Soybean School: Why August rain makes soybean yield


August rains make soybeans — it’s more than just a cliche, it’s a crop management fact that rings true whenever timely moisture finds soybean fields during a pivotal growing month for the oilseed crop.

On the episode of the RealAgriculture Soybean School, AGRIS Co-operative senior agronomist Dale Cowan tells us why and how August rains play such a key role in soybean yield. It all comes down to the plant’s root system, says Cowan who points out that more than 80% of the plant’s root mass is still located in the top three inches of soil during this key growing period.

The tap root may extend one foot or more into the soil but a mass of shallow lateral roots are doing most of the heavy lifting and providing the plant with nutrients and water, explains Cowan.

In a dry August, the plant really struggles, but when rain arrives, roots lurking just below the soil surface can quickly carry moisture and nutrients to pods in the R5 and R6 stage to fill beans and make yield.

But those timely rains will only deliver strong yields if plants have developed sufficient yield potential — a lot depends on how many main stem nodes you have and the number of beans on a pod when the rain arrives. Most of the nodes on the plants Cowan inspects in the video have to two to five pods, but there are many flowers on nodes that didn’t make pods, he notes. Unfortunately, August rains won’t help them contribute to final yield.

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