By Greg LaBarge, CCA, Ohio State University Extension agronomist
The USDA-NASS, Ohio Field Office estimates that Ohio farmers planted 700,000 winter wheat acres in fall 2021. The last time we were close to that many wheat acres was in 2013. We had excellent yields in 2021, with a historically high state average yield of 85 bushels per acre, 5 bushels higher than the previous record in 2016. Replicating our success in 2021 will depend on management and weather, especially temperatures and moisture at grain fill. Here are a few management steps for March.
Spring stand assessment
The best time to do stand assessments is Feekes 5 growth stage, where leaf sheaths are strongly erect (Early to Mid-April). A stand that looks thin in the spring does not always correspond to a lower grain yield. Rather than relying on a visual assessment, we suggest counting the number of wheat stems or using the mobile app Canopeo to estimate wheat grain yield.
Laura Lindsey, State Extension Specialist, Soybeans /Small Grains with funding from the Ohio Small Grains Marketing Program, has evaluated the relationship between wheat stems (main stem + tillers) and yield. The criteria used in making the counts were:
- Count the number of wheat stems which included both the main stem (main plant) and tillers.
- Stem counts were made in several areas of the field.
- Stem counts at Feekes 5 growth stage predicted wheat yield better than stem counts at Feekes 6 growth stage (first node visible).
If you do not want to spend an April afternoon counting tillers, Lindsey’s group also worked with a smartphone app called Canopeo to determine the fractional green canopy cover from an image. The Canopeo app is available for a variety of mobile platforms at http://canopeoapp.com. After accessing the app, hold your cell phone parallel to the ground to capture three rows of wheat in the image and take a picture. The app will convert the photo to black and white and quantify (as a percentage) the amount of green pixels in the image. Note if you have a weedy field, the weeds will also be quantified and overestimate the wheat canopy cover.
After counting the number of wheat stems or measuring canopy cover using the Canopeo app, use Table 1 to estimate wheat grain yield. For example, if you count an average of 51 stems from a one-foot length of row, the predicted grain yield would be 100 bushels per acre. Similarly, if the average canopy cover were 35%, the expected grain yield would be 100 bushels per acre.
Table 1. Estimated grain yield based on the number of stems or fractional green canopy cover (FGCC).
|Grain Yield (bu/acre)||Stem Count (number/foot of row)||Canopy Cover (%)|
This table was generated using data from two years and two locations (four different environments). During these two years, wheat grain yield was relatively high. Unfortunately, we do not have data for wheat grain yield <85 bushels per acre. Lindsey’s group continues this work and hopes to capture a broader range of yields to expand this table. For more information on stand assessment, see https://go.osu.edu/stand.
It is essential to apply herbicides at the correct stage of small grains growth to avoid crop injury. Making weed control decisions before or during Feekes 5.0 provides the greatest range of herbicide options. As wheat advances past jointing (Feekes 6.0) and approaches the boot stage, herbicide choices become limited. Most herbicides can be applied in UAN when the small grains are topdressed. Applying herbicide in UAN can increase crop injury somewhat, and some labels recommend adjusting surfactant rates to minimize damage.
Nitrogen applied at Feekes 5.0 can affect the number of seeds per head and seed size, but not the number of heads per square foot or the number of spikelets per head. Therefore, this is an ideal growth stage for the spring topdress N application.
We use yield potential for wheat N recommendation. Table 2 provides N rate recommendations. Recommendations are based on the following equation: N Rate (lb N/acre) = (1.33 x Yield
Potential) – 13. These recommendations are for mineral soils with adequate drainage and 1 to 5 percent organic matter.
Table 2. Nitrogen rate for wheat by yield potential. (Source: Tri-State Fertilizer Recommendations for Corn, Soybean, Wheat, and Alfalfa)
|Yield potential(bu/A)||Total N rate (lbs/A)|
We do not give any credit for the previous soybean or cover crop. Mineralization of organic N is soil temperature-driven. Thus, cool spring conditions slow down the process. The recommendation suggests that you subtract any fall-applied N from the total N recommendation to determine the spring topdress rate applied.
Split N application makes it possible to evaluate yield potential and adjust the total N rate. Apply a partial rate of N after green-up and then use the wheat assessment to determine yield potential can improve N use efficiency. A caution with wheat and nitrogen is too much nitrogen will result in lodging, making harvest difficult.
Using manure as a nitrogen source is a great opportunity considering current nitrogen prices and concerns about sourcing fertilizers. Lodging from excess N is a genuine concern when using manure in wheat. This past week, I talked with a livestock producer who used liquid manure on wheat in 2021. He had a 103 bushel per acre crop, but lodging was an issue. One day it was a deep green color standing upright, the next day, it was laying flat. He was thankful a combine with a draper was available. The manure test is the key to knowing the correct amount of manure to meet the N need. Most manure tests show total nitrogen, ammonia nitrogen, and organic nitrogen amounts. The ammonia nitrogen portion is readily available for plant growth. Use the manure ammonium content with Table 2 to determine the amount of manure to apply. Here is an example of manure rate using nursery manure with 14 pounds ammonium per 1,000 gallons. For a 90-bushel wheat crop, the rate from Table 2 is 110 pounds of N. Take 110 pound need divided by 14 would equal 7,857 gallons. Remember to subtract off any starter N before determining the final application rate.
We have a great factsheet that shows how to determine wheat growth stages and highlights management decisions for each growth stage https://go.osu.edu/wheatgrowth. In addition, our CORN newsletter https://agcrops.osu.edu/ goes back to a weekly edition on April 4. It is an excellent source for wheat, corn, soybean, and forage management information throughout the year.