Economics of sealing horizontal silos

Determining the value of silage saved by effectively sealing a horizontal silo requires only a few simple calculations, but it is still a concept that is often overlooked by many livestock producers who store large amounts of silage in that manner. Kansas produces about 3.0 million tons of silage annually, primarily from corn and sorghum. A majority of this silage is made and stored in either bunker, trench, or "drive-over" pile silos . Only 20 to 30% of these silos are sealed after filling. Producers who do not seal need to take a second look at the economics of this highly troublesome "technology" before they reject it as unnecessary and uneconomical. The loss from a 100 x 250 ft silo filled with corn silage can exceed $10,000.


Introduction
Three economically attractive methods in Kansas for storing large amounts of ensiled forage are the horizontal silos (i.e., bunker, trench, or pile), but because so much of the surface of the ensiled material is exposed, dry matter (DM) and nutrient losses can be extensive .If left unprotected, losses in the top 2 to 4 ft can exceed 50%.This is particularly disturbing when one consid e rs that in the typical horizontal silo, over 20% of the silage might be within the top 4 feet.
These losses can be minimized by sealing (covering ) the ensiled mass with polyethylene sheets, which usually are weighted with tires or soil.Although this method minimizes losses, it is so awkward, cumb e rsome, and labor intensive that many producers feel the silage saved is not worth their time and effort.
Top-spoilag e research ha s been conducted at Kansas State University since 1989, and the results d ocument the magnitude of the DM and nutrient losses in the original top 3 ft of the ensiled crop.However, these losses can not be seen until the silo is opened.Even then, the spoilag e might be apparen t only in the top 6 to 12 inches of silage, obscuring the fact that this area of spoiled silage represents substantially more silage as originally stored.
We provide here a few simple equations, that can be hand-calc ulated or incorporated into a computer spreadsheet.They allow producers to estim ate the value of silage saved by sealing, based on their crop value, silo dimensions, cost of the sealing material, and labor to cover their silage.

Calculations and Examples
Calculating the value of silage saved by sealing is based on four economic inputs and two silo/silage inputs.The four economic inputs are: 3) Cost of the weighting material (zero was used in the examples) 4) labor cost ($/hr × number of hrs).
Ten hours per 4,000 ft of polyethylene 2 sheet were used to calculate the labor cost.
In order to accoun t for overlapping from sheet to sheet and along the side walls or base, we assumed a covering efficiency of 80%.
The first of the two silo/silage inputs determine s the amount of silage within the origina l top 3 ft of the silo after filling is complete .It is determined by multiplying the silo width(ft) by length(ft) by depth of interest (3 ft) by the silage density (lb/f t) and dividing 3 the product by 2,000 (lb/ton).
The second silo/silage input estimates the amount of silage within the original top 3 ft of the silo that is lost as spoilage.These values (50% of sealed , 20% if unsealed) are based on researc h conducted at Kansas State University and published in KAES Reports of Progress 623, p. 70; 651, p. 127; and 727, p. 59 and 63.
The following example estimates the net return from sealin g a horizontal silo 40 ft wide by 100 ft long (4,000 f t). 2 The concepts sh own above are presented in a user-friendly spreadsheet format in Table 1.The first nine lines are economic inputs determined by the producer, and the next six lines are results that are based on formulas utilizing the producer's inputs.They can be programme d easily into the spreadsheet using the row letters as guides.
The most important single facto r influencing preservation efficiency of ensiled forages is the degree of anaerobic fermentation achieved durin g ensiling.When silage is not sealed or when the seal is inadequate, air and moisture enter the mass and affect both the ensiling process and silage quality durin g the storage and feedo ut phases.Based on the examples in Table 1, sealing a 40 ft × 100 ft silo could save approximatel y $1,600 worth of silage.Using the same concept, covering a 10 0 ft × 400 ft silo could save the producer over $16,000.
Although future technolo gy might introduce a more environmentally and user-friendly product , polyethylene (6 mm) is the most effectiv e sealing material available today .The most common sealing method is to place the polyethylen e sheet over the ensiled forage and weight it down with rubber tires (20 to 25 tires per 100 sq ft).
Research-base d calculations confirm that the financial loss incurred b y not sealing silage is substantial and reinforces our recommendation that sealing the exposed surface of a horiz ontal silo is one of the most important management decisions in any silage program.