Judging by the questions raised at winter meetings and recent articles in farm publications, the interest in sidedressing N is increasing.

The renewed interest, no doubt, is spurred by the high prices for fertilizer N. Looking back, there was a time when sidedressing was a popular management practice. For various reasons, the popularity of sidedressing diminished. Since this application method is becoming more popular, now might be a good time to review what we’ve learned about using this management practice.

N APPLIED WHEN RATE OF N UPTAKE INCREASES.

Corn growth is chacaracterized by an increasing rate of N uptake between the knee-high and shoulder-high growth stages. This time period has sometimes been called the grand growth stage of corn. When N is sidedressed, availability of N during this stage of growth is at a peak. With the matching of time of application to maximum rate of growth and uptake, there should be maximum efficiency in N use thereby minimizing loss of N to the environment without negatively affecting yields.

THE IMPORTANCE OF SOIL TEXTURE.

In most of Minnesota, there is more than one opportunity for application of fertilizer N. However, soil texture considerations are important for timing decisions. For the fine-textured soils of west-central and southwestern MN, fall, spring preplant and sidedress application are all appropriate and the corn producer in the region can choose the time of application that best fits his farming enterprise. Results of research trials conducted over several years in this region show that sidedressing N does not produce a decrease in yield. In some years, when weather conditions conditions are conducive to N loss, there was an advantage to sidedressing N.

In southeastern Minnesota, fall-applied N, regardless of source, is not a Best Management Practice. The corn producer can choose between preplant and sidedress applications with both sources producing equal yields.

Considering soils with a loamy sand or sandy loam texture, sidedressing N is a very important management practice. This is especially true for irrigated production. In recent years, corn producers who farm these soils have seemed to switch from spring preplant to sidedress N applications. This is important for added yield and improved environmental quality. For non-irrigated sandy soils, the sidedress timing is strongly suggested. There are several reasons; but protection of water quality is one that stands out.

START EARLY.

The critics of sidedressing N point to the potential difficulty posed by frequent rains. The window of opportunity for sidedress N can be opened wider if there is an earlier start to sidedressing. There’s no need to delay. Sidedress applications can be started as soon as it is possible to “row the corn”. Since cultivation is used on very few acres, the conflict between this weed control measure and sidedressing is probably not a major consideration in today’s farming enterprises as was the situation several years ago.

SOURCE NOT A MAJOR CONSIDERATION.

You’ve probably heard the general statement that ” a pound of N is a pound of N, regardless of source if the source is applied to minimize loss”. This statement also applies directly to sidedress applications. If 28-0-0 or 46-0-0 is used, there is potential for N loss if applied to the soil surface without incorporation. The loss is attributed to the mechanism of volatilization. This is especially true for calcareous (high pH) soils. Injection or incorporation at the time of application or soon thereafter minimizes the potential for this type of loss. So, plan on some type of light incorporation if injection is not used at the time of application.

CAN RATES BE SHAVED?

This is a question that has been on the minds of many growers. This question has also been the focus of various research projects. Using several N rates and various timings, the results support the conclusion that rates cannot be reduced if sidedress applications are used. Again, the key is to apply the N source so that the potential for loss is minimized.

Those who reached the conclusion that lower N rates were possible if a sidedress application was used probably applied N in the fall or in the spring before planting in ways that did not prevent the potential for N loss. Keeping potential N loss to a minimum is a goal that should be used by all who apply fertilizer N.

A FUTURE FOR SIDEDRESSING?

Considering the emphasis on efficient use of fertilizer N in the years ahead, it seems that increased use of sidedress N is in the future. This practice is now a standard for most producers who grow corn on irrigated sandy soils. With recent advances in the technology to detect the N status of the corn crop, it’s relatively easy to picture a N management system in which some “base” rate of N would be applied either in the fall or before planting. The N status of the corn crop would be evaluated via sensing technology and the fertilizer N needed to achieve optimum yield would be applied as a sidedress application. Substituting topdress for sidedress, this system works well for winter wheat production. The concept appears to be one that will work with corn. However, considerable amount of field research must be completed before this concept can be refined to the point where it is practical and can be used on an extensive basis.

SOURCE: George Rehm