Keep legumes´ nitrogen credits in mind when topdressing wheat

As producers plan for winter topdressing wheat or another small grain cereal, they should be conservative in the amount of nitrogen (N) credit they count as coming from a preceding legume crop, a Kansas State University agronomist said.

For example, if the small grain is following alfalfa that was destroyed during the summer, producers typically should figure on getting about one-half the N credit that row crops planted the following spring would get, said Dale Leikam, nutrient management specialist with K-State Research and Extension.

“The reason winter cereals get a smaller N credit than would summer row crops in this situation is that there has been less time for the alfalfa residue to decompose and the N to be mineralized,” Leikam said.

“If the alfalfa stand was killed in late fall, rather than summer, it’s best to allow little or no N credit for winter cereals planted into the residue.

“For soybeans harvested only a few days or weeks before wheat planting, we also would expect little N mineralization over the winter. So, no N credit should be given for the wheat in that case, either.”

More information about nutrient management in crops and crop production in general is available at any county or district K-State Research and Extension office, as well as on the Web at http://www.oznet.ksu.edu.

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