While soil temperatures were warmer than normal last winter, the dry soil conditions have resulted in very little nitrogen (N) loss this spring. According to Assistant Professor of Crop Sciences Fabián Fernández, 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 N loss would increase only if the spring became too wet,” says Fernández. Precipitation thus far this year is, overall, below average in the state. Thus, so far, the likelihood of N loss this year is very low
Taking a look at soil N also provides evidence that applied N remains in the soil.
“Nitrification has proceeded quickly this spring,” Fernández says. In central Illinois, a field with anhydrous ammonia plus NServe applied in November 2011 contained 80 ppm ammonium in the top 12 in. 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 12-24-in. depth. As expected, there has not been sufficient water to move nitrate down the profile and N concentrations were low: soil nitrate was only 9 ppm and soil ammonium was 3 ppm.
At this time, most cornis growing rapidly and starting to take up N. “If all the N has already been applied, I do not anticipate a need to apply additional N for this crop,” Fernández says. “If no N or only a portion of the N was applied, now is the time to start applying the balance of the application.”
The N needs of the corn plant are low from the early vegetative development stages until about V5 (fifth-leaf stage). Most N is taken up during the V8 to VT (tassel) stages. Soon after pollination, N uptake is essentially completed.
Because the potential for N loss by leaching or denitrification at this time of the growing season is very low and corn plants will soon enter a rapid N uptake phase, Fernández recommends not delaying the application. However, if farmers are not quite ready, research has shown that the chance for yield loss due to N 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 N provides ample N for early crop demands. Moreover, if part of the total N was already applied, a delay in applying the remaining N is not likely to cause plant N stress.
In fields with low N-supplying power (soils with low organic matter) or where no N has been applied, early application (before the V6 development stage) is recommended to avoid loss of yield potential. Another reason not to delay application, especially because of the dry conditions this year, is that the sooner N is applied, the greater chance it will have to be moved into the root zone by rain.