Strive to understand how soybeans produce pods and track pod count per plant as a tool to build more yield.
We are into July, and soybeans are producing and filling pods. If you want to increase soybean yields on your farm, track what is happening to pod counts, and see if you can do something about increasing it.
So how many pods does a soybean plant produce? If every node on the main stem and on each branch produced multiple racemes with multiple flowers attached and all those pods survived, a soybean plant could potentially produce more than 1,000 pods. So how come we only count a few dozen pods at harvest?
In the earlier phase of my career, I traveled on the ProFarmer Crop Tour for 7 years. We did not do yield estimates for soybeans (however, ProFarmer made yield estimates based on pod count), but did count plants in 3 feet of row and the number of pods on three plants from within that row. The one thing I noted is soybean pod count averaged between 25 and 40 pods per plant. Sure, we counted as few as 10 and as many as 100 pods per plant, but it still averaged between 25 and 40. So, why are pod counts so low when they can potentially produce hundreds?
When I visited Kip Cullers’ yield plots during the years he hit 139 bushels in 2006 and 156 bushels in 2007 I counted pods and, sure enough, his average pod counts ranged between 100 and 200 pods per plant, quadruple that of the average grower—and his plot yields were quadruple that of the average U.S. yield. So why were his pod counts so high, but still not close to the potential?
I believe one tool to increase soybean productivity is to use pod count as a way to measure change. If you delay planting, you have fewer nodes and fewer pods, and this reduces yield. If you plant earlier, you have more nodes, flowers and pods and higher yield. Other management factors, soil conditions and stress elimination also improve pod count.
When it comes to yield there are four components to consider: plants, pods, seeds per pod and seed weight. These four components contribute to yield, but are indirect yield traits. Because they are compensatory and can change, they aren’t very controllable and aren’t useful as criteria for breeding for yield in soybeans. Instead, breeders rely on yield itself, which is a direct trait that is measurable. Of course, this doesn’t correlate well with pod number.
Soybeans produce a lot of flowers, and about 50 to 70% of them abort. The key is turning more of these flowers into pods. Once a flower forms a pod and it reaches one-quarter to one-third of an inch in length, it will probably survive and fill with seeds. Environmental stress plays a big role in survival as does competition for resources like water, light and carbon dioxide. Minimizing stress and keeping the plant fully fed is the key to maximizing pod set and seeds per acre.
Cullers told me he plants his soybeans early, extends the season, has more vegetative growth, more branches and nodes, flowers and pods, and more and bigger seed, and he feeds that growth. Those were my exact observations when I visited his fields. He has a high population, plants flower early (before the summer solstice) and for a long time, producing a lot of pods. He keeps the plants healthy and green to feed those pods, and he harvests a lot more seeds at the end of the season.
Yield is the total package. Growers need to pay attention to how it’s built and start with a baseline by estimating the number of pods per plant and then tracking it as a measure of a potential increase in yield. While tracking pod counts doesn’t work for plant breeding, it does give growers a tracking tool was they adopt technology to add more bushels.
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Agronomist Daniel Davidson, Ph.D., posts blogs on agronomy-related topics. Feel free to contact him at firstname.lastname@example.org.