Many farms grew sorghum or sorghum species for the first time this summer. Its harvest timing is very different than corn silage if you want to get it right.
Sorghum can be a wetter, high-sugar, low-starch forage. In a properly balanced ration, sorghum can produce the same amount of milk for less cost. But chopping it short or processing it will produce forage that will be the consistency of applesauce or soup. This is not beneficial for good fermentation, high milk components or preserving nutrients.
The good news is that there are five steps you can take to maximize results and minimize potential problems:
1. Don’t wait for it to mature. Our replicated research, supported by the New York Farm Viability Institute, looked at various harvest stages of BMR sorghum. The results were analyzed by Larry Chase, emeritus professor of animal science at Cornell, using the Cornell Net Carbohydrate and Protein Systems model.
We found that for seeded-type sorghum, the potential milk increased from the boot stage as the fertilized seed heads started to fill. Milk potential decreased when we went from the tip of the seed head just starting soft dough to soft dough halfway down the head because of a significant decrease in fiber digestibility where a lot of energy is stored. This is compounded by the loss of energy in hard, undigestible seeds.
Thus, waiting for matured grain can decrease milk production. Replacing corn silage with sorghum is not just about throwing in sorghum silage and calling it a day.
The ration must be rebalanced to a high-fiber feeding level. In general, a slight amount of additional cornmeal is added for energy and a similar amount of protein supplement is removed as sorghum can have higher protein than corn silage.
Research has found that sorghum-based rumen pH is higher, which enables higher components and less potential for subclinical acidosis.
There is no advantage to waiting for more mature grain with forage sorghum. In Texas and the South, they wait until the soft dough stage is halfway down the seed head. But there are major disadvantages to using this technique in our area.
The first is lodging, which increases dramatically as the seed head matures. In our research, we have found that even the lodging-resistant brachytic dwarf BMR sorghum fell down a week after the tip of the seed head moved to the soft dough stage.
Second, if the seeds move to a harder dough stage, they are the size of birdshot and can’t be digested. Processing does not help this at all, and research shows that even if they are broken, they are hard to digest.
This means that sorghum is ready for harvest before it gets to 35% dry matter, and many times when the tip reaches soft dough, it will only be reaching 30% dry matter.
Our research has found that with proper steps, we can make perfect sorghum silage at dry matters as low as, or lower than, 25% with no butyric acid.
2. Chop low and slow. Directionless corn heads will chop sorghum effectively, especially if the plant is more than 4 feet tall. We have directly chopped sorghum, sorghum-sudan, sudangrass and pearl millet; the key is that the harvesting head needs to be down on the ground to get as much of the crop as possible as it is all highly digestible forage.
The knives must be sharp, or they will simply knock it over and contribute to plugging. Also, watch your forward speed as sorghum is easy to chop, and there is a tendency to drive faster. If you do this, you will quickly pass the cutting speed of the head and start leaving longer stubble in the field.
Longer stubble is an immediate 10% to 15% yield loss of highly digestible forage from driving too fast. Going too fast also contributes to plugging. Plants that do not have a stem or head emerged, and are shorter than 5 feet, will be all leaf and may not chop well. These fields may need to be mowed to a windrow and chopped with a haylage head.
We don’t suggest trying to dry it wide swath as it is too thick to dry and impossible for tedding. Farmers have told me that the merger had to go the opposite direction that the swath was mowed for it to feed in and merge properly. A sorghum wide swath will also mix more dirt and contaminates when you try to rake or merge to a windrow.
3. Watch your length of cut. The length of cut that the chopper is set is critical. Richard Grant of Miner Institute has found that as forage quality decreases, a shorter length of cut will result in greater milk production from poorer forages. The reverse is true for highly digestible forages such as flag leaf triticale and BMR sorghum species.
The smaller they are chopped, the faster they are flushed out of the rumen before you get the full extent of digestion. Larger particles will stay entrained in the rumen mat until the rumen bacteria extract most of the nutrient components.
The other problem with chopping these silages fine is it increases the number of plant cells cut open and will release hundreds of gallons of leachate. Besides making a smelly mess, leachate removes the most digestible part of the plant. Each additional cut (shorter chop length) opens more plant cells for the liquid to run out.
We harvested at half, three-quarters and 1.14-inch length of cut with no processing. As long as we did not process, we had excessive leachate from the half-inch, but not the three-quarters inch or 1.14-inch. A cut length of a minimum of three-quarters inch, and preferably 1 or more inches, seems to work best.
4. Don’t process it. We strongly suggest no processing. At the stage we harvest at — seeds at the tip just becoming like cooked oatmeal — processing does nothing to improve feed value and increases leachate more than fivefold.
An added benefit from not processing is that there is significant sugar conserved through fermentation as it reflects less cell rupture, preserving the nutrients within intact cells of wet forage until opened by rumen digestion. If the processor is difficult to remove, then open it as wide as it will go.
5. Use an inoculant for ensiling. People start to freak out when we talk about making wet silage. Nearly all their experiences are with crops that didn’t dry after being left in the field for three or four days. Respiration removed all the substrate and even inoculant could not help.
It can also occur with a forage crop that’s been harvested wet the first sunny day after an extensive cloudy stretch. The clouds keep photosynthesis production less than respiration consumption, and the plant has a negative substrate to support fermentation. It becomes a smelly mess that the cows don’t want to eat and will perform poorly on.
Wet, high-sugar sorghum is different. It has a very high substrate to support complete fermentation. We had excellent results ensiling sorghum as low as 17% dry matter with no butyric formation. The critical step is to not make sorghum silage without an inoculant.
Don’t grow and harvest highly digestible forage and let whatever garbage is floating in the air that day do the “fermentation.” If the crop is below 30% dry matter, don’t use a first-generation buchneri-type inoculant. A homolactic fermenter is better.
There is a next-generation inoculant with a unique buchneri strain combination that handles wetter, high-sugar forages very well in our replicated sorghum research.
Kilcer is a certified crop adviser in Kinderhook, N.Y.