Sorghum (Sorghum bicolor) is a warm-season grass that ranks as one of the world’s most important cereal crops. Cultivated for over 3,000 years, primarily in Africa, this resilient plant thrives in regions with high temperatures and limited water, often outperforming corn in drought conditions. Sorghum is utilized for its grain in human food, animal feed, and ethanol production, while the stalks and leaves are used for forage or syrup. Successfully moving the grain from the field to storage requires careful timing and specific techniques to preserve quality and maximize value.
Identifying Sorghum Maturity
Determining the precise moment for harvest involves recognizing the difference between physiological maturity and ideal harvest maturity. Physiological maturity is the point when the kernel reaches its maximum dry weight and stops accumulating nutrients from the plant. This stage is visually confirmed by the formation of the black layer—a small, dark spot at the base of the kernel where it attaches to the head.
At physiological maturity, grain moisture content is typically high, ranging between 25% and 35%. Harvesting at this level is not recommended because the soft seeds are highly susceptible to damage during threshing. For mechanized harvesting, the goal is to allow the grain to dry down naturally in the field to a moisture content of 17% to 20%. This range is the most economically efficient target, as harvesting above 25% moisture can result in excessive field losses or cracked grain.
Manual Harvesting Techniques
For small-scale growers, manual harvesting is a practical method. This process involves using a sharp tool, such as a sickle or knife, to cut the grain-bearing heads (panicles) from the stalks. The heads are typically cut when the grain is slightly high in moisture (16% to 20%) to minimize shattering losses in the field.
Once collected, the panicles are dried further before the grain is separated. Threshing, which separates the kernels from the chaff, is accomplished using mild abrasion. This can involve placing the dried heads in a sack and beating them gently or rubbing them against a hard surface. The loosened grain is then separated from the remaining plant material by winnowing, which uses air current to blow away the lighter chaff.
Mechanical Harvesting Techniques
Commercial sorghum production relies almost entirely on large-scale mechanical harvesting using a combine harvester. Producers typically use a standard grain platform or specialized row-crop header to gather the heads. To maximize efficiency and minimize wet stalk material entering the combine, the header is usually set to cut the plant just below the grain head.
Properly adjusting the combine’s internal components is essential to prevent excessive grain damage. The cylinder speed must be set lower for sorghum than for grains like wheat to avoid cracking the small kernels. The concave clearance—the distance between the cylinder and the concave surface—must be set wide enough to roll the head and gently release the seed. These precise adjustments ensure the grain is thoroughly separated while minimizing wet plant residue carried into the hopper.
Essential Post-Harvest Handling
The immediate handling of the harvested grain is a determining factor for its long-term quality and storage safety. Grain sorghum frequently contains more trash, such as pieces of stalk and leaves, than other grains, especially if harvested before a killing frost. This foreign material must be removed using cleaning equipment, as it inhibits airflow during drying and introduces moisture that leads to spoilage.
The central task after harvesting is to reduce the grain’s moisture content to a safe level for storage, typically 13% to 14%, and 12% for storage longer than a year. If the grain was harvested above 16% moisture, heated air dryers (such as batch or continuous flow systems) are necessary to quickly lower the moisture content and prevent mold or sprouting. For grain below 16% moisture, supplemental drying can be achieved using natural air aeration, provided the fans deliver sufficient airflow to overcome the high resistance of packed sorghum kernels. Once dry, the stored grain must be consistently monitored and cooled through aeration, which prevents moisture migration and subsequent spoilage.