Maximizing Profits With Bunker Silos

Moveable Wall Bunker Silos

Maturity

Conclusions

References

Silage Moisture

Theoretical Length of Cut

MAXIMIZING PROFITS WITH BUNKER SILOS

Dr. William P. Kautz

Director of Product Development and Technical Services

Chr. Hansen BioSystems

Milwaukee, Wisconsin

INTRODUCTION

Bunker silos have been used successfully for many years, especially in the western United States by large feedlots and dairies. Expansion of dairies in other parts of North America has led to a large increase in the number of bunker silos. Bunkers offer the producer large storage capacity at a relatively low cost. If managed correctly, bunkers can be nearly as efficient as other types of silage storage structures. (Table 1) The goal when utilizing bunkers in a feeding operation is the same for any other type of storage structure - to minimize the losses that occur during harvest, storage and feedout through proper management techniques.

Table 1. Average (and typical range) of DM losses associated with ensiling systems

Storage type

Trench

Stack

Horizontal Bunker

Concrete Tower

O2 limited tower

Bag

Round Bale

% DM

Loss type _________________________% DM Losses______________________________

Source: Alberta Agriculture, 1988

BUILDING A NEW BUNKER

When building a new bunker, consider the site. Forages should be stored near commodities and grain to reduce labor costs associated with feeding. Bunkers should have a minimum of a 2% slope to facilitate drainage. The lower end of the bunker should be located in a well drained and graded site. Make sure there is plenty of room for unloading equipment, feed trucks and wagons.

Bunker floors are usually concrete, although some operators have constructed bunkers with floors made of high grade asphalt with a crushed gravel base. The costs of the two types of floors, when properly built, will be similar. Some experts feel that asphalt will resist silage acids better than concrete and potentially have a longer life. Poor quality asphalt should be avoided. Heavy equipment will damage or destroy poor quality material, especially in hot weather.

If a trench is dug into the side of a hill, it may be possible, with heavy soils, to eliminate concrete walls. The author has observed that trenches without walls tend to be more difficult to manage. Spoilage and subsequent losses along dirt walls tend to be higher than with concrete walls. A floor, however, is absolutely necessary even with a hillside trench. Dirt floors have generally failed, especially in areas that normally receive substantial amounts of rain and/or snow.

There are many different styles of bunker walls available. Consult with local contractors, but be sure to work with an expert when choosing the type of wall. Walls should be built as high as possible, keeping in mind that the top of the silage mass should be within reach of available unloading equipment. Building walls higher than unloading equipment will make it much harder to manage the face properly on feedout and can result in dangerous overhangs. Minimum height is 8 feet but many bunkers have been built with walls 16 feet and higher.

Another good rule of thumb is to build bunkers as narrow as possible. This is done to minimize the surface to volume ratio in the structure and can result in a significant reduction in dry matter losses when the silo is properly managed.

There is often a tendency to build bunker silos too wide. When designing new bunkers, plan to feed six inches across the entire face on a daily basis. Use the following formula (Ruppel, 1997) to calculate bunker width:

Width (Ft.) = [12 x Amount Fed] ¸ [Silo Height (Ft.) x Silage Density x 6]

Note: Amount fed (lbs. per day) and silage density (lbs. per cubic foot) can be expressed

on either an as fed or dry matter basis but both must be the same. Densities

of bunker silos will vary with the amount of packing. Average values are 14.8

pounds dry matter per cubic foot for haylage (Ruppel et al., 1995) and 17.7

pounds dry matter per cubic foot for corn silage (Holter, 1983).

When bunkers are built above ground, it is best NOT to put in a back wall. Experience has shown that it is difficult to sufficiently pack material in the corners and along the back wall. This usually leads to excessive spoilage and dry matter loss in the last 10-15 feet. Not building a back wall will reduce bunker capacity slightly but will allow good packing of the entire silage mass. It also allows the operator the option of feeding from both ends of the silo if desired.

The use of moveable L-walls or T-walls has several advantages for a producer who is expanding or wants more flexibility in feed management. Moveable walls allow the producer to size the bunker face so that at least 6 inches of material can be removed from the silo each day. This type of structure allows the producer to size silage bays in relation to the volume of the anticipated crop. Other advantages include access to each individual crop when mixing rations, continued feeding of fermented silage while filling other bays, and complete feeding of current crop before moving into next year’s crop.

HARVESTING THE CROP

The silo should be filled with material that is cut at optimum maturity, moisture and chop length to insure good fermentation and high quality forage. Proper maturity is important to make sure the maximum amounts of nutrients are available to the animal during feedout.

Proper maturity assures adequate fermentable sugars for silage bacteria and maximum nutritional value for livestock. Maturity also has a tremendous impact on moisture with unwilted forage crops such as corn silage. Another concern with maturity involves providing forage sources with acceptable levels of fiber and starch. Variation in fiber digestibility can vary from 30-50% for traditional forages such as alfalfa and corn silage, and can affect the energy content of the ration, microbial production and laboratory prediction of energy content. It also may greatly affect dry matter intake under some feeding situations. Ruminal fermentation of starch varies from less than 50% to over 90% for grains, depending upon plant source, plant maturity and processing. Variation in rumen fermentable starch can affect rumen pH, dry matter intake and microbial protein production (Mahanna, 1997).

Proper moisture is necessary to ensure optimum packing and removal of oxygen. With most crops 63-68% moisture is optimum. Material can be ensiled at less than 60% moisture, but increased packing time will be necessary to remove oxygen. Avoid moisture greater than 70% with alfalfa haylage if possible. Ensiling alfalfa at high moisture significantly increases the risk of a poor quality fermentation. Clostridial organisms proliferate at high moisture and produce butyric acid. These organisms also seriously degrade protein and produce compounds and silage unacceptable for high producing cows. The best way to avoid this type of fermentation is to field wilt alfalfa to less than 70% moisture.

The best compromise between fermentation requirements and cow rumen function demands is a chop length of between 1/4 to 1/2 inch theoretical length of cut (TLC), depending upon the crop. These chop lengths allow for proper silage compaction, oxygen exclusion, ease of unloading and adequate effective fiber to meet the rumen function demands of the cow.

Whole plant corn silage should be chopped at 3/8-1/2 inch TLC. Longer chop can create difficulties in packing and unloading. It also results in kernels passing into the manure and preferential sorting by cows at the bunk. Recently, however, many producers are using kernel processors on corn silage. With the use of these devices, corn silage can be effectively chopped at 3/4-1 inch TLC and still be adequately packed in bunker silos.

Haylage should be chopped at 3/8 inch TLC to provide more than 15-20% of forage particles at greater than 1 1/2 inches long. Chopping haylage at greater lengths to improve effective fiber in the diet is a common practice currently employed by many producers. Haylage tends to stratify in bunkers and longer chop makes it more difficult to unload. Digging out long cut haylage allows for deeper air penetration into the silage mass, which can lead to poor aerobic stability and higher dry matter losses. A reasonable compromise may be to shorten the TLC in haylage and use longer cut processed corn silage for effective fiber in the diet.

It has been shown that acid detergent fiber (ADF) is as much as four percentage units higher in coarse cut haylage compared to fine cut haylage. The higher ADF results in a lower predicted energy density. It would take the addition of more than 460 bushels of corn for each 1000 tons of haylage to give coarse cut material the same energy density as finer cut material (Ruppel et al., 1995).

FILLING AND PACKING THE SILO

The silo should be filled as quickly as possible within the limitations of harvest and packing equipment. Adequate packing is one of the most critical operations in the filling of a bunker silo. Insufficient packing allows for the trapping of oxygen, which can increase dry matter loss due to extended plant respiration. Poor pack subsequently allows more oxygen penetration into the silage mass when feedout begins, which also leads to decreased aerobic stability. The operator must match the packing effort to filling speed. Packing at a minimum rate of 800 to 1000 hour-pounds/ton has been shown to result in better aerobic stability (Ruppel et al., 1995) Use the following formulas (Ruppel, 1997) to determine filling rate:

Filling Rate (tons per hour) = Packing Vehicle(s) Weight ¸ 800

To calculate the additional packing weight needed for fast filling days, use the following formula:

Packing Vehicle(s) Weight = Filling Rate (tons per Hour) x 800

More tractors, heavier tractors, wheeled dozers, and enlarged blades or plows are being used to increase packing capacity on many farms today (Ruppel, 1997). Packing technique is also important. Spreading out incoming loads as soon as possible and attempting to have less than 6 inches of silage under the packing wheels helps transfer the weight of tractors into silage compression. This insures rapid and complete removal of oxygen.

Packing is important, but use caution when packing very wet immature crops, especially alfalfa haylage. Over packing of this material can squeeze water from tender plant cells and rupture them. This water can create effluent which robs the silage of valuable soluble nutrients. Over packing can also allow water to collect along the different strata of the silage mass creating streaks of very wet silage. If the moisture is greater than 70% in these streaks, a clostridial fermentation may be initiated, which can dramatically reduce the quality of silage in these areas. When packing this type of material 800 hour-pounds/ton should be sufficient (Kautz, 1997).

Filling method is also important in maximizing dry matter recovery and energy content. Placing Fresh cut forage packed into bunkers at a 30 degree angle is known as a progressive wedge and is the most efficient way to fill a bunker. Horizontal layering of forage or dumping off the load at nearly full height results in higher ADF and lower non-structural carbohydrate levels in the ensiled material (Ruppel, 1997).

Keeping the fresh forage in a slightly concave configuration can also increase packing efficiency. ( Figure 1.) Keeping the material in this shape until the top of the wall is reached will help direct the weight of the packing vehicle toward the outside walls of the silo. This can result in better packing density and less shrink along the walls.

Packing Tractor Pressure

Silage Mass

Figure 1.

One other important point to remember when sizing, filling and packing silos is to build the structure big enough so that silage does not reach above the tops of the walls. Rounding off the material just at the top of the wall to about 2-4 feet above the wall in the center provides an adequate slope for rain to run off but still allows safe and efficient packing.

COVERING THE SILO

The final step in managing a bunker silo is to cover the silage mass to prevent exposure to oxygen, sunlight, rain and snow during storage. The value of covering is an often discussed topic, but the data conclusively shows the value of a cover. Many ideas have surfaced as to what cover is best. Currently 4-6 mil black or black/white sandwich plastic is the best option. This plastic should be secured with tires (preferably split) placed edge to edge on top of the plastic.

Research data has shown that silage (either haylage or corn silage) will lose an AVERAGE of 30% of its dry matter when stored in an uncovered bunker silo. Most of the losses are highly valuable nutrients such as non-structural carbohydrates and soluble protein. This would put the value of the material lost at about $100 per ton of dry matter! Leaving a bunker silo uncovered is equivalent to using 30% of the top three feet of silage as your silo cover and this can be incredibly expensive. Table 2 (Ruppel, 1997) compares silo cover costs for plastic and silage covered bunker silos. A silage cover is nearly 20 times more costly than even the more expensive plastic silo cover.

Table 2. Comparison of plastic and silage silo covers costs for a 9’ x 40’ x 100’ bunker silo

Silo Cover Material	Cost per Square Foot ($)	Cost per Ton, As Fed ($)	Cost for Silo ($)
Black, 6-mil Plastic	0.023	0.11	92
Black and White, 6-mil Plastic	0.034	0.16	136
Silage¹(valued at $30/ton	0.653	2.99	2,612
Silage¹ (valued at $100/ton	2.175	9.97	8,700

_____________________________________________________________________________

¹ Based on 30% more silage dry matter lost in top three feet when bunker silos are not covered

compared to bunker silos covered with plastic (Bolsen et al., 1993)

The cover on a bunker silo, in addition to being topped with tires, can further be secured at the edges with sandbags. Experience has shown that folding the plastic back on itself (about 18 inches of overlap) and then laying sandbags next to the edge of the wall helps keep moisture from running down the outside edge of the silage mass. Do not place the sandbags on the top of the wall. This will lead to increased spoilage as the silage shrinks away from the cover (Kautz, 1997). Bunker covers that are not adequately secured may be worse than no cover at all. A flapping bunker cover acts as a conduit to pump more air along the surface of the ensiled material and can increase the depth of the top spoilage.

Feedout Management

After spending considerable time and money to get quality forage into a bunker silo it only makes sense to manage the silage carefully during feedout. It has been well documented that over 50% of dry matter losses occur during storage and feedout. These losses begin when the bunker is opened and the face is exposed to oxygen. Careful face management can significantly reduce these losses.

Plan to feed a minimum of six inches from the entire face every day if possible. Table 3 shows how high losses can be if the silage is poorly packed and the face is exposed to oxygen for several days. When removing silage from the face of the bunker, it is important to carefully shave or chip the material working from bottom to top. (Figure 2) Keep the face as clean and straight as possible. As previously mentioned, design the silo so unloading equipment can reach the top of the face. Digging or gouging the face will cause fractures which will allow air penetration into the silage mass reducing aerobic stability. Only remove enough material for one day’s feeding at a time. Leaving loose material at the base of the face will lead to heating and substantial additional dry matter losses.

Silage Inoculants

Use of a quality, research proven bacterial silage inoculant is a very important part of bunker silage management. Table 1 shows that the average storage and feedout dry matter loss in bunkers is 12-16%. These losses can be reduced by 1/3 to 1/2 with the use of an inoculant. Inoculants have also been shown to improve nutrient utilization, protein quality and aerobic stability. A dollar per ton investment in an inoculant for bunker silage can be expected to return a minimum of 3-5 dollars per treated ton.

Ruppel, 1997.

Setting up a monitoring program for the silage operation can improve profitability. Keeping track of progress with various parameters will help identify problem areas and help fine tune the operation (Ruppel, 1997).

1. Feed Bunk Life - Take silage samples and place into a Styrofoam container. Monitor the temperature rise over time. This can help determine which silages under which conditions contribute most to poor aerobic stability.

2. Particle Size Separator - Several kinds are available. The Penn State model is currently the most popular. These devices can help determine which silages are chopped too fine and which ones could be chopped finer. They can also be used to monitor effective fiber levels in the TMR.

3. Packing - This is the most important part of making silages in bunkers and is often neglected. Know the weight of packing tractors and monitor the rate at which silage is delivered to the bunker.

4. Feedout Rate - Make a line on the bunker wall every week or two to determine how fast silage is being removed from the silo.

5. Unloading Technique - Develop a scoring system and rate the operators and face quality on a regular basis

6. Forage Quality Changes - Take composite samples of fresh material entering the silo and compare with silage samples during feedout. Develop standards for silages. Look at percentage of ADF and NDF increases, NE_L and NSC decreases and changes in protein fractions.

7. Video - There is an excellent video available from the Northeast Regional Agricultural Extension Service entitled “Bunker Silo Management” (Pitt et al., 1995). It was designed to help employees visualize better ensiling practices in real farm situations.

Respiration

Harvesting

Alberta Agriculture. Silage Manual, Alberta Agriculture Publ. No. AGDEX 120/52-2, Edmonton, Canada, 1988.

Bolsen, K.K., J.T. Dickerson, B.E. Brent, R.N. Sonon, Jr., B.S. Dalke, C. Lin and J.E. Boyer, Jr. “Rate and Extent of Top Spoilage Losses in Horizontal Silos.” J Dairy Sci 76: 2940-2962, 1993.

Bolsen, K. K. “Issues of Top Spoilage Losses in Horizontal Silos.” Proceeding from Silage: Field to Feedbunk, NRAES-99, 1997.

Holter, J.B. “Aspects of storing and sampling ensiled forages.” J Dairy Sci 66: 1403-1408, 1983.

Kautz, W.P. “Evaluating Silage Quality.” Proceedings: Four State Nutrition Conference, Lacrosse WI., 1997.

Mahanna, W.C. “Troubleshooting Silage Problems with ‘Seed to Feed’ Considerations.” Proceedings from Silage: Field to Feedbunk, NRAES-99, 1997.

Pitt R.E., K.A. Ruppel and L.E. Chase. Bunker Silo Management, Cornell University Media Services, 1995.

Ruppel, K.A. “Economics of Silage Management Practices: What Can I Do to Improve the Bottom Line of My Ensiling Business?” Proceedings from Silage: Field to Feedbunk, NRAES-99, 1997.

Ruppel, K.A., R.E. Pitt, L.E. Chase and D.M. Galton. “Bunker Silo Management and Its Relationship to Forage Preservation on Dairy Farms.” J Dairy Sci 78: 141-153, 1995.