By Susan Jongeneel
Courtesy of University of Illinois
Corn is growing rapidly, so you may want to apply nitrogen soon
While soil temperatures were warmer than normal last winter, the dry soil conditions have resulted in very little nitrogen loss this spring.
According to assistant professor of crop sciences Fabian Fernandez, soils in the state were dry at the beginning of autumn 2011, with above-average precipitation levels only during November and December.
"In March, I predicted that the risk of nitrogen loss would increase only if the spring became too wet," Fernandez said. Precipitation so far this year is below average in the state. Thus, so far, the likelihood of nitrogen loss this year is very low.
Taking a look at soil nitrogen also provides evidence that applied nitrogen remains in the soil.
"Nitrification has proceeded quickly this spring," Fernandez said. In central Illinois, a field with anhydrous ammonia plus NServe applied in November 2011 contained 80 ppm ammonium in the top 12 inches of soil at the end of February. Now, in mid-May, the concentration is 27 ppm. During the same time interval, nitrate concentrations have increased from 10 to 31 ppm. Although ammonium has transformed to nitrate, there is still a considerable amount of ammonium in the soil, probably because not all of it has been nitrified and also because organic nitrogen in the soil is being mineralized to ammonium.
Last week, samples were also collected for the 12- to 24-inch depth. As expected, there has not been sufficient water to move nitrate down the profile and nitrogen concentrations were low: soil nitrate was only 9 ppm and soil ammonium was 3 ppm.
At this time, most corn is growing rapidly and starting to take up nitrogen. "If all the nitrogen has already been applied, I do not anticipate a need to apply additional nitrogen for this crop," Fernandez said. "If no nitrogen or only a portion of the nitrogen was applied, now is the time to start applying the balance of the application."
The nitrogen needs of the corn plant are low from the early vegetative development stages until about V5 (fifth-leaf stage). Most nitrogen is taken up during the V8 to VT (tassel) stages. Soon after pollination, nitrogen uptake is essentially completed.
Because the potential for nitrogen loss by leaching or denitrification at this time of the growing season is very low and corn plants will soon enter a rapid nitrogen uptake phase, Fernandez recommends not delaying the application. However, if farmers are not quite ready, research has shown that the chance for yield loss due to nitrogen stress is very low, even when applications are done as late as the V6 development stage, because in most soils in Illinois, mineralization of soil organic nitrogen provides ample nitrogen for early crop demands. Moreover, if part of the total nitrogen was already applied, a delay in applying the remaining nitrogen is not likely to cause plant nitrogen stress.