By Hans Kandel
Extension Agronomist Broadleaf Crops
The soybean plants are rapidly moving to maturity. The loss of green pod color is a reliable indicator of maturity. Stage R7 according to Fehr and Caviness occurs when one normal pod on the main stem has reached its mature color. Physiological maturity (growth stage R8) is reached when 95 percent of the pods have obtained the mature pod color which can be brown, golden, yellow, or gray depending on the variety. The seed moisture will be around 35 percent. At physiological maturity the seeds will not add anymore dry weight and just have to dry down for harvest. In the NDSU soybean variety trial information the date when a variety is physiological mature is provided, unless otherwise indicated in foot notes.
Individual pods can also be checked and when the beans are separating from the white membrane lining the pod, the beans will not gain anymore dry matter. Maturity can be determined on a plant or field basis but often there is variability in the maturity in the field due to differences in the growing conditions. In a drier field, the soybean bean plants in the lower areas tend to stay green a little longer. At 95 percent mature pod color on a plant it may take 4 to 6 days to have all pods reach the mature color. It will take about another 2 weeks (depending on temperature and humidity) to get down to harvestable moisture levels. Harvest delayed to less than 13 percent moisture may cause an increase in pre-harvest shatter losses, sickle-bar shatter loss during harvest, an increased number of split beans, as well as a loss of soybean weight to sell.