Recent rains have helped green up much of the drought-stressed Texas Panhandle wheat, said Dr. Brent Bean, Texas Cooperative Extension agronomist at Amarillo.

Now, back in the sunshine, area farmers are wondering about yield.

"If good moisture continues, wheat here may well make a comeback," said Bean. "Yield, however, is dependent on crop conditions before the rains."

What's in store weather-wise during March and April will make a huge difference, Bean said. Good yield depends upon many factors including the number of heads, seed per head and weight of each seed. Seeding rates and tillering are equally as important. Healthy plants also must have three to five tillers.

The key ingredient? Moisture, of course, Bean said. Germination and growth through harvest are tied to water in the soil profile combined with naturally occurring moisture for dryland crops or applied irrigation, where crop yields are highest.

Tillers, usually two or three primary ones form in the fall, followed by secondary shoots in late winter and early spring. Every tiller helps boost yield. This growth also impacts the number of seeds per head, another important contributor to yield.

This is especially true during the two weeks just before jointing, a time when wheat plant stems are formed from growth nodes. Bean advises farmers to check their stands during and after flowering.

When plants change from a vegetative to reproductive state, the potential for seed production is set. In the High Plains, the big switch takes place from March 4-24. Moisture stimulates more seed per head, but only in later growth stages.

The seed weight will be determined during grain fill. Wet, moderate temperatures are key promoters of weight gain. For any field with a reasonably good start, High Plains wheat still has excellent potential, even if some leaves were burned by the January cold. This can be true even when some primary tillers abort due to months of drought, Bean said. Late winter and spring tillers can make up for some of this loss.

"All we need for good spring tiller production is a cool, wet March," Bean explained. The potential for high numbers of seed per head also increases. Overall, these fields should have a reasonable chance to make a good yield, if good conditions hold.

Farmers may see fields with thin or spotty growth. Only four weeks ago, such crops were almost dead. This wheat could still produce, but a wet, cool March will be essential for tillering. If adequate tillering doesn't occur, the seed per head and weight still have some rebound potential. Bean said late forming ones cannot fully compensate, and farmers should expect some yield decline.

"Wheat is extremely resilient. Fields that looked like they might not make it back in January show potential for an average yield," said Dr. Jackie Rudd, wheat breeder with Texas Agricultural Experiment Station at Amarillo and Vernon.

But where plants have recently emerged, a "normal" yield is most unlikely, even under the best conditions, the agronomist said.

Don't count that field completely out, Bean said. A significant yield may be there. The caveat being a lack of vernalization, or the "chilling" of winter wheat seed required by the plant in order to produce a head.

"This natural protection mechanism keeps the plant's growing point below ground and insulated from winter freezing," Bean said.

With sufficient chilling and warming temperatures, the plant will enter its reproductive phase and jointing will follow. Day length also plays a role. The process ramps up as soon as the seed takes in water, but the plant doesn't need to emerge for vernalization to begin.

The best temperature range, Bean said is between 33 F and 50 F, but the amount of chilling required depends on the wheat variety. Some types need only a few days, while others may take as much as six weeks to vernalize.
Varieties having this short chilling time frame include TAM 101 and TAM 202. Jagger may have it as well. Bean's best guess? Any variety planted before Jan. 1 has had plenty of opportunity to chill out, even if recently sprouted.
"Clearly the yield potential for newly-emerged wheat has been significantly been reduced. But even the best of spring conditions will mean seed numbers per head and weights cannot make up for less-than-adequate tillering," Bean said.

Bean's rule of thumb for estimating yield potential: Count the number of plants, or better yet, the number of tillers per square foot.

"The closer to actual harvest, the more accurate the estimate," Bean said. Two publications will help farmers wanting to estimate yield. Each method requires that certain assumptions, or guesses, about seed number and seed weight. One guide is from Texas and the other from Oklahoma, and are available online: http://soilcrop.tamu.edu/publications/pubs/scs1999-21.pdf and http://www.agr.okstate.edu/plantsoilsci/extension/publications/wheat/pt-01-10/pt2001-10.htm

Research from Kansas and elsewhere suggests that yield can drop by as much as 20 percent for every month planting is delayed past an optimum date. On average, yield was lowered 50 percent with March emergence, when compared to fall wheat outings. Actual losses depend on the weather from now through grain fill.

"This recent moisture at least has given us a fighting chance," Bean said. For fields having a decent potential now, farmers should consider weed control and possibly a nitrogen application, which needs to be completed before jointing to do much good.

Writer: Pam Dillard