Billy E. Warrick, Extension Agronomist (Retired)
In times of crisis or disaster, farmers want to estimate potent ial yield of wheat well before harvest. Wheat yield is a function of three yield components: heads per square foot, seeds per head and seed size.
In Texas wheat fields, it is not uncommon to find head counts ranging from 5 to 100 per square foot at harvest time. Seed per head frequently varies from 15 to 60 per head, and seed size may vary from 12,000 to 18,000 per pound.
During the early vegetative growth stage, yield can only be estimated from viable tillers per square foot, with assumptions made about seed size and seeds per head. After the head is formed, better estimates can be made by plugging in estimates of seeds per head.
Seed size is determined after bloom, when little need to estimate yield exists. Seed size varies greatly with available moisture, plant disease and with variety.
Example models 1, 2 and 3 below estimate yields at 15, 20, and 40 seed per head. These examples give a constant seed size of 14,000 per head. Example 4 estimates yield at 20 seed per head with a seed size of 18,000 per pound.
Estimated Yield (bushels per acre)
( No. of heads per square foot X 43560 X [(No. of seed per head) / No. of seeds per lb.] ) / 60
or
No. of heads per square ft. X (No. of seed per head / No. of seeds per lb.) X 726
Example 1: assume 15 seeds per head and seed size of 14,000 seeds per lb (Table 1)
Yield = ? heads per square ft. X [ (15 / 14,000) X 726]
Yield = ? heads per square ft. X 0.78
Example 2: assume 20 seeds per head and 14,000 seeds per lb (Table 2)
Yield = ? heads per square ft X [ (20 / 14,000) X 726]
Yield = ? heads per square ft. X 1.04
Example 3: assume 40 seeds per head and 14,000 seeds per lb
Yield = ? heads per square ft X [ (40 / 14,000) X 726]
Yield = ? heads per square ft. X 2.08
Example 4: assume 20 seed/head and 18,000 seed/lb (Table 3)
Yield = ? heads per square ft X [ (20 / 18,000) X 726] Yield = ? heads per square ft. X 0.81
NOTE: Tillers to be counted poses a potential problem. In late planted wheat, count only tillers with three or more viable leaves as wheat breaks dormancy. At jointing, count only tillers with five leaves or more. Table 1, Table 2, and Table 3 give quick charts for estimating yield from viable tillers per one foot of drill row based upon four drill row intervals.
This is a HTML version of information developed initially by Travis D. Miller and Brent Bean. A word of appreciation is extended to them for their work.
