Across the three counties in the Mid-Coast IPM Program, grain sorghum planting rates range from 40,000 to 120,000 seed per acre. The ideal planting rate varies due to soils, rainfall, and row spacing. A good starting place for planting sorghum is 65,000 seed per acre.
Sandy soils and lower rainfall averages usually need lower planting rates and heavier, clay soils and higher rainfall typically have higher seeding rates to obtain maximum yields.
Field research has been conducted in fields in Calhoun, Refugio and Victoria Counties revealing different results. In Port Lavaca, a trial was conducted in 2013 on 38″ rows. In this trial, planting rates of 71,000, 81,000 and 93,000 seed per acre were compared. No differences were found between the three seeding rates with grain yields averaging 6167 lbs/A (Table 1).
Similar trials were conducted in Refugio County near Bonnieview in 2013 and 2014 on 20″ rows. The planting rates compares were 35,000, 45,000, 55,000, 65,000, and 75,000 seed per acre. In these trials, yield differences were found in 2014 but not in 2013.
In 2013, the Bonnieview test showed no differences with sorghum yield averaging 4173 lbs/A (Table 2). The yield of the 2014 trial showed higher yields as the number of seed per acre was reduced (Table 3). Grain yield averaged 3476 lbs/A in 2014.
The Victoria County trial (2014) was a plant population trial instead of a seeding rate trial. Plant populations of 2, 3, 4, 5, and 6 plants per foot were compared by thinning the population after emergence. The sorghum was planted on 38″ rows. Yields averaged 4784 lbs/A.
The planting rates of 4, 5 and 6 plants per foot had similar yields (Table 4). Grain yield was reduced by plant populations less than 4 plants per foot. Four plants per foot on 38″ rows is 55,020 plants per acre.
These results show the ideal seeding rate for 20″ sorghum in the Bonnieview area is around 45,000 seed per acre because higher seeding rates resulted in lower yields in 2014. I do not think these results will be the same in the Austwell-Tivoli area of Refugio County.
Calhoun County sorghum planted higher than 71,000 seed per acre did not increase yield. Lower seeding rates may be better but were not evaluated in this trial.
The Victoria trial showed plant populations below 4 plants per food reduced yield. Based on these results, assuming 90% germination, sorghum should be planted at or above 60,000 seed per acre.
If I was planting sorghum from Victoria to Port Lavaca to Austwell, I would plant 65,000 to 75,000 seed per acre. In the Bonnieview area, I would plant 45,000 to 55,000 seed per acre.
More work needs to be done to refine the ideal seeding rates in the Mid-Coast of Texas including planting rates on narrow rows or drilled sorghum. These trials are fairly simple to conduct on farms with newer planters that have the ability to change seeding rates from the tractor cab. Yield can be measured with either yield monitors in the combine or with my weigh trailer.
Sorghum growers who want to look at seeding rates on their farm can contact me (Stephen Biles) at 361-920-1138 or email@example.com.