Evaluating winter wheat stands
March 21, 2014
Warm days and nights have raised soil temperatures into the mid and upper 30's in much of South Dakota, enough to take the frost out of the top several inches and begin to bring winter wheat out of dormancy. Cool days and nights in the forecast will slow the process, but we're at the point on the calendar where winter wheat fields will soon begin to look green if they are alive. Articles earlier this winter have suggested that much of the winter wheat crop is expected to have survived the winter relatively well. Those articles were based on monitoring soil temperatures at automatic weather stations, precipitation, soil moisture and limited actual field inspections. Undoubtedly there will be locations in the state that are dry, wind erosion occurred, or for other reasons, some of the winter wheat was damaged by winter injury.
As the winter wheat begins to grow, producers will be able to accurately assess their stands, and degree of winterkill that occurred, if any. This will help make decisions on whether to keep the stand or destroy it to go to another crop, and take appropriate management strategies.
Evaluating a winter wheat stand early consists of two aspects, plants per square foot, and how uniform the stand is. Yield is directly affected by the number of plants per square foot in the field. Optimum plant stands for winter wheat are said to be 18 or more plants per square foot. If uniformly distributed, 5-6 plants per square foot is considered to be the minimum. Winter wheat has the ability to compensate for lower plant densities by tillering, but there is a limit to that ability, and the plants must be uniformly distributed to take full advantage.
To evaluate a winter wheat field early in the season, you have to make several assumptions. If we assume 1 million kernels per bushel, 25 kernels per head, and 5 tillers per plant, 8 plants per square foot would produce 44 Bu/Acre. Main stems often produce more than 25 kernels, but secondary tillers will bring the average down. High plant populations typically produce fewer than 4 tillers, whereas low plant densities will likely result in considerably more. Each producer will need to decide what yield potential is adequate for their operation.
The general recommendation for nitrogen fertilization is to have all or most of the nitrogen applied before jointing. Early jointing is the stage at which head size is being determined, and providing optimum nutrients will help take advantage of that. There is some thought that nitrogen applied early will stimulate tillering, although possibly to a limited extent. Application should be delayed until the soil is no longer frozen but dry enough to support traffic. If the spring is wet, the window of opportunity may be narrow enough that getting it on early will help insure that the nitrogen is available before jointing occurs.
Weed control becomes more important with a thin stand of wheat. If the crop is planted into wheat stubble, adding a half rate of fungicide with the herbicide may help maintain secondary tillers and subsequent yield potential.
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