By Carrie Knott, Extension Agronomist-Princeton, University of Kentucky
Despite the blanket of snow many of us woke up to this morning it is the time of year to be considering nitrogen applications and other input decisions for this year’s wheat crop. We had a relatively mild fall for much of the state, which resulted in really nice stands of wheat. When I say “nice stands” I mean they have produced many tillers and filled out well.
The wheat crop will likely be breaking dormancy and begin “green-up” (actively growing) very soon. Once green-up occurs (Feekes growth stage 3; Figure 1) you should immediately start your tiller counts so that you can make some key agronomic decisions.
Figure 1. Feekes growth stage system for wheat.
To determine tiller counts, count the number of wheat stems and tillers that have three or more leaves in a specified length of row (ID-125 page 19). Most commonly only a one foot length of row is counted to reduce time at one particular area of the field and allow time to take multiple tiller counts in the field. You want to take tiller counts at multiple areas of the field that are similar to the stands of the majority of the field. That is, avoid areas of the field that either have excessively high plant populations (possibly caused by planter overlap) or have very low plant populations (due to waterlogging or a variety of other effects).
The University of Kentucky considers an “adequate stand” at Feekes 3-green-up- to be more than 70 tillers per square foot (ID-125 page 19). If tiller counts for a particular field are more than 70 tillers per square foot (Figure 2) at green-up, consider a single nitrogen application this year.
Figure 2. Number of tillers per square foot based upon number of tillers counted per linear foot of row.
In general a yield increase of 3-5 bushels per acre is achieved with split nitrogen applications in Kentucky. Our traditional split is one third the nitrogen rate applied at green-up (Feekes 3) and two-thirds applied at Feekes 5 (Figure 1). This is strategy will attain the highest yield potential; however this year to maximize profitability it may literally pay you to make a single nitrogen application between Feekes 4 and 5. Not only will you be able to save the cost of one trip across the field, but you will also be able to reduce your total nitrogen applied by 5-10 lbs N/A.
For example, you have a no-till field planted on 7.5-inch row spacing and you count tillers at 10 representative sites in the field. The average tiller count for the entire field is 96 tillers per square foot (about 60 counted tillers per linear foot of row; ID-125 page 19). To minimize input costs and still produce good wheat yields you could apply 100 to 105 lbs N/A in a single application between Feekes 4 and 5 (Figure 1 and ID-125 page 7 & 8), instead of a total of 110 lbs N/A with a split nitrogen application.
What if you have a field where half of the field has adequate stands, more than 70 tillers per square foot, while the other half of the field has less than 70 tillers per square foot. In this case I would recommend a split nitrogen application. Although on average you will only get a 3-5 bushel per acre yield gain, when inadequate stands exist in the spring the yield gained with a split application is much higher than the 3-5 bushels per acre. The split application in this case will stimulate early spring growth and tillering, which should contribute to yield at the end of the season.
Other considerations for the 2016 wheat growing season are to make sure you provide adequate fertility to attain good yields (AGR-1) and protect your grain from vomitoxin accumulation with and early flowering fungicide application. The proper timing for Fusarium head blight (casued by Fusarium graminearum) control is when 50% of the field has reached Feekes 10.5.1 (beginning flowering; Figure 3).
Figure 3. Image depicting beginning flowering in wheat (Feekes 10.5.1).
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