3 steps to estimate forage weight

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Most dairy producers don't have a drive-over scale to weigh forages harvested from their fields. However, in certain situations, it's handy to know the weight of the alfalfa haylage or corn silage in your wagons as they come from the field, says Daniel Wiersma, assistant station manager at the University of Wisconsin's Agricultural Research Station in Marshfield, Wis., and Brian Holmes, extension agricultural engineer at the University of Wisconsin-Madison.

To help you estimate the weight of freshly chopped forage in a wagon, Wiersma and Holmes suggest following a three-step process:


Step 1. Calculate forage volume

First, measure each chopper box or wagon to determine its length, width and estimated fill height. Be sure to record these measurements and keep them for future reference. In this example, the forage wagon measures 8 feet wide, 16 feet long, and has an average height, or fill depth, of 6 feet. Using these measurements, calculate the volume of forage in the wagon:

8 feet wide
x 16 feet long
x 6 feet high
= 768 cubic feet


Step 2. Calculate forage dry weight

Next, determine the dry weight of the forage in the wagon. To do so, multiply the forage volume calculated in Step 1 by the average forage density, which, in our example, happens to be 5 pounds of dry matter per cubic foot. (See related article, "Study calculates average forage density on page 63.")

5 pounds dry matter per cubic foot
x 768 cubic feet
= 3,840 pounds dry forage

Next, divide the pounds of dry forage by 2,000 pounds to arrive at tons of dry forage in the wagon:

3,840 pounds dry forage
÷ 2,000 pounds per ton
= 1.9 tons dry forage


Step 3. Calculate the wet weight of the forage

To determine the wet weight of forage in the wagon, divide the pounds of forage dry matter from Step 2 by the average
forage dry matter percent which, in this example, happens to be 40 percent.

3,840 pounds dry forage
÷ 0.4 percent dry matter
= 9,600 pounds wet forage

To determine the wet forage weight in tons, divide the pounds of wet forage by 2,000 pounds per ton:

9,600 pounds wet forage
÷ 2,000 pounds per ton
= 4.8 tons wet forage

"This procedure is useful for on-the-farm inventory management," Holmes says. However, if you plan to sell forage directly from the field, weigh each load on a drive-over scale for better accuracy.

If you'd like to learn more about using this quick method to estimate the weight of forage in a wagon, check out Wiersma's and Holmes' fact sheet at the following Web site: www.uwex.edu/ces/crops/uwforage/storage.htm
 



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