil nitrates, which you're probably counting on for your corn crop this year (when you can finally get into the fields to plant it).
With heavy rains soaking Iowa this past week or two, farmers are wondering how much of the nitrate-nitrogen that carried over from last year's drought-reduced crop will still be in the fields for this year's corn to use. Mick Lane, communications director for the Iowa Soybean Association's On-Farm Network, with the help of the network's staff, pulled together the following information to help answer that question and other questions farmers have about nitrogen this spring -- now that the weather has suddenly shifted from too dry to "it's getting way too wet."
In a number of fields, there is a lot of nitrogen that hasn't been applied yet, due to the wet weather keeping applicators out of fields so far this spring.
Are heavy rains in April washing away the carryover N from last year?
The Iowa Soybean Association Environmental Programs and Services group routinely monitors water flowing from three tile lines that empty into a creek that flows into the Upper Boone River. Along with the increased water flow that's come with the rain, the nitrate content of the water in two of these lines has jumped from 25 to 30 mg/L (parts per million) in March to more than 40 ppm earlier this week, as shown in the accompanying graph titled "Hamilton County Tile Main Nitrate-N."
What this suggests is a lot of nitrates are being flushed out of the soil and into flowing water. Odds are this is happening in most of Iowa, not just in the Boone River Watershed. It doesn't matter whether the nitrate was left in the soil after last year's drought-reduced corn crop, or if it is from mineralization of soil organic matter, or if it is coming out of what you've applied for the 2013 corn crop. What matters is it won't be there for the crop you're about to plant.
Post-Drought Soil And Fertility Issues
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