Manage sorghum’s unique characteristics

Posted on March 10, 2022 in Forage Foundations
By Cody McCary, Vita Plus forage specialist
I have had the opportunity to work in many areas of our great country and observe how farmers have adapted to their region’s unique growing conditions to achieve their forage program goals. One alternative forage that I have seen proven useful is sorghum.

While this is by no means an exhaustive list, here are some important items to consider when determining if sorghum may fit into your forage program.

1. Varieties
Varieties of sorghum include, but are not limited to, grain sorghum, forage sorghum and sorghum-sudan. For the purpose of feeding dairy cattle, we most often discuss forage sorghum and sorghum-sudan. Forage sorghum is typically harvested for silage in a one-cutting system while sorghum-sudan may be harvested in multiple cuttings for green chop, silage, or hay because of its rapid regrowth and potential tillering.

2. Plant variation
The physical appearance of sorghum varies.  For example, some forage sorghum varieties may reach an approximate height of 10 to 14 feet while sorghum-sudan often achieves a more intermediate height of approximately 5 to 7 feet.  This physical diversity allows for a wide range of choices to meet current needs.

3. Nutritive value
Nutritive value differs based on the variety and hybrid selected. In general, sorghums typically contain greater concentrations of crude protein, NDF, ADF, and lignin and reduced NDF digestibility in comparison to corn silage. Starch concentration of sorghum silage is lower when compared to corn silage. Just as in corn grain, sorghum grain contains an outer seedcoat and a starch-protein matrix that inhibits starch digestion in dairy cattle. We know that mechanical processing of corn silage to break kernels is important in improving starch digestibility; an assumption can be made that similar mechanical processing techniques must be applied to the grain in sorghum silage to achieve maximum ruminal starch digestion.

While working toward my master’s degree at the University of Florida, I tried to test this assumption by growing sorghum and processing the plants with a forage harvester. During harvest, we used combinations of a 1- or 3-millimeter roll gap setting and a 15- or 22-milimeter chop length setting. Aggressive processor settings increased the proportion of sorghum grain passing through a 2.36-millimeter sieve. This sieve represents sorghum grain broken in two or more pieces. However, very few samples reached 50% of starch passing through this sieve, and in situ starch digestibility values were very low even after 90 days of fermentation.

This is only one study, but results highlight the resistance of the grain in sorghum silage to mechanical processing. More aggressive processors and/or settings might have had a positive impact on sorghum grain processing, but further reducing the roll gap width would have slowed harvest, reduced throughput, boosted fuel costs, and caused more wear on grain processing rollers. To maximize starch digestion in sorghum grain, continued research is needed to better define and understand harvest recommendations.

4. Trait selection
Brown mid-rib (BMR) and brachytic dwarf traits are available. Brachytic dwarfing reduces the internode length, effectively shortening overall plant height and increasing standability when compared to taller non-dwarf counterparts. BMRs have exhibited increased NDF digestibility and, in some cases, achieved similar NDF digestibility to that of conventional corn silage.

5. Harvest timing
Harvest timing affects nutritive value. For example, by harvesting at an earlier maturity (i.e., boot versus soft-dough stage) additional improvements in crude protein concentrations and improved fiber qualities may be captured, but yields will be negatively impacted.

These five items are the start of things to consider when determining if and what varieties of sorghum fit your farm.  Decisions should be based upon your specific situation and the needs of your forage program at the current time. Work with your agronomy and nutrition consultants and take the time to carefully select forages that help you achieve your forage program goals.

Category: Crop varieties
Forage Foundations
Forage harvesting