Comparing Sorghum Silage vs Corn Silage

Introduction

When looking at the benefits of using a sorghum silage compared to a corn silage, it is important to understand that there are different sorghum products available that can be used for silage production. Each sorghum product has advantages and disadvantages, including differences in maturities, tonnage, feeding values, disease tolerance, harvest considerations, cost of production, and water savings. Other benefits of growing a sorghum product for silage are better drought and heat tolerance compared to corn.

Benefits of growing a sorghum silage compared to a corn silage:

• Water savings – sorghum is drought tolerant and water efficient
• Variety of maturities available – 40-day to 120-day maturities
• Production cost savings – seed cost is less and irrigation pumping costs are reduced
• Heat tolerant – corn development stops when temperatures reach 86 °F, but sorghum continues to develop in temperatures up to 100 °F

Several of the more popular sorghum products used for silage include:

Forage sorghum – This is a taller, high-tonnage version of grain sorghum that is drought-tolerant. Types of forage sorghums include:

• Conventional – 10 to 12 ft tall grain-type forage that is often fed in beef feedlots or to dry dairy cows (not producing milk).
• Brown Midrib (BMR) – BMR sorghum silage products contain a gene that reduces the lignin content and increases the fiber digestibility. Because of the higher fiber digestibility, this forage sorghum is often competitive with corn silage when it comes to digestibility on a milk per ton basis.
• Photoperiod sensitive sorghums – These sorghums are tall forage plants that do not produce a grain head because the plants do not start the reproductive growth stage until day length is shorter than 12 hours and 20 minutes.¹ Since no grain is produced in most growing areas, the starch levels are very low in this silage and the feed energy is stored as sugar. Most photoperiod sensitive sorghum products need to be swathed and wilted to get to a proper ensiling moisture.
• Brachytic dwarf – six to eight feet tall sorghum product. This shorter forage has the same number of leaves but with shorter internodes and may have fewer lodging problems than taller sorghum products.
• Dry-stem forage sorghum – This forage sorghum type has been bred to have lower whole plant moisture at the soft dough growth stage. In some production areas it can be direct cut, with no need to be swathed and wilted to get the silage to the correct whole plant moisture for proper ensiling.
• Large-seeded forage sorghum – bred to have a large seed size when harvested at the soft dough growth stage to improve kernel processing, which can improve starch availability.

Sorghum-sudangrass – This drought-tolerant plant type has a wider leaf and a courser stem than a true sudangrass but with higher tonnage potential. It can be harvested several times during a growing season, though in most cases it needs to be swathed and wilted, or a frost is required before it reaches a low enough whole plant moisture level for optimum ensiling. Since this product is most often harvested at the late vegetative or early reproductive growth stage, it can have high protein levels, very low starch levels, and its feed energy is stored as sugar. With a wide range of maturities ranging from 40 to 120 days along, these products are fit for many production scenarios, such as when there is a need for an early silage feed source. Many of the different plant characteristics that are available in the forage sorghum product lines are also available in sorghum-sudangrass products. Some products are now available with sugarcane aphid (also known as sorghum aphid) tolerance, which reduces the potential for problems with this pest.

With all these options and benefits to growing a sorghum silage, why is corn silage often the preferred feed for cattle? Corn silage is widely considered the forage crop with the most energy per acre, at least compared to other silage options. The high energy per acre is important for any cattle producer growing silage for their cattle feeding needs, either on acres controlled by the dairy or feedlot or when silage is contracted from local farmers, by the acre or ton. Corn silage is also often preferred because it provides a balanced and cost-effective feed option for cattle operations.

Why replace a corn silage product with a sorghum silage product?

When comparing the advantages of growing corn silage with the advantages of growing sorghum silage, what is often the deciding factor that convinces a farmer to change their silage acres from corn to sorghum? The answer to this question can be extremely complicated, but in many areas, it comes down to needing a silage option with better drought tolerance and water efficiency than corn. Some of these farmers are in areas where the availability of irrigation water is growing scarcer by the year, a situation exacerbated by frequent droughts. These water-limited places are often the same areas that are still growing in cattle numbers, because they have a historic advantage for beef and dairy production. The growing need for a consistent source of forage for these areas is what often forces these cattle producers to move away from corn and replace their acres with sorghum silage.

The amount of water needed to grow a sorghum silage crop varies depending on the product and the maturity length of the sorghum chosen. Sorghum silage products often vary between 40 and 126 days to harvest, and sorghum silage is often grown on just over a half to a third of the water needed for a comparable yield of a corn silage crop.² Additionally, hauling a silage source is much more expensive than hauling a concentrated feed source like grain due to the higher water concentration of the silage, which is often 60 to 70% water. This cost makes it important to source a silage crop near dairy and beef cattle feeding operations.

Comparing Feed Values

In general, the feeding value of forage sorghum silage is often about 80 to 90% of corn silage.⁴ However, it is difficult to compare the feed values of sorghum silage and corn silage due to the variation in feed values among different sorghum silage products and the different growth stages at which these products are harvested. Because of these differences, corn and sorghum products should be compared on a product-by-product basis.

These silage sources are generally similar in protein content, but sorghum is lower in energy because sorghum products are often much lower in starch than corn. A good corn silage can be 25 to 35% starch or higher, while a grain-producing sorghum silage is often between 11 and 15% starch. "Starch availability is an important factor to consider when deciding between these two plants as it can directly impact feed intake, milk production and component levels," notes Dr. Margaret Winsryg, Idaho-based technical support specialist with Calibrate^® Technologies.³ However, sorghum silage often has higher sugar levels than corn silage, and these sugars are also a good source of energy. Because sorghum produces sugars through the vegetative and reproductive growth stages, the sugars are ensiled and stored for cattle to utilize. If harvest is delayed, sugar levels can drop as the sorghum grain reaches maturity (Figure 1).

The hard, small kernel that sorghum silage often has if harvested at or after the soft dough growth stage can also reduce sorghum’s feed value compared to corn.⁴ Even when sorghum silage is harvested in the soft dough growth stage and with a chopper using a silage processor, it is very difficult to get good kernel processing due the small grain size of most sorghum kernels. However, using some of the newest sorghum silage products can produce silage with high feed values equal to that of corn, especially when both crops are grown in high stress environments.¹ In this situation, a high tonnage sorghum silage product with high fiber digestibility and sugar levels can compete with the energy supplied from the starch in a corn silage.

Because various products have different nutritional values, it is important to understand how they will be used in different rations to properly supply the nutritional requirements for different types of cattle. For example, high milk-producing dairy cattle need different nutrition than dry cows or growing dairy heifers. Similarly, a beef steer in the last months of the fattening cycle has different nutritional needs than a mother cow or a lightweight steer that was recently weened.

Historic reasons why a farmer would not replace corn silage with sorghum silage:

• Forage sorghum grows too tall and lodges before harvest.
  • Newer sorghum silage products available in a dwarf or Brachytic dwarf plant styles have been bred to reduced plant height to six to eight feet tall at harvest, and these products now have dramatically reduced lodging problems.
• Forage sorghums do not have the feed quality of corn silage.
  • With the introductions of BMR products, the lignin content of the sorghum has been reduced. Reducing lignin has helped increase fiber digestibility, which subsequently increases total digestible nutrients (TDN), in vitro true digestibility (IVTD), and neutral detergent fiber digestibility (NDFD), meaning the feed values of sorghum silage products are competitive with the feed quality of corn silage.
• Whole plant moisture of sorghum silage is too high to direct chop sorghum for silage, which is how most corn silage is harvested.
  • Some of the newer sorghum silage products, including the dry-stalk products which reduce the whole plant moisture content at the soft dough growth stage, now allow a silage farmer to direct chop some of these products, depending on the storage structure used to ensile and store the silage.

Conclusion

It is especially important to understand that sorghum silage is not a one-to-one replacement for corn silage for all cattle operations. Rations should be rebalanced to meet the nutritional needs for each cattle type when changing from a corn silage source to a sorghum silage source. While a sorghum silage source can fit many beef and dairy cattle operations it can be critical to choose the right sorghum product for the type of cattle that are to be fed, as no one product fits all feeding sicarios. Managing the quality of any crop harvested as a silage feed source requires that crop to be harvested with the correct management steps to properly ensile, including harvesting the crop at the correct crop maturity, with the correct whole plant moisture content for the type of silo or structure for storage, the correct chop length, packing rapidly and adequately to remove oxygen, and using a good plastic seal to keep oxygen out during storage. Lastly, with the substantial number of sorghum silage products available and their individual characteristics, some cattle feeders may require different sorghum seed sources for their feed needs.

Sources

¹ Marsalis, M.A. and Bean, B. 2016. Western forage production handbook. United Sorghum Checkoff Program. https://www.sorghumcheckoff.com/production-guide/western-forage-production-guide/

² Kidd, T. 2016. Sorghum silage: An alternative to corn. Progressive Dairy. Feed management. https://www.agproud.com/articles/25221-sorghum-silage-an-alternative-to-corn#:~:text=One%20of%20the%20ways%20forage,achieve%20yields%20comparable%20to%20corn.

³ 2014. Sorghum silage or corn silage? Dairy Herd Management. Calibate Technologies. https://www.dairyherd.com/news/sorghum-silage-or-corn-silage

⁴ (Jenkins) Wilke, K. H. and Drewnoski, M. 2022. What to expect from alternatives to corn silage. University of Nebraska – Lincoln. Institute of Agriculture and Natural Resources. UNL Beef. https://beef.unl.edu/beefwatch/2022/what-expect-alternatives-corn-silage#:~:text=Forage%20sorghum%20silage%20is%20about,less%20grain%20in%20the%20silage

Web sources verified 09/27/2023 1127_297151