Many producers are searching for improved methods of covering bunker silos and silage piles to reduce spoilage. A demonstration was prepared for Wisconsin Farm Progress Days to show a side-by-side comparison of some surface covering alternatives that producers have tried.
Six clear plastic cylinders, 8-in. diameter by 4-ft tall, were filled with wilted, chopped alfalfa on June 3, 1997. Characteristics of the alfalfa are listed in Table 2 in the row labeled "Day 1." This was an early-cut, high-quality forage. Alfalfa was packed in the cylinders to a density of about 40 lb/cu ft (wet weight). Each cylinder received a different covering treatment. Clear polyethylene plastic was held on the top of one cylinder with a hose clamp. Other cylinders were covered with 5 in. barn lime, 5 in. sawdust, and 0.5 in. molasses. Oat seed was sown on another cylinder. (The oats did not germinate.) The last cylinder received no cover. The sides of each cylinder were wrapped in fiberglass insulation to conserve heat during fermentation.
The cylinders were stored outside until July 21, 1997, when they were moved to the site of Farm Progress Days for exhibition of the results. When the cylinders were returned to Madison, they were stored indoors. On September 22 (112 days after filling), the silage was removed for analysis. Throughout the storage period, 0.5 in. water was applied to the top of the silage at the end of each week for which rainfall was less than 0.5 in.
The results of measurements on the silage are presented in Tables 1 and 2. From Table 1, it is apparent that little depth change occurred when the silage was covered with plastic, while significant depth change occurred for the oat seed, molasses, and no cover treatments. Mold was observed in the top 3 to 5 in. for the plastic- and lime-covered cylinders, and much more mold was observed for the other treatments. For all covers except the plastic, 7 to 25.5 in. of material were lost due to settling or mold removal. Dry matter losses are recorded in the last column of Table 1. These losses include moldy silage removed to achieve quality feed.
The plastic and lime covers did an admirable job of controlling spoilage. There was a slightly larger depth of mold with the lime. Field observations of full-sized silos indicate areas of shrinking and cracking in lime layers, which makes silage below the cracks vulnerable to significant spoilage. Therefore, these demonstration results might be difficult to duplicate on a large scale. Dry matter losses exceeded 15% for the other treatments and were excessive compared to the losses for the plastic cover.
|
Cover Treatment |
(in.) |
(in.) |
(in.) |
(in.) |
|
Plastic |
0.75 |
3.25 |
4.0 |
9.20 |
|
Lime |
2.75 |
4.50 |
7.25 |
10.20 |
|
Sawdust |
3.25 |
7.50 |
11.0 |
18.96 |
|
Oat Seed |
6.50 |
12.15 |
18.75 |
19.01 |
|
Molasses |
6.50 |
12.50 |
19.00 |
15.95 |
|
Uncovered |
7.50 |
18.00 |
25.50 |
29.92 |
|
Cover Treatment |
|
|
|
|
|
|
Day 1 |
|
67.1 |
6.2 |
27.9 |
22.0 |
|
Day 112 |
|
|
|
|
|
|
Plastic |
top |
69.7 |
4.3 |
26.4 |
24.5 |
|
|
middle |
68.4 |
4.3 |
27.2 |
24.3 |
|
|
bottom |
68.2 |
4.4 |
27.2 |
23.6 |
|
Lime |
top |
73.9 |
4.5 |
26.2 |
26.8 |
|
|
middle |
68.5 |
4.4 |
28.2 |
23.0 |
|
|
bottom |
69.0 |
4.4 |
28.9 |
21.2 |
|
Sawdust |
top |
83.6 |
4.8 |
24.8 |
32.6 |
|
|
middle |
73.4 |
4.3 |
27.5 |
23.3 |
|
|
bottom |
70.2 |
4.3 |
27.9 |
22.9 |
|
Oat Seed |
top |
85.0 |
5.1 |
22.2 |
37.2 |
|
|
middle |
77.1 |
4.5 |
28.2 |
25.7 |
|
|
bottom |
73.2 |
4.3 |
30.6 |
19.8 |
|
Molasses |
top |
83.6 |
5.1 |
23.8 |
35.8 |
|
|
middle |
74.4 |
4.3 |
27.9 |
23.1 |
|
|
bottom |
72.8 |
4.2 |
30.4 |
19.3 |
|
Uncovered |
top |
84.8 |
6.1 |
24.9 |
34.9 |
|
|
middle |
81.7 |
5.5 |
22.5 |
32.2 |
|
|
bottom |
73.3 |
4.3 |
28.7 |
22.5 |
Table 2 indicates a fairly uniform moisture increase of about 1 to 3 percentage points in the silage with the plastic cover. The moisture increase is probably due to a small amount of dry matter loss during fermenation and due to water released during aerobic decomposition. In the other cylinders, the final moisture content is appreciably higher and generally shows a gradient with higher moisture at the top of the cylinder. This moisture comes from actual and simulated precipitation as well as from increased deterioration of the silage.
For good silage preservation and extended feed bunk life, a pH below 4.5 is desirable. The sawdust, oat seed, molasses, and uncovered treatments had silage at the top that had a pH greater than this value.
Crude protein values stayed the same or increased slightly where good fermentation was achieved, but protein levels decreased where top spoilage was significant. The acid detergent fiber values showed an opposite trend. Both of these trends suggest that soluble nutrients might have been flushed down in the cylinders due to water movement.
The results of this demonstration confirm the value of tightly sealed plastic as the preferred method of excluding oxygen and precipitation to preserve silage stored in bunker silos and piles.
The author would like to thank Dr. Richard Muck and his staff at the U.S. Dairy Forage Research Center and Dr. Randy Shaver (Dairy Science Department, University of Wisconsin-Madison) for their assistance, and Wisconsin Farm Progress Days, Inc. for their financial support. The author would also like to thank Dr. Keith Bolsen (Kansas State University) for inspiring this demonstration.
This page is part of the Biosystems and Agricultural Engineering Department web at http://www.bae.umn.edu/