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Strategies For N On Wheat This Spring
DR. WILLIAM J. WIEBOLD
COLUMBIA, MO.
It was a difficult fall in Missouri and much of the Midwest. Crops came out late, crops came out wet, fields were rutted, wheat got planted late or not at all, and once the wheat was up it found itself in a hostile (cold & wet) environment.
The wheat that went in is mostly a lot smaller than is normal for this time of year. Late-planted wheat has already lost some of its inherent yield potential. The number of fall tillers is reduced by late planting, root development is not as extensive, and sugar reserves are below what you’d want.
I suggest higher seeding rates when planting late in order to make up for reduced tiller development. But that water is already over the dam.
In most years, we’d be seeing greenup in wheat in Missouri already by now (February 25), but with a lot of cold, snow, and wet, that is not the case.
There may be fields where ice damage or winter-kill or drowning has caused stand loss and a decision will have to be made about whether to keep them.
For fields that are kept, early spring nitrogen will spur formation of additional tillers. My belief is that spring tillers are not as valuable as tillers formed in the fall, but they can still make substantial heads. I would think that most Missouri wheat fields would benefit from some N as early as possible.
When I was a graduate student, I did an experiment to see whether later winter or early spring N could overcome the negative effects of planting three weeks late. The answer was no. The early N helped the late-planted wheat, but it never caught the wheat that was planted on time.
I also counted tillers just before jointing in plots that got different N rates at greenup time. In both fields where I did this, wheat with no N at greenup had fewer tillers than wheat with 30 N at greenup. Wheat with 30 N at greenup had fewer tillers than wheat with 60 N at greenup, but 60 and 90 lb N greenup N rates had the same number of tillers.
Some producers moved aggressively to get early-spring N on their wheat. This sometimes meant applying when the ground was frozen. This will probably work out fine if there was a gradual thaw and no rain. I heard of one case this year where there was 0.3" of rain after applying N on frozen ground. I would say that N could have been lost as the rain ran off the field, and have seen fields in the past where this definitely happened. Keeping an eye on the crop will show whether the N is still there or not. Sometimes even when ground is “frozen”, water can still infiltrate and runoff is low.
It would be reasonable to put out the full spring N application when conditions allow. I have rarely seen a yield reward for splitting spring N applications in my research. But if there was a year to consider splitting, this might be that year.
It's likely that the period from greenup to jointing will be shorter than usual this year. That means less time for tiller initiation. If the first N application is delayed for several more weeks, it may be too late to have much effect on tiller population. So if there was a year to consider using a plane to get N on wheat, this might also be that year. A low rate (70 to 100 lb urea with an inhibitor containing NBPT) with a plane, followed by the main application any time up until jointing, could turn out to be a successful strategy.
Whether applied with a ground rig or from the air, all urea applications to wheat should be treated with (or be co-granulated with) a volatilization inhibitor containing NBPT. ∆
DR. WILLIAM J. WIEBOLD: Professor Plant Sciences, University of Missouri
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