Statewide
Plant population in grain sorghum is a key to fitting your production potential to field conditions. But seeding rate does not equal plants per acre, and just because you set an air-vacuum planter to a target seed drop doesn’t ensure you are close to that number of seeds let alone plants.
Whether you have an existing crop in West Texas or have already harvested in South Texas (but your stubble is still standing), estimate actual plants per acre. Record this number in your field notes. Use the equation below and repeat it at least 3 times in a typical field area. Calculate a separate average for a thin area of the field, but watch it at harvest time to see if your yield is actually different (you may expect lower yield, but that is not always the case). Use all measurements in feet (including how wide the row is).
(43,560 sq. ft./acre) X (Plants in count area) = Plants per acre
(Length of count area) X (Row width) X (# of rows)
For example, if you measure two 30-inch rows 25 feet long and count 110 plants, then:
(43,560 sq. ft. per acre) X (110 plants) = 38,332 plants per acre
(25) X (2.5) X (2)
Round to the nearest 1,000, i.e., 38,000, then average this with at least 3 other points. You may have difficulty distinguishing tillers from the main stem, but count only individual plants (ignore small plants that will not contribute to grain yield). This method is easiest if counted 30 to 45 days after planting.
Some producers are familiar with counting plants in a fixed distance per single row, then multiplying by 1,000 to determine plants per acre. For a specific row spacing, use the length provided below (e.g., 1/1000th of an acre) then multiply by 1,000 to estimate plants per acre.
Row Spacing Length of row for plant count
20” 26’ 2”
30” 17’ 5”
36” 14’ 6”
38” 13’ 9”
40” 13’ 1”
