Statewide
For any grain sorghum crop, the yield you realize across a field is a function of several factors. Of course, weather—especially rainfall—has a large impact. Your fertility program is an important key, especially for nitrogen. Whether economic thresholds of insects develop and how they may diminish your yield potential will be determined in how you control those pests.
But when a field of grain sorghum establishes, develops, and ultimately produces grain, where does the actual yield come from? Research demonstrates—as an average between irrigated, rainfed, and semi-arid dryland production—that the following yield factors in the sorghum plant itself generally establishes the contribution to grain sorghum yield:
· Seeds per head 63% of yield (higher in dryland)
· Heads per acre 30% of yield (higher for irrigated)
· Seed size/test weight 7% of yield
Seeds per head makes a proportionally higher contribution in limited rainfall dryland, up to 70% or more.
What does this mean for a producer? Is this something your management can influence? Though irrigation, if you have it, alters your production options considerably. Naturally you use plant population to increase your yield potential. This data suggests—strongly—that seeds per head is a greater contributor to yield than heads per acre. You can indeed have too many heads per acre (whether from planting too much seed or from significant tillering, which may not be in your best interest the drier it gets), and the end result is higher heads per acre can actually limit your potential grain yield.
The bottom line, especially for dryland and limited-rainfall dryland, is that grain sorghum’s ability to compensate for yield is more in the head (seed number) than in the number of heads per field. Knowing this enables producer to manage (reduce) risk by using modest and even low seeding rates in rainfed and especially in limited rainfall dryland production. These reduced seeding rates actually favor the factor that research demonstrates has a greater impact on grain yield: seeds per head.
