How Perfect Do Wheat Stands Need To Be?

By Jochum Wiersma,
U of M Small Grains Specialist
wiers002@umn.edu

Perhaps you have heard me talk or write about the need to calculate seeding rate appropriately for each seed lot, to calibrate your drill carefully, and to check depth control and planter speed, all in pursuit of the perfect stand.  But how perfect do wheat stands need to be? 

Some preliminary research results with soft red winter (SRW) wheat in Kentucky showed that stands with less than 25 plants/sq ft yielded similarly to higher seeding rates.  The results indicated that, in Kentucky at least, stands do not have to be near perfect for high yields. Skips in the stand that comprised as much as 10% of the area were still yielding as well as on stands with no skips.  As the authors concluded, this demonstrated the remarkable ability of the wheat plant to compensate for lower stands with increased tillering.

I have to agree with the authors in that wheat (as well as other cereals) have a remarkable ability to compensate for errors and make up some, if not all, of the potential yield losses from a reduced stand. There are, however, words of caution.

1) The results do not imply that a reduced stand or sloppy planting may be an acceptable practice. Yes, wheat can compensate, but that doesn’t imply a license to do so.

2) The research was conducted with SRW in Kentucky. There are some considerable differences with hard red spring wheat and the growing conditions in the Northern Plains. For instance, SRW has a winter growth habit, and a lot more time to tiller when compared to HRSW.  SRW will already grow in early spring when daytime highs are not yet exceeding 75º F, and are near optimum for growth and development of wheat.  In comparison, HRSW production regions are typically much more arid and temperature extremes are larger. Our growing season progresses much faster than Kentucky’s winter wheat growing season.  Within weeks after planting, temperatures can soar well above the optimum of 75º. This forces the plant to develop quicker, and thus there is less time for tillering and the ability to compensate for less than optimum stands.

3) A lower than optimum or near optimum stand will result in a crop that has several different growth stages in the field.  Each tiller develops sequentially, and thus relying heavily on tillering will result in a wider range of growth stages.  This makes timing of your inputs like herbicides and fungicides, as well as uniform ripening at harvest, much more cumbersome.

Still, if stands are not optimum, wheat can partially compensate.  However, when do you decide to replant a stand? Assume you wanted a stand of 1.3 million plants per acre. That requires at least 30 plants per square foot.  Consider that replanting costs must be recovered from a later maturing crop that has a lower yield potential than the original crop. Plus, replanting uses extra moisture as a function of soil disturbance.

Use the following guidelines to determine whether replanting is worthwhile:

1) If reduced stand is uniform (no big skips or holes) keep stands at 15 plants per square foot.

2) If skips are large (3 to 6 ft), or holes are 4 to 6 feet in diameter and stand is 18 plants per square foot or less, then replant if moisture is adequate.

3) After June 1 in northern Minnesota, and May 15 in southern Minnesota, a replant decision should be to a crop other than wheat or barley since yields are reduced about 50% when planting after these dates compared to normal planting dates.

Thus, stands as low as 15 plants/sq ft, if uniform, should probably be left alone, because the chances for you to improve the yield potential by reseeding are probably not in your favor.  In conclusion, strive for an optimum stand, and know that a less than optimum stand of wheat doesn’t necessarily spell disaster, because of the crop’s remarkable ability to compensate with tillering.