MU agronomist: Plant now, add nitrogen later

COLUMBIA, Mo. – The wettest first quarter of the year since 2008 has delayed nitrogen fertilizer applications and corn planting.

When the rain faucet shuts off, plant first and apply nitrogen later, advises Peter Scharf, University of Missouri Extension agronomy specialist and professor in plant sciences at the MU College of Agriculture, Food and Natural Resources.

“Almost all of the time, the right decision is to plant,” he says. “Delaying planting is more likely to hurt yields than delaying nitrogen application. Research shows that delayed nitrogen application won’t hurt yield. In wet years, delayed nitrogen application will actually help yields.”

Scharf cites research from 2008-2010, years with wet springs like the one we are now experiencing. Over those three years, corn receiving nitrogen fertilizer when it was knee-high out-yielded corn receiving all nitrogen fertilizer at planting by an average of 60 bushels per acre each year. “This is because the nitrogen applied at planting was lost due to wet weather and was not there when the crop needed it in June and July.”

Preliminary data from the Missouri Climate Center at MU indicates a statewide average monthly rainfall of 6.2 inches in April, making it the fourth consecutive month with above-normal precipitation. Total statewide precipitation for the first quarter of 2013 was 16.5 inches, more than 5 inches above normal for the period and the seventh-wettest January through April on record. Some areas of northeastern Missouri had as much as 9.2 inches of rain over the last four-week period, pushing corn planting back to 27 days behind last year and 18 days behind normal, according to the May 6 USDA crop progress report.

Delayed application may mean changing machinery. Some producers may have planned to use nitrogen-application equipment before planting that won’t work in a standing crop. Scharf encourages producers to be flexible about how they get their nitrogen applied. He notes that a number of fertilizer dealers have recently purchased or leased high-clearance applicators, and many have side-dress units available. “This creates options in addition to equipment that the producer actually owns.”

Due to drought, much of the nitrogen fertilizer applied to corn last year was not used. Some producers may have hoped to use this nitrogen with another corn crop planted this year. This possibility looked reasonable all through the fall of 2012, but is questionable now. A small number of deep soil samples Scharf and others took this spring have revealed less nitrogen than expected.

“We found almost zero nitrate in the top foot, but about 20 pounds of nitrogen per acre as nitrate in the second foot and another 20 in the third foot,” Scharf said. “In short, the nitrate has moved down, and it seems likely that a good bit has moved below 3 feet deep. I wouldn’t take a credit for last year’s nitrogen unless it was backed up by a deep soil test.”

Soil tests to measure residual nitrogen are available through the MU Soil and Plant Testing Laboratory, through local extension centers or through commercial vendors.

For information on how to interpret soil test results, MU Extension guide G9177, “Preplant Nitrogen Test for Adjusting Corn Nitrogen Recommendations,” is available for free download at extension.missouri.edu/p/G9177.

Nitrogen application also is discussed in “Best Management Practices for Nitrogen Fertilizer in Missouri” (IPM1027), available at extension.missouri.edu/p/IPM1027.

Information also is available from Scharf at plantsci.missouri.edu/nutrientmanagement. Precipitation maps are available at the link for “N Watch 2013,” a tracking tool begun in 2009 to help producers make assessments about nitrogen loss in certain regions of the state.