Corn Stover and Silage
Corn Stover
Silage
Moisture content of the crop at harvest is likely the most important factor in determining silage quality. If the moisture is too high, the crop will not ensile properly. Wet conditions promote spoilage from heating and nutrient loss (primarily soluble nitrogen and carbohydrates) through seepage and run-off. Wet silage may also freeze during the winter, creating handling difficulties. If the moisture content is too low, the silage will not pack well, thereby holding a larger amount of air for aerobic fermentation. Aerobic fermentation will promote the development of moulds and result in excess spoilage. Aerobic conditions can also produce harder and less digestible kernels.
The fermentation process is fuelled by water-soluble carbohydrates or sugars. In general, the higher the level of sugars, the better the fermentation. All plants contain sugars, some more than others. Sugar content also varies with stage of harvest, often measured by comparing the ratio of the liquid portion of the endosperm to the solid portion, also known as milkline. As a crop matures starch and dry matter increases; however sugar levels decrease.
Enzymes in plant tissues convert nitrates collected from the soil to proteins. During unfavourable growing conditions, these nitrates are not converted as quickly and therefore can accumulate in the plant tissues. Higher levels of nitrates can be a problem in some corn silage piles, resulting in reduced weight gain, and in some cases death. Since plant nitrate levels are regulated by plant growth, factors reducing plant growth may increase nitrate levels. These conditions include:
- Drought conditions – long sustained droughts are less likely to cause problems compared to brief intense droughts. Therefore caution is important after drought-ending rains.
- Cloudy weather – causes reduced plant growth and nitrate conversion rates.
- Extremely high plant populations – reduce cob numbers and nitrate sinks.
- Nutrient deficiencies – such as phosphorus and potassium increase nitrate concentrations.
- Plant age and plant part – nitrates accumulate in the lower, older parts of the plant (4-6”). The stem and roots have higher concentrations than leaves and ears.
- Fields with excess N availability – promote N uptake and increased concentrations of nitrates.
The pH level must be lowered as quickly as possible during the ensiling process to ensure good preservation. Plants with lower sugar contents, such as legumes, are "well-buffered" and resist this change in pH more vigorously than those with higher sugar contents (Table 11). The quicker the pH is reduced the better, as valuable nutrients are burned up during the extended process of lowering the pH in resistant plants. Corn has a high sugar content and thus a low buffering capacity.
Corn | 200 |
---|---|
Ryegrass | 250-400 |
Alfalfa | 400-600 |
Clover | 500-600 |
Ensiling Process
In the period immediately after the silo or bunker is filled, oxygen trapped in the harvested material is used up by respiring plant cells and growing aerobic microorganisms. Moulds and yeasts are usually present during this stage and may grow if conditions are right. Proteolytic enzymes present on the plant tissue are also active at this stage and break down plant proteins into non-protein nitrogen (NPN) compounds such as amino acids and ammonia which are not available for animal gain. The aerobic microorganisms use sugar and oxygen to produce acetic acid, butyric acid, and alcohols. Other by-products resulting from respiration of plant material and microbial fermentation are heat, carbon dioxide (CO2) and water.
The changes of the essential elements of fermentation over time
Anaerobic Fermentation
When sufficient oxygen has been removed from the mass of ensiled material and the acidity has increased, anaerobic microorganisms, which grow without oxygen, such as Lactobacilli and Streptococci, take over as they are more tolerant of acid conditions. Under good ensiling conditions, fermentation will be primarily anaerobic after 3 days. Lactic acid production from these microorganisms will continue to reach its peak until the pH becomes constant at about 4.0 (Figure 22). No further change will occur in the silage if the pH remains in the range of 4.0-4.5 and no further air is permitted to enter the silage mass. If the pH fails to drop below 4.5 or air is permitted to enter the silage, bacteria (primarily clostridia) will convert the soluble carbohydrates and lactic acid to butyric acid which results in the objectionable odour characteristic of spoiled silage. During this type of undesirable fermentation, valuable plant proteins are broken down to produce ammonia, amines, amino acids, fatty acids, and other chemicals thus causing further nutrient loss from ensiled corn.
Harvesting
- The moisture content of the harvested material will ensure minimum yield losses, good fermentation, and low storage losses from seepage or spoilage;
- The yield of digestible energy per unit will be highest; and
- The silage provided will be readily eaten by animals.
The harvesting stage occurs in most growing situations when the whole corn plant contains 30-35% dry matter, or 65-70% moisture. The most accurate method of determining when to harvest is to determine the dry matter (DM) on samples of the whole corn plant. If this is not possible, the producer must be able to recognize the development stage in the corn plant to make a decision on when to harvest. 30-35% moisture is approximately the time when the kernels appear glazed and well-dented and the milk line is 1/4 to 1/2 the way down the kernel (Figure 23). Table 12 illustrates the moisture contents associated with milkline and the resulting quality of silage.
Maturity Stage | Moisture % | DM yield t/ac | Crude Protied % | NDF % 1 | Digestibility & |
---|---|---|---|---|---|
Early Dent | 73 | 5..6 | 9.9 | 48 | 79 |
1/2 Milkline | 66 | 6.3 | 9.2 | 45.1 | 80 |
3/4 Milkline | 63 | 6.4 | 8.9 | 47.3 | 79.6 |
No Milkline | 60 | 6.3 | 8.4 | 47.3 | 78.6 |
1 NDF- neutral detergent fiber |
FIGURE 23 Milkline levels
Moisture content can also be measured with a microwave oven. To test the moisture content, weigh out exactly 100 grams of silage (adjusting for the weight of the dish). Spread the silage evenly on the plate and place in a microwave oven. Heat on high for about 4 minutes (depending on the strength and age of your oven). Remove the silage, weigh and record. Heat the sample again on high for 1 minute. Weigh and record. Repeat this procedure until the weight remains the same. At this point, the weight in grams represents the dry matter (DM) content of the silage. To calculate the moisture content, subtract the DM content from 100. Example: after several heating cycles, the sample weight stabilizes at 34 grams. Thus, the DM is 34% and the moisture is 66% (100-34).
Cutting height is dependent on your equipment and topography of the land the crop is being grown on. Average cutting height is typically set at 4-6 inches. Efforts of raising cutting height to increase silage quality are usually not profitable. Studies have shown that a movement from a 6 to 18 inch cutting height reduced yield by 0.6 t/ac while reducing the NDF by 0.5 - 1%, depending on planting date (Table 13).
Planting Date | Cutting Height (in) | Yield t/ac DM | NDF % | ADF % | CP% |
---|---|---|---|---|---|
Early | 6 | 10.3 | 59.9 | 34.3 | 12.2 |
12 | 10 | 59.6 | 33.9 | 12.4 | |
18 | 9.7 | 59.4 | 33.6 | 12.6 | |
Medium | 6 | 7.6 | 52.4 | 36.5 | 14.8 |
12 | 7.3 | 51.9 | 36.2 | 15.1 | |
18 | 7 | 51.4 | 36 | 15.6 | |
Late | 6 | 5.6 | 55.7 | 33 | 14.1 |
12 | 5.3 | 55.3 | 32.5 | 14.4 | |
18 | 5.1 | 54.6 | 31.8 | 14.8 | |
Abbreviations: DM = dry matter, NDF = neutral detergent fiber, ADF = acid detergent fiber, CP = crude protein. Source: Ballweg, U of WI, 1984. |
Best results with corn silage will be obtained if the material to be harvested reaches the ideal moisture content by maturing before frost occurs. Early planting and early varieties help to ensure reaching the desired maturity while weather conditions are most suitable for harvesting. If your corn crop, which is destined for ensiling is damaged or killed by frost, caution should be taken with the next step. If the corn is only slightly damaged that the leaves remain green and on the plant, dry matter accumulation will continue, and therefore no special instructions are required. It is more of a problem when the plants are killed at a stage too immature to ensile. The plants will likely contain too much moisture for immediate ensiling, and now their dry down will be slow, while dry matter losses accumulate. The best option may be to leave the crop in the field to dry down to the desired level, unless dry matter losses become too high. If the crop is ready for ensiling when damaged/killed by frost, harvest it immediately.
Occasionally corn crops in Manitoba can experience drought conditions. In some cases, drought conditions can be severe enough that growth is unlikely to resume even after a rain. In these cases, corn crops should be ensiled. Net energy content of drought-damaged corn is often 85-100% of normal, and it sometimes contains slightly more crude protein. If drought stress is moderate, corn can often have higher than average energy (in drought years) due to the high grain content and high stover digestibility. However, one must also be aware of the potential for high nitrate levels (see nitrates section). When in doubt, have the feed tested. Drought can also affect the whole plant moisture content. Appearance may be deceiving, as stressed crops may be holding on to more moisture than you think. Consequently, measuring moisture content before ensiling is recommended.
Before deciding which storage technique to use, you should consider volume that is needed, investment costs, structure durability, and ease of loading/unloading. The key to reducing the cost of producing silage is using storage techniques available to you that minimize silage dry matter losses due to air/silage interactions. A few key techniques to reducing these interactions are:
- Harvesting at an appropriate moisture content (Table 14)
- Using higher moisture contents for horizontal silos/bunkers to improve packing
- Filling the silo/bunker quickly with appropriate packing
- Maintaining as little outer surface area as possible
- Sealing the container well
- Feeding at an appropriate rate to minimize open face spoilage
- Maintaining a firm silo face to achieve a seal effect
TABLE 14: Recommended moisture contents for corn silage stored in various types of silos
Soil Type | Moisture % |
---|---|
Upright silo | 60-65 |
Upright "oxygen-limiting" silos | 50-60 |
Horizontal silos | 65-70 |
Bag silos | 60-70 |
When ensiling crop in a pile, it is recommended to size the feed-out face to allow for a daily removal of at least 5 inches from the exposed surface. To calculate the necessary face width (in feet) for this removal rate, multiply the total amount to be fed daily by 12. Then divide the result by the product of multiplying the height of the pile (in feet) times 14.8 (silage density) times 5. Dry matter losses may be 10 percentage points less when silage is fed faster than 5” per day.
Face width needed = (weight of DM to be fed in lbs x 12)
(height of pile in feet x 14.8 x5)
An adequate packing rate in tons per hour can be calculated by dividing the tonnage of the tractor used to pack by 800. A tractor that weighs 26,000 lbs can then effectively pack 32.5 tons of silage per hour (26,000/800). In a 12-hour work-day, this tractor will be able to pack 384 tons of silage while maintaining a reasonable filling speed.
800
Pros and Cons of Corn Silage
- Silage can be harvested in almost any weather conditions
- Higher output of nutrients per acre than grain
- Can salvage crops damaged by hail, frost and high weed competition
- Large quantities of uniform quality feed can be stored
- Handling is mechanized from the field to feed trough
- Requires more labour and time than hay
- Has an odour that may be offensive if stored near populated areas
- Capital investment required for storage facilities, forage harvester
- Has limited market potential. Long distance transportation is inefficient because silage is heavy and deteriorates with exposure to air.
Feed Quality
Feedstuff | Dry Matter Content (%) |
Crude Protein (%) |
Acid Detergent Fiber (%) |
Estimated Total Digestible Nutrients (%) |
---|---|---|---|---|
Corn Silage | 30 | 9.4 | 31.3 | 68.2 |
Barley Silage | 37 | 10 | 34.5 | 63.2 |
Alfalfa Hay | 89 | 16.9 | 37.5 | 58.2 |
Barley (grain) | 88 | 12.1 | - | 82.3 |
Oats (grain) | 89 | 11.3 | - | 79.1 |
Spring Wheat (grain) | 88 | 15.6 | - | 3.72 |
The amount of silage that can be used in a diet for a particular type of animal is determined by the amount of nutrients required by the animal, the nutrient content of the silage, and the amount of silage that will be consumed. The following steps should be used to plan a feeding program that will help ensure that the desired results are obtained:
- Obtain analyses of silage for dry matter (DM), crude protein (CP), and fibre content (ADF, NDF);
- Determine energy value of silage (TDN);
- Decide on performance expected of animals (rate of gain or milk production);
- Determine daily nutrients needed to get this performance by using published tables of nutrient requirements available from Manitoba Agriculture, Food and Rural Initiatives;
- Calculate amount of silage needed to meet the needs of the animals for energy and protein. If the amount of silage is greater than what is likely to be eaten considering the size of the animal and the moisture content of the silage, replace part of the silage with feedstuffs that have higher contents of energy or protein, or both; and
- Feed sufficient supplements to provide adequate supplies of minerals and vitamins to balance the diet. Vitamins A, D, and E may be injected if it is more convenient than feeding in supplements.