Posted on Oct 11, 2017
By Brent Bean, Sorghum Checkoff Agronomist
Pre-harvest sprouting of grain occurs in all crops but is potentially more of an issue in sorghum because of the exposed nature of the grain. Sprouting becomes an issue when the sorghum grain has reached maturity and is exposed to long periods of wet, warm weather. How quickly sprouting will occur is dependent on several factors including the amount and duration of the rainfall, humidity, temperature and wind.
Sprouting occurs following absorption of water through the seed coat that is accompanied with warm temperatures that are sufficient to lead to germination and the emergence of the root radicle. These root radicles are easily observed under close examination of the sorghum head, but following several days of dry weather may become inconspicuous. The grain itself may become discolored, and the inside may take on a chalky texture as the starch and protein begin to break down.
Although differences in hybrids do exist in their ability to resist pre-harvest sprouting, identifying those differences is often difficult because of the variation in maturity that is present in most variety trials. Slight differences in maturity can make a big difference in a hybrid's ability to avoid sprouting with any given weather event.
In evaluating for pre-harvest sprouting, it is easy to overestimate the percentage of grain that has been affected. The entire head should be examined as differences can exist between the top, middle and bottom portions of the head. When evaluating a field for sprouting, look for grain that may have shattered and is on the ground. Even though sprouting may not have occurred, increased shattering has been observed under prolonged wet conditions.
Molds are often associated with sprouted grain. However, mycotoxins are seldom an issue in sorghum, and the incidence of these toxins has not been shown to increase in sprouted sorghum.
The main impact to the grower from pre-harvest sprouting is the potential for lowering of the sorghum grade. Sprouted sorghum falls into the 'damaged grain' classification for grading purposes. U.S. No. 2 grade sorghum can have no more than 5 percent damaged kernels. Grain with greater than 15 percent damaged kernels will fall into the Sample grade classification leading to the grain price being heavily discounted. Additionally, sprouted sorghum can have lower test weight.
A good use for sprouted grain sorghum is for ethanol production, where sprouted sorghum has been shown to be a superior feedstock to non-sprouted sorghum. In research trials, sprouted sorghum had increased ?-amylase activity, degraded starch granules and endosperm cell walls; decreased kernel hardness, kernel weight, kernel size and particle size; and decreased pasting temperature and peak and final viscosities. Most importantly, the time required for sprouted sorghum to complete fermentation was only about half that of non-sprouted sorghum. In addition, ethanol yield was higher (419 L/ton) than non-sprouted sorghum (409 L/ton) on a 14 percent moisture basis.
A second outlet for marketing sprouted or weathered sorghum is cattle feedyards and the poultry feeding industry. Sprouted grain actually has very little impact on the feeding value of grain sorghum. Numerous poultry and cattle trials have shown that feeding value is unaffected in sprouted grain sorghum and in some cases may even be improved.
Photo courtesy of D. Fromme, Louisiana State University