Principle of silage making
At harvest, plant cells do not immediately “die”; they continue to respire as long as they remain adequately hydrated and oxygen is available. The oxygen is necessary for the physiological process of respiration, which provides energy for functioning cells. In this process, carbohydrates (plant sugars) are consumed (oxidized) by plant cells in the presence of oxygen to yield carbon dioxide, water and heat: sugar + oxygen ® carbon dioxide + water + heat
Once in the silo, certain yeasts, molds and bacteria that occur naturally on forage plants can also reach populations large enough to be significant sources of respiration. In the silage mass, the heat generated during respiration is not readily dissipated, and therefore the temperature of the silage rises.
Although a slight rise in temperature from 80° to 90°F is acceptable, the goal is to limit respiration by eliminating air (oxygen) trapped in the forage mass.
Some air will be incorporated into any silo during the filling process, and a slight increase in silage temperature is likely. These temperature increases can clearly be limited by harvesting at the proper moisture content and by increasing the bulk density of the silage. Generally, it is desirable to limit respiration during the fermentation process by using common sense techniques that include close inspection of the silo walls prior to filling, harvesting the forage at the proper moisture content, adjusting the chopper properly (fineness of chop), rapid filling, thorough packing, prompt sealing and close inspection of plastics for holes.
Dry matter and moisture
Ideally, corn silage should be harvested at the moisture content appropriate for the type of silo used. Recommended moisture contents are 65–70 percent for horizontal silos, 63–68 percent for conventional tower silos, 55–60 percent for limited oxygen silos, and 65 percent for silo bags.
Corn silage yield and quality as influenced by growth stage.
|Maturity Stage||Moisture %|
Delaying harvest can reduce both the fiber and starch digest bility as the stover gets more lignified and the overmature kernels become harder and less digestible if left unbroken after ensiling. Corn that is ensiled extremely wet will ferment poorly and lose nutrients by seepage, which also has potential to damage the silo and if not contained, contaminate local water supplies. Another problem with chop- ping silage with too much moisture is that a larger amount of lactic acid is needed to reduce the pH. This results in a longer period of time before the silage becomes fermented, producing a lower quality silage. Silage that is too dry may result in poorly packed material, causing more mold and spoilage due to air trapped in the silage. In dry, over mature corn silage, the stover portion of the plant is less digestible and contains lower amounts of sugars and vitamin A. It will not pack well in the silo, more oxygen will be present and it will take longer to get through the aerobic phase into the anaerobic phase of fermentation. Nutrients will be used for respiration during the aerobic phase, the temperature of the silage will increase and possibly burn.
|Parts of plant||Dry matter in early wax ripening|
|Dry matter in early wax ripen ing phase (%)|
The approximate moisture level of chopped silage can be determined by means of a “grab test.”
Squeeze the chopped forage tightly into a ball for 20 to 30 seconds, and then release quickly. For- age chopped into 3/8 to 1/2-inch pieces should be used.
Dry matter is the most important factor for production of good quality silage. The optimal quality silage is produced from components with dry matter contents ranging between 30 and 35%.
In the following table the percentage of moisture in different parts of the maize plant are shown, as well as the ideal time for harvest for silage preparation.
|Condition of the forage ball||Approximate moisture content|
|ball holds its shape and there is considerable free juice||Over 75%|
|ball holds its shape but there is very little free juice||70 to 75%|
|ball falls apart slowly and there is no free juice||60 t0 70 %|
|ball falls apart rapidly||Below 60 %|
Increased moisture or lack of dry matter in silage components should be avoided when possible, as the activity of the lacto-acidic bacteria is decreased and the activity of the butyric acid producing bacteria is increased. The optimal quantity of dry matter is achieved in the last phase of vegetation of the plants. When the weather conditions do not allow timely harvest, resulting in too wet or too dry silage materials, the desired moisture can be achieved by mixing dry and wet components. The composition of the dry and wet components is determined through use of the Pierces’ square as show below:
Example: If you are producing silage from whole maize plants and freshly harvested alfalfa. In the mid- dle of the square you indicate the desired dry matter contents of the silage (for example 30%). On the left side of the square in the upper corner, you indicate the dry matter of the fresh alfalfa and in the lower square, the dry matter of the whole maize plant (45%). By deducting the smaller numbers from the bigger ones, you get the needed percentage of each component that has to be combined in order to achieve the desired dry matter contents. In this case the fresh alfalfa should be included with 15 parts, or 60% and that of the whole maize plant, 10 parts, or 40% of total quantity, resulting in average dry matter of 30%.