In order to maximize grain yield, we need between 500 and 900 heads/sq. yd. at harvest. Wheat sown at 1 bu/ac will generally result in about 175 seeds/sq. yd. meaning that we will need at least three tillers per seed that go on to make a wheat head. Not just any tiller will suffice. If a tiller does not have three large, unfolded leaves by jointing, there is a good shot that it will not make a head.
One of my primary concerns right now is tillering in many Oklahoma wheat fields will be insufficient to reach the critical 500 heads/sq. yd. number. Even though most of our wheat was sown in October, a lot of it will have a November or December (if we are lucky) germination date. A K-State study from 1995 showed that wheat emerging on November 30th produced an average of only 1.8 viable heads per plant at harvest. If we had known that our emergence date would be in November or December, we would have compensated by doubling or tripling our seeding rate.
September-sown wheat that got a good start but is now backpedaling due to a lack of moisture is a different issue. In the same study mentioned above, wheat emerging October 12 produced 1,850 tillers per plant on average. Only 476 (26%) of these tillers made it to harvest, so it is normal for early-sown wheat to slough off several tillers. This has an energy cost to the plant and is one reason early-sown wheat generally yields less than October sown wheat. We have enough tillers present in our early-sown wheat but are losing them quickly. Rain is needed quickly to stop the losses.
Agronomists are second only to lawyers in including disclaimers and qualifying statements, and there is a lot of wiggle room in the numbers I have provided. A variety that typically produces larger heads (e.g. Billings) can be on the lower end of the 500 – 900 head range and a variety with smaller heads (e.g. Duster) will need to be on the upper end.With a warm winter and rainfall, we could still hit these targets. However, to borrow some terminology from Vegas, I think there are fairly low odds that our wheat will cover the spread when it comes to tillering this year.
It was too nice of a day to stay in the office yesterday, so I checked on our wheat variety plots. I started at McLoud, moved west to Kingfisher, and ended up at Marshall. As indicated by the pictures and captions below, neither the wheat nor my mood improved as I traveled west. I am sure if I had traveled farther west, this would have gotten worse. The bottom line is that we are in desperate need of moisture in Oklahoma. Early-sown wheat is backpedaling quickly and cannot hold on too much longer. Much of the later sown wheat has yet to emerge. We are certainly not on our way to a record year, but everything could still turn out okay……..if it rains.