As I travel across the country, I frequently see big differences in the way farmers manage nitrogen (N)
applications. While some of the application strategies are specific to their region, rainfall or soils, the core components remain the same. N is still the most expensive input for a wheat crop. It’s almost always the most cost effective input, too, returning four to 10 times the cost.
Nitrogen application is a delicate balance, though. If you apply too much N, especially too early, then lodging and low yields will likely occur. If you apply too little total N, particularly not early enough, then yields will be limited with reduced tiller numbers, head numbers and head size.
To streamline N rates and timings, follow these suggestions:
- Begin with a sound understanding of residual N in the soil. For example, is the wheat following a legume, such as alfalfa, which leaves a lot of N in the soil for the following crop? Has the field had manure, such as chicken litter, or another source of residual N applied in some areas? In contrast, is the wheat following a good yielding corn or wheat crop, which soaked up most of the N from the previous season, leaving very little N for this year’s wheat crop?
Even on the same farm, N requirements vary based on soil type and rainfall—both influence losses and how much N will remain in the soil. A late fall or early spring soil test sampling 12" to 24" down is a great tool to help determine residual N levels. While the results can be a snapshot in time and specific to soils and rainfall, they are often helpful in refining spring N rates and timings.
- Determine the yield goal because it will dictate the total N rate. Be realistic but optimistic, especially if you have a good uniform stand. I often average the past five wheat crop yields and add 20% to use as a benchmark for N rates.
Many producers still apply all their N early and don’t apply additional N late in the season. In an average growing season, this might be fine, but when rainfall occurs early and N losses are higher, additional N might be required to bridge the gap between available N and what the crop needs for maximum yield potential.
- Time N just right. If you have a lot of N in the soil, for example, and the wheat follows corn, which had 200 lb. per acre of N applied and only made 75 bu. per acre because of a drought, then a considerable amount of residual N will remain in the soil (unless the wheat is grown on sandy soils in a high rainfall area). Assuming you’re not farming sandy soils with high residual soil N levels, I suggest reducing the total N rate—specifically the amount applied early in the season because excess early growth and lodging will likely occur if the crop is stimulated with early N.
By contrast, wheat following a 200 bu. per acre corn crop that had 180 lb. per acre of N applied shouldn’t have much N left in the soil. As a result, more total N will be required, specifically more N early in the season to boost tiller numbers, especially if the wheat was planted later or no-tilled into cornstalks (or both).
We almost always advocate splitting spring N, primarily because you will have a better understanding of how much total N the wheat crop needs later in the season, usually around the jointing stage. In addition, the early growing season can influence how much N is mineralized from organic matter or lost from the soil via leaching or denitrification.
Splitting N doesn’t cost—it pays by improving nitrogen efficiency, reducing potential for loss and almost
always helping to reduce lodging in most areas. Don’t forget that additional N can be added later in the season if yield potential is greater than what you fertilized for early in the season. We have seen yield responses to N applied as late as the flag leaf emergence stage (but only in a deficient crop) so it’s important to monitor crop health throughout the season and use tissue tests to help determine if additional N is required.
- Select N products that can be applied accurately, uniformly and in a form that’s available at the right time based on the demands of the crop. Too many producers concentrate on cost, rather than these logistic factors, which will make a bigger impact on crop yields.
For example, urea often costs slightly less than liquid nitrogen (UAN), but if the farmer only has a twin-disk spinning disk fertilizer spreader to apply it, he might be better off switching to liquid at the slightly higher price. This will assure the N is applied evenly and accurately using a sprayer.
A sprayer is able to apply liquid N accurately across the boom, plus it likely uses the same wheel tracks to apply a fungicide later in the season. Many farmers and dealers are now equipping sprayers with swath control and auto-steer, which further increases accuracy and brings overlaps on the ends down to almost nothing.
If you choose to apply dry fertilizer, make sure you use a well-maintained air truck because they are less sen-
sitive to any changes in fertilizer quality, wind and slopes. This will enable the applicator to spread dry fertilizer much more accurately.
- Consider some of the latest optical crop sensing technologies. I have worked with most of the commercially available systems for the past 15 years, and almost every replicated variable rate N trial I have conducted has resulted in an economic response compared to flat-rate applications.
N-rich strips are used in each field and variety to calibrate the systems. Once the systems are correctly calibrated, sensors mounted across the boom can adjust N rates up or down depending on the color and health of the wheat. We often see yield increases and lodging reductions when using variable-rate applications of N, and in most examples, we see reductions in total N rates.
Register Today to Attend Farm Journal Winter Events
Feb. 24, Manhattan, Kan.
High-yield wheat expert Phil Needham will highlight tips farmers can take straight to the field to increase wheat yields. Topics will range from fertilizer management and nitrogen use to new technologies and disease management techniques.
Wheat and Soybean College
March 3, Coldwater, Mich.
Join Farm Journal Associate Field Agronomist Missy Bauer and high-yield wheat expert Ronan Cummins for training on the fundamentals for high-yield wheat and soybeans. Learn about growth stages, fertilizer management, and disease, insect and growth regulators.