Tip Provided by: Ronnie Schnell, Ph.D.
Cropping Systems Specialist
Texas A&M AgriLife Extension, College Station
A wide range in seeding rates and subsequent plant populations are used across Texas for grain sorghum production. Seeding rates used by growers range from <20,000 seeds/acre under rainfed conditions in the Texas High Plains, especially when at-plant deep sub-soil moisture is poor, to >90,000 seeds/acre under high rainfall/irrigated conditions downstate. Texas A&M AgriLife Extension recommendations for grain sorghum seeding rates are based on rates needed to obtain uniform and sufficient plant populations to optimize yield. Moisture (including stored soil moisture, projected rainfall and irrigation) is often the factor that ultimately determines the appropriate seeding rate.
Seeding rate has been discussed by Texas A&M AgriLife Extension in previous “Sorghum Tips”, which can be found by clicking on the titles of the tips below.
- Irrigated Seeding Rate Suggestions – May 15, 2012 (High Plains)
- Dryland Seeding Rate Suggestions – June 1s, 2012 (High Plains)
- Narrow-Row Grain Sorghum—Increase the Seeding Rate?: Probably Not – Feb. 6, 2013 (Statewide)
Additional grain sorghum seeding rate information prepared by AgriLife Extension is also found in the grain sorghum pocket production guides (three regional editions for Texas) at http://sorghumcheckoff.com/for-farmer/production-tools/.
Central & North Central Texas Seeding Rate Work, 2014
During 2014, a study supported by the Texas Sorghum Producers was initiated in central and north Texas to evaluate grain sorghum yield in response to a wide range of plant populations and environmental conditions. Field-scale replicated strips were used at five locations with seeding rates that ranged from 30,000 to over 90,000 seeds/acre. All locations started with sufficient soil moisture to depths of at least four feet deep. In-season rainfall ranged from 1.5 inches below normal to about 2.5 inches above normal. Yields by location ranged from about 5,500 to 8,000 lbs per acre. Little if any difference in grain yield was observed for the different seeding rates at most locations.
This trial work demonstrates that lower plant populations (<65,000 plants/acre) were not as sensitive to below or above normal amounts of precipitation compared to high populations (>85,000 plants/acre). In other words, lower plant populations maintained yield under less favorable moisture conditions where yields declined slightly for excessive populations. Often, lower yields for high plant populations are due to secondary issues, such as stalk rot. For central Texas, seeding rates between 65,000 and 80,000 seeds per acre (with about 90% stand) will provide good yield potential while reducing risks associated with higher seeding rates. In drier years, the lower end would likely be appropriate.
Central & North Central Texas — AND Statewide
The above “flat” results of sorghum grain yield in response to increasing seeding rates are not surprising considering sorghum’s ability to compensate for yield across a wide range of plant populations. This is accomplished through increased tillering and larger head size at lower plant populations. This provides a great advantage for low plant populations. Though not all hybrids respond to low plant populations the same way, reduced seed drop and subsequent plant populations allow the plants to adjust (increase tillering and head size) when conditions are favorable.