Small Grain Yield Estimate

Wheat, barley and oats use the same three-component logic as corn but state the third term honestly, as a weight rather than as a count per bushel. Heads per square metre, grains per head, and the thousand-kernel weight of the variety, divided by 1000 because the weight is quoted per thousand grains. A good crop of 450 heads/m² carrying 32 grains at a 42 g TKW gives $450 \times 32 \times 42/1000 = 605$ g/m², which is 6.05 t/ha.

Thousand-kernel weight is a variety characteristic with a modest environmental range, which is exactly what makes the method work. Wheat typically runs 30–45 g, barley 35–50 g, oats 25–40 g, and a seed lot's actual figure is printed on the certificate. Because it is stable, most of the year-to-year variation in yield lives in the first two terms — the head count set by seeding rate, tillering and winter survival, and the grains per head set by conditions during the few weeks around flowering.

The counting error to watch is the quadrat. Use a fixed frame or a length of row against a known row spacing, count only FERTILE heads, and take enough samples that the field's variation shows up rather than one lucky patch. Counting heads in a row and forgetting to divide by the row spacing is a routine mistake and produces an answer several times too large — which is at least an obvious kind of wrong. Rounding the TKW from grams per thousand kernels to grams per hundred, or to a per-kernel weight, is the dangerous kind, because the answer stays plausible while being out by a factor of ten.

The same three numbers pay for themselves twice more. Read backwards, the equation turns a target yield into a head count and then, through an expected tillering rate, into a seeding rate — which is how variety-specific seeding recommendations are actually built. And TKW is the number that converts a seeding rate stated in seeds per square metre into the kilograms per hectare that a drill is set by, which is why it appears on every seed certificate in the first place.