It’s August and that is when soybeans make yield. Soybeans are at late R4 (ending pod set) or R5 (beginning seed set). Everyone knows that August rains are critical to determining final soybean yield. So how is yield being made in August and how does weather influence it?

Soybeans have several components that contribute to final yield including plants, pods per plant, seeds per pod and seed weight. By August plant population is set, but final pod count isn’t. Soybeans will continue to flower until about August 10 or 12, so some of those flowers can turn into pods with 1 or 2 beans. In addition, some of the later-set pods will abort if the plant realizes it can’t support them.

And during August, many of the pods are still determining their number of seeds and that could range from none to as many as 4 with a plant average of 2.5. So as seed set per pod is being determined, rain is important to set as many seeds as possible. Stress continues to be a major concern in soybean yield during R5 and R6.

Lastly is seed size and weight. Soybean seed varies greatly in size, ranging from 2000 to 3500 seeds per lb. Environment, genetics and position on the plant impact seed size. Seed size is being determined through R6, but not necessarily final weight, which is determined through R7. At the end of this stage full yield potential has been realized and any losses are the result of harvest difficulty.

So August is an important month for soybeans as it determines final pod number and seed number per pod, and contributes to final seed size. Setting up a soybean plant so that it enters August with good health, no nutrient deficiencies, no threat from diseases and insects, and no competition from weeds will help ensure maximize yield potential. Then all we can do from that point on is depend on Mother Nature sending us ample rain.

Agronomist Dr. Daniel Davidson posts blogs on agronomy-related topics. Feel free to contact him at djdavidson@agwrite.com or by leaving a comment below.