Hear that? If you shake soybean plants and hear the rattle of seeds in the pods, the plant has reached physiological maturity. Does that mean the crop is ready to harvest or past being damaged by frost? Not so fast.
In this Soybean School video, Kristen Podolsky, production specialist with the Manitoba Pulse Growers Association, walks us through the various stages of crop maturity — from green, to physiologically mature, to ready to harvest (see the photo above for an example). Podolsky also discusses how long each maturity stage can take to move through, the risk of frost and the extent of the damage at each stage, plus she offers tips on evaluating maturity and harvest-readiness of the crop.
Frost damage remains a costly risk until the crop is physiologically mature. A light frost of around zero degrees C may only affect top growth while a harder frost, -2 degrees C or colder, can affect pods and seeds — anything that is still green at the time of frost. The key is to have the crop well into maturity before frost happens, which is most likely in mid September for Manitoba. Farmers with still-green crops at this point in the year may need to re-evaluate their variety selection, as extensive yield loss can occur at this point.
Soybeans should be harvested around the 13% moisture mark, Podolsky adds — too dry puts the crop at risk of cracking, even though the damage may not be noticeable. Again, dry down time can range depending on the weather, so careful monitoring is required.