|Timing of spring nitrogen application is important|
|Thursday, April 11, 2013 12:14 PM|
Assistant Professor OSU-Extension Educator
Fall N applications are usually less effective than spring applications. In general, fall-applied N is 10 to 15 percent less effective than N applied in the spring. Higher N application rates should not be used in the fall to try to make up for potential N losses. Use of a nitrification inhibitor with fall-applied N can improve the effectiveness of these treatments. Most studies show, however, that spring-applied N is more effective than inhibitor-treated fall N when conditions favoring N loss from fall applications develop. Inhibitor-treated anhydrous ammonia was superior to anhydrous ammonia when applied in the fall, but not when applied in the spring. Spring-applied anhydrous ammonia, however, was on the average better than the fall inhibitor-treated ammonia. To increase the effectiveness of fall-applied N with an inhibitor, delay the application until soil temperatures are below 50 degrees F.
Benefits from delayed or sidedress N applications are most likely where there is a high risk of N loss between planting and crop N use. Preplant N losses occur from sandy soils through leaching and from poorly drained soils through denitrification. For medium- and fine-textured soils, yields seldom differ between preplant and sidedress application. Occasionally, sidedress application can be superior to preplant application when early season rainfall is excessive. The advantage to delaying N application is to assess crop needs based on soil moisture and crop conditions. The disadvantages of delaying the major fertilizer N application are: the crop may have been under N deficiency stress before fertilizer N is applied, resulting in a yield loss; wet conditions during the sidedress application period can prevent application, and later additions may not be possible because of corn growth; and dry conditions at and after sidedressing will limit N uptake.
John Sawyer, Iowa State University Extension Soil Fertility specialist says, “In a wet spring or a wet early summer, sidedressed N should perform better than N applied preplant, because there is typically less N-loss associated with sidedressing,” he says. “In contrast, preplant N applications typically work better when conditions are dryer-than-normal during spring and early summer or equally as well with sidedress when conditions are normal.”
“Sidedressing is typically better for poorly drained soils or sandy, or excessively drained soils, where there’s more risk of N loss,” Sawyer says. “For moderate to well-drained, fine-textured soils, that don’t tend to pond, the N-loss risk is lower, and preplant N applications can perform equal to or better than sidedressed applications.” (Taken from Corn and Soybean Digest, 2010.).
Sebastian Braum, a Yara North America agronomist says farmers who are able to sidedress 32% urea-ammonium nitrate (UAN) solution will likely garner the best value for their dollar. “Sidedressing 32% UAN is a good hedge against N loss, especially if you anticipate a cool, wet spring,” he says. “Good managers know that they’ll get the best performance out of their N dollars if they split-apply. So, I would recommend putting half your N down pre-plant as close to planting as possible and half your N down after planting. If you sidedress anhydrous ammonia, stay within the rows or you’ll burn the roots and it takes longer for the N to become available to the corn than 32% UAN, which becomes available to the crop immediately,” (Taken from Corn and Soybean Digest, 2010.)