First determine the number of plants per square foot as follows. Take a yardstick 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 (%)|
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. 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. Although there seems to be some debate about whether early nitrogen topdressing stimulates more tillers, 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.
Topdressing very early before green-up puts nitrogen out on the field before the crop can use it. With cold temperatures there probably won't be much loss from volatilization of urea before the next rain. Ammonium forms of N are stable and won't be lost from conversion to leachable nitrate under cold soil conditions. The main risk of loss is from nitrate forms of fertilizer applied (leaching) or under conditions where the fertilizer (in any form) is washed off the surface before it gets into the soil.
We have a video on assessing wheat stands in the Grain Crops section of this site.