Strategic Planning for Silage Production
To take best advantage of the efficiencies offered by silage, the production of forage and silage should be integrated into a whole-farm plan. When mapping out your strategy, start with your forage sources: is it better to grow a crop that produces a one-off silage cut or choose a pasture or a forage crop that can offer grazing both before and after harvest? If space is tight, would a neighbor be willing to sell their standing crop or pasture to supplement your own production?
When evaluating your options, keep in mind your yield and quality targets as you source your forage options. After all, poor quality forage will never become good quality silage, so the parent crop or pasture should be managed to achieve high yields with high nutrition value. When forage is harvested, it’s best to allow it to wilt in-field for 24 hours to achieve the best moisture profile. Forage that’s ensiled with too little moisture is difficult to compact well and is at greater risk of spoiling.
Built-in Insurance
Some growers identify which fields are destined to silage based on changing circumstances during the growing season. Late plantings and crops subjected to stress from dry conditions, insects, or disease, can be diverted to silage production and make use of situations where high grain yields are unlikely. These practices can serve as a type of crop insurance, but they do limit the use of several management strategies for maximizing yields and quality, such as specific hybrid selection and optimized plant population. In the face of local growing conditions and weather patterns, consider whether the wiggle room afforded by flexible field assignments is worth the loss of maximized production.
Most of the harvesting and ensiling processes can be handled by machinery, but it’s important to budget for the time and manpower required at harvest. Keep in mind that the optimum silage harvest comes before grain and many cereal crops reach maturity, which can alleviate conflicting demands for manpower.
Harvesting for Silage
Ultimately, the final determination of harvest time, no matter which type of forage you’re producing, is the material’s moisture content. Of course, the ideal moisture content varies according to the ensilage technique used, so be sure to research appropriate parameters based on your system. Overall, crops destined for silage should be harvested a bit earlier than crops intended for full maturity, since mature crops are typically drier and the digestibility of fiber and starch is often reduced.
Soil Management
Since crops used for silage, corn for example, leave little crop residue on the soil, concerns like erosion and a reduction in organic matter may lead to lower soil quality and increase problems like lower productivity and more susceptible to erosion. Use of a soil health management system is critical in these instances. Cover crops, reduced or no-till practices, and regular applications of compost and animal manure can help alleviate these issues. When possible, crop rotation can also be effective.
Making Hay(lage)
Haylage is a class of silage made from forage crops like grasses, legumes, or general pasture which could potentially be harvested for hay. Production practices differ slightly from typical silage. For example, harvesting and wilting practices aim for a moisture content somewhere between hay or typical silage. In fact, haylage may require as little as 4 hours of wilting, depending on local conditions. Haylage is usually ensiled in conventional round or medium square bales which are enclosed in a plastic cover, bag, or tube to prevent exposure to oxygen.
Moisture
If forage is too mature or overly wilted, it may reflect a low moisture content. Low moisture content makes fermentation difficult and results in low quality silage. Dry silage also presents problems like overheating, spoilage and fungal growth. Forage harvested when it’s too wet, in contrast, increases the time needed for wilting and winnowing and reduces crop yield.
Speed
When harvesting and ensiling, speed is of the essence. The longer fresh forage spends in the aerobic phase, the greater the risk for heat damage and reduced energy content, so it’s necessary to wrap the product in an airtight cover as soon as possible to eliminate exposure to oxygen and promote rapid conversion to anaerobic (oxygen-free) fermentation.
The Fermentation Process
There are two active stages in the fermentation process, which are common to all types of fermentation, although the specific action and product differ significantly. In most beneficial food applications, alcoholic fermentation and lactic acid fermentation dominate. For example, alcoholic fermentation involves the conversion of carbohydrates and glucose into ethanol, and is featured in wine and beer production.
Lactic acid fermentation, on the other hand, involves the conversion of sugars to lactic acid. This type of fermentation is used in producing pickles, sauerkraut, sourdough bread, yogurt, cheese, vinegar, and silage. This type of fermentation is an effective preservative because many lactic acid bacteria inhibit the growth of a wide variety of food organisms that cause spoilage in food products.
Interestingly, the consumption of small amounts of fermented products containing lactic acid can help lactose intolerant people. (For humans, we recommend consuming yogurt, not silage!)
The production of high quality silage is controlled by five main factors
- Moisture content of the fresh forage
- Fineness of chop
- Exclusion of air
- Forage sugar content
- Bacterial populations (both natural and supplemental)
Aerobic phase
Beginning as soon as forage is mown, plants begin the first stages of aerobic fermentation, including the breakdown of proteins by plant enzymes and an increase of aerobic bacteria populations. This process consumes oxygen and water-soluble sugars stored in plant tissues, producing carbon dioxide, water, and heat. This process usually lasts 3-5 hours, depending on how well the material is compacted and how quickly it’s sealed within a storage structure. This stage should be kept as brief as possible to maintain silage quality. Excessive aerobic fermentation reduces energy content and may cause protein damage from exposure to high temperatures.
Anaerobic (Fermentation) Phase
Once the available oxygen has been consumed, aerobic bacteria die and anaerobic bacteria begin to multiply quickly. This marks the beginning of lactic acid fermentation. Lactic acid lowers the pH of silage, which is needed to create stable, high-quality silage. This increasing acidity contributes to an environment which, coupled with lack of oxygen, helps prevent growth of undesirable microbes like clostridia, yeasts and molds.
Anaerobic fermentation may last three or four weeks, after which the silage reaches a stable state. This state is achieved when the pH becomes so low that no microbes can grow. High populations of lactic-acid producing bacteria will quickly achieve this state. Inoculation of forage prior to ensiling can ensure that lactic-acid producing bacteria dominate the anaerobic stage from the beginning.
