Joe Lawrence, Cornell University PRO-DAIRY
Ron Kuck, Cornell Cooperative Extension of Jefferson County
As harvest season approaches it is a good time to make sure everything is in order to make the season as successful as possible. There are lots of rules and sayings regarding quantity; “too much of a good thing”, point of diminishing return, optimum range and the list goes on. Often times in crop production we pay close attention to these rules. We have very good data to show the point of diminishing return on fertilizer applications, seeding rates, forage quality versus yield, etc.
In other cases there are guidelines that offer a minimum value or goal to shot for but there has yet to be proven that there is a point of diminishing return and sometimes these minimum guidelines give us a false sense of accomplishment. There are a few examples of this relative to forage harvest.
Here we will address bunk silo density, while this is not new information it remains an opportunity for many. Based on research conducted by Curt Ruppel at Cornell in the mid 1990’s the benchmark was set that the minimum density for silage should be 14 lbs dry matter (DM)/ cubic foot. At some point in time the word minimum seemed to be lost from this and many began to think about 14 lbs as their goal not just the minimum. As a guideline for achieving this density the rule of thumb of 800 lbs of packing weight per ton of forage per hour was developed, again as a minimum.
In reality we have yet to see a bunk packed too much or any negative outcomes from extra resources committed to packing during silo fill. Silo filling is a very dynamic process and parameters can change from hour to hour. If you set your goal for the minimum of 14 and your assumptions for filling are not accurate the risk of ending up with a density lower than 14 becomes high.
Investing in “packing power” to get the highest density possible assures that even when things are not going exactly as planed you have a better chance of keeping the density at 14 lbs or above. A higher density will improve forage quality, reduce dry matter losses and increase the efficiency of your storage footprint.
The calculations can be done for various storage strategies; bunks with wall, drive over piles, etc. A simple example would be a modest size bunk that is 40’wide by 100’ long with 10’ sidewalls. This provides 40,000 cubic feet. With a density of 14 lbs DM per cubic feet that would result in a storage capacity of 280 tons of DM and expected DM losses (shrink) of approximately 16.8% (Ruppel, 1992).
Now let’s take that same storage space and increase the density by 4 lbs DM to 18 lbs DM per cubic foot. This increases the capacity of your bunk to 360 tons DM, an increase of 80 tons DM or approximately 36%. Additionally, DM losses would be expected to drop by 3.4% to approximately 13.4% (Ruppel, 1992).
Increasing the capacity of your current storage by this amount could eliminate the need for investing capital into more storage space and also reduce the necessity to pile forage above the walls in the case of bunk silos. Staying with the walls alone can drastically cut down on spoilage and improve safety around the feed storage.