Michigan State University Extension
Soils & Soil Management - Fertilizer - 06039711
07/10/97
Tri-state Fertilizer Recommendations for Corn, Soybeans, Wheat and Alfalfa Extension Bulletin E-2567 (New), July 1995
M.L. Vitosh, Michigan State University; J.W. Johnson, The Ohio State University; D.B. Mengel, Purdue University; Co-editors
The timing of N fertilizer applications is an important factor affecting the efficiency of fertilizer N because the interval between application and crop uptake determines the length of exposure of fertilizer N to loss processes such as leaching and denitrification. Timing N applications to reduce the chance of N losses through these processes can increase the efficiency of fertilizer N use.
Ideally, N applications should coincide with the N needs of the crop. This approach requires application of most of the N requirement for corn during a period 6 to 10 weeks after planting. Application of N during the period of maximum crop demand may not be practical or possible; other methods and times of application may be equally efficient and appropriate. The efficacy of time of application depends on soil texture, drainage characteristics of the soil, amount and frequency of rainfall or irrigation, soil temperature and, in some situations, the fertilizer N source. Nitrogen timing options usually include fall applications, spring preplant applications, Sidedress delayed applications made after planting, and split or multiple treatments added in two or more increments during the growing season.
Fall vs. Spring Applications
Fall applications of N are feasible only in areas where low winter soil temperatures retard nitrification of ammonium. This limits fall application to the northern portion of the United States. The concern with fall application is that losses of N will occur between application and crop uptake in the next growing season. This may lower crop yield and recovery of applied N. compared with spring applications. Recommendations for fall applications are to use an ammonium form of N. preferably anhydrous ammonia, and delay application until the soil temperature is below 50 degrees F.
Considerable year-to-year variation in the effectiveness of fall N application occurs, as shown in (Vis. 6).
These data illustrate that 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. In (Vis. 7), 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.
Preplant vs. Sidedress Applications
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.
Sidedress applications of N on irrigated sandy soils produce consistently greater yields than a preplant application, as shown in (Vis. 8). In areas where rainfall greatly exceeds evapotranspiration, the same results are expected. Sidedress applications on coarse-textured/low CEC soils are usually more effective in increasing corn yields than preplant treatments containing a nitrification inhibitor.
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.
Split or Multiple Applications
Application of N fertilizer in several increments during the growing season can be an effective method of reducing N losses on sandy soils with high potential for N loss through leaching. Irrigation systems equipped for simultaneous application are often used to apply N in multiple applications. The timing and distribution of N additions in a multiple application system are important. To match N uptake by corn, application of some N must occur by the sixth week after planting and most of the N requirement should be applied by the tenth week after planting. Research data suggest that a well timed sidedress application can be as effective as multiple applications in irrigated corn production. A combination of sidedress applications and N additions in irrigation water may be needed to maximize corn yields on some sandy soils. Preplant additions of one-third to two-thirds of the total N requirement, with the remainder applied later, are not as effective as sidedress applications on irrigated sandy soils.
On adequately drained medium- to fine-textured soils, the potential for N loss is low and the use of delayed or multiple N applications usually will not improve corn yields. Adjusting the sidedress fertilizer N rate using the pre-sidedress or late spring soil nitrate test is an advantage to a split application on these soils. This approach would permit adjusting for factors that affect N loss or gain and cannot be predicted.
| Visual title - Visual size | Visual title - Visual size |
|---|---|
| Yield of corn as affected by Nitrogen rate, time of N application - 17K | Effect of N rate, time of application, N source, and nitrificatio - 22K |
| Effect of N rate and time of application on corn yield for irriga - 13K |
