September 2023
HP Article

Brent Bean, Sorghum Checkoff Director of Agronomy

Once a hybrid has completed flowering the grain begins the process of adding dry matter. Initially grain moisture is 80 to 90 percent and decreases as starch is accumulated. Once the grain fully colors and reaches the hard dough stage, moisture content is 50 to 60 percent. Over the next few days, under good growing conditions, starch accumulates rapidly while moisture decreases, reaching physiological maturity in approximately 10 to 14 days. Hybrids may differ in grain moisture when they reach physiological maturity, which can be identified when a black layer or spot is visible at the base of the kernel.  Grain moisture at this time may vary from 25 to 35 percent depending on the hybrid and environment. 

A common question in September and October is how fast will grain sorghum dry down after it reaches black layer?  Researchers at Kansas State University conducted an excellent trial examining sorghum grain filling and dry down dynamics of 20 hybrids in 2018 and 2019. The average daily dry down was 0.76 percent of moisture per day with a range of 0.64 to 0.99 percent per day.  The number of days from black layer to achieving a grain moisture content of 14 percent was 23 days with a range of 16 to 32 days, depending on the hybrid and year.

The rate of dry down in any given environment depends on a number of factors, but most importantly are temperature, humidity and air circulation.  Warmer temperatures expedite moisture evaporation from the grain, while high humidity levels will slow down the process. In addition, air circulation from wind enhances drying efficiency.  It also helps if rainfall is absent during this time. Grain head architecture may also play a role, with a compact head drying a little slower than a more open panicle. 

A common misconception is that applying a harvest aid will speed up the drying of the grain. This is not the case. What harvest-aids, such as glyphosate or sodium chlorate, will do is dry out the leaves and stalks facilitating timely and efficient harvesting. Eliminating some of the green stover material that ends up with the thrashed grain may slightly lower the percent moisture being measured, but has little impact on actual grain moisture.