Estimating N mineralization in a dry year

A soil nitrate test is an excellent way to measure nitrogen mineralized from the soil over the spring. The test offers a window into the temperature and moisture mix of a particular season to-date and helps inform the critical side-dress N amount on corn.

Dale Cowan, senior agronomists with AGRIS Co-op, pulled nitrate tests from three different cropping systems for comparison and is now setting out to set side-dress targets.

Perhaps surprising and definitely disappointing are results from a field that received biosolids in August of 2022.

“That was supposed to provide 220 pounds of plant-available nitrogen to the following crop, and the only problem with that is the following crop was this May of 2023. So it was a long time in between,” Cowan says. “The nitrate soil tests that we did take, came back still recommending around 95 to 100 pounds of nitrogen.”

Where did the N go? Either it mineralized or leached, Cowan says, which may surprise some people, seeing as last year was dry. But we did achieve soil recharge of sub-soils over the winter, and that means some water movement through through the soil.

Either way, this is a scenario where the farmer was counting on not using a lot of commercial N, but will still need to to meet the corn crop’s needs.

Overall, this year has been cool and dry, leading to less than average N mineralization, Cowan says. Unlike last year where some crops pulled off impressive yields on low added fertility, this may be the year where side-dress rates need bumped up.

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