As the rains continue into mid-June, so does the talk about nitrogen losses from crop fields. Nitrogen deficiency symptoms in corn plants can be a warning sign of yield limitations to come.
In a presentation at the Western Iowa No-Tillers Field Day near Shelby June 16, Pat Reeg, Iowa Soybean Association On-Farm Network technology manager, told attendees that nitrogen loss and nitrate content in water correlate more directly with rainfall amounts and frequency than with amount of nitrogen applied within a watershed region in any given year.
He says that if sidedressing is part of your normal nitrogen management program and very little of your nitrogen was applied before planting, chances are applying your normal rate of nitrogen fertilizer at sidedressing time will be sufficient for this year's corn crop. That's assuming, of course, that you can actually get into the fields to sidedress! "If you put on most of your nitrogen last fall, or were able to get it on preplant and then see yellowing in corn leaves, using the late spring soil nitrate test can indicate whether there's a need for an extra application of nitrogen," says Mick Lane, research communications manager for the On-Farm Network.
He explained a little about how to use the late spring soil nitrate test in last week's newsletter that is published online by the On-Farm Network. He offers are a few more notes on that topic:
* The critical concentration is 20 ppm in a wet spring.
* Collecting good cores of soil for testing can be a challenge in saturated soils.
* Because Iowa fields are variable, multiple samples should be collected in each field.
* Fields with N applied in a band such as anhydrous ammonia or injected swine manure are difficult to sample. The best way to sample fields that have received banded N is to collect three sets of 8 cores that are positioned at various distances between two corn rows.
* For help with interpreting results, see this On-Farm Network publication and also Iowa State University Extension Publication PM1714.
Other references are also available online to help you with current crop management decisions
If you still have soybeans to plant, see ISA's Soybean Planting Brief issued last week. This article lists several considerations and options for farmers facing planting delays, including a clarification of many of the crop insurance factors, soybean planting dates vs. group maturity selections, soybeans and nitrogen fertilizer, cover crops and the prevented planting option.