Assessing potential damage, estimating wheat yields
Table 1 is easy to use; however, it relies on several assumptions required to make a yield estimate in the fall or early spring prior to extensive tillering or stem elongation. These assumptions include:
- that the wheat plants, on average, develop about five heads;
- that each head, on average, develops about 22 kernels; and
- that there is an average of 16,000 kernels per pound.
To use Table 1, count the number of plants per foot of row. It is best to use at least five feet of row in at least five sites within the field and calculate the average number of plants per foot of row. If the stands are uneven, for example the stand is better or worse in the wheel tracks, make sure your percentage of samples in these areas accurately represents the proportion of these areas in the whole field. Locate the column in the table that corresponds to your average number of plants per foot of row and then move down that column until it intersects with the row corresponding to your row spacing. This is your estimated yield.
click image to zoom Late-planted wheat and wheat seeds that do not germinate until later because of dry conditions will tiller less and have fewer heads. Table 2 has the results of winter wheat planted September 28 to November 13 with October 11 the best planting date at Hutchinson, Kansas. Winter wheat planted a month later yielded 48% less. The general conclusion is to expect winter wheat that emerges after January 1 to have a yield reduction of at least 50% compared to the normal yield.
Table 3 was developed using data collected from 1994 to 1998 with the Nebraska Wheat Quality Tour. These tours were conducted near May 1, prior to head emergence in most of the state. Factors such as heavy weed, disease, or insect infestations or inadequate soil moisture at the time of the tour may suggest fewer final heads and a lower yield potential than indicated in the table. In addition, the table becomes unreliable in situations of extremely low or extremely high tiller counts, or in years when crop development as of May 1 is well ahead of or behind normal. For later season yield estimates, yield predictions can be made by substituting the actual number of heads per foot for tillers per foot.
click image to zoom To use Table 3, count the number of tillers per foot of row. Again, it is best to use at least five feet of row in at least five sites within the field and calculate the average number of plants per foot of row. Be sure sample sites are representative of the field. Locate the column in the table that corresponds to your average number of tillers per foot of row and then move down that column until it intersects with the row corresponding to your row spacing. This is the estimated yield. Although these multipliers may appear to be in error—everyone knows that wheat fields in the semi-arid Panhandle usually yield less than fields to the east—on a per head basis the multiplier is correct. Wheat fields in the sub-humid portions of the state produce more heads per acre, but typically fewer kernels per head than in the Panhandle.
For example, if your winter wheat field is in southwest Nebraska and you have an average of 30 tillers per foot of row, and your row spacing is 10 inches, multiply the table results of 40 bushels per acre by 0.9 to get a yield estimate of 36 bushels per acre.