By John Rowehl
Check on the effects of late planting and/or winter weather
Some wheat fields get planted late every year and adequate plant population and fall tillering may not have been achieved. As winter grains are greening up growers are able to see the actual amount of survival that they got out of these fields that are in question. There are some guidelines for stand assessment that growers can use to determine between keeping the field as it is or if replanting with a spring crop would be better. Because small grains can compensate well for reduced stands, some reduction in plant population is acceptable.
Figure 1. Checking wheat plant populations
First determine the number of plants per square foot as follows. Take a yardstick or any three-foot long stick and lay it along a row. Count the number of plants in the three-foot length. Repeat this at several random locations that represent the field condition and determine the average. Multiply this number by 4 and then divide by the number that is your row width. For example, 40 plants (per 3 ft), X 4 / 7 = 23 plants per square foot. Twenty to thirty (20-30) plants per square foot is considered adequate for maximum yield.
| Plants/sq ft | Yield Potential (%) |
|---|
| 30-35 | 100 |
| 22-28 | 100 |
| 18-21 | 90-95 |
| 15-18 | 75-80 |
| 12-14 | 60-70 |
If the number of plants per square foot is less than 12-14, consider replanting to another crop.
Determining the number of tillers can also be helpful. Tillers are secondary stems that branch out from the base of the main stem. Knowing the number of tillers can provide a guideline for timing nitrogen application as described below. Count the number of tillers (including main stems) from three feet of row (also at several random locations) and do the same calculation.
Less than 60-70 tillers per square foot is considered low. In a case like this, our recommendation is that some of or all of the spring nitrogen be applied at early green-up to try to get more tillers formed. If there are 70-90 tillers per sq. ft., it is not as critical to get nitrogen on and it can be delayed until just before the stems begin to elongate (growth stage 5). With even higher tiller counts, also delay top-dress until stage 5, as the nitrogen demand of the plant begins then. However, topdressing after stem elongation has advanced much beyond this can reduce yield.