How Much Does That Bale Really Weigh? Feeding and Fertilizer Implications

Accurate estimation of bale weights can assist livestock producers with winter feed inventory and provide yield data per acre, which can be used for efficient nutrient application.

Winter Feeding

Most livestock producers estimate hay bale weights when they plan for their winter feeding needs. However, many producers grossly overestimate the weight of those bales. This can cause them to run short of hay for the winter, leaving them scrambling to find more in late winter.

All producers know that bale weights can vary greatly depending on the bale's size and how tightly the baler packed the hay into the bale. To better estimate the weights of both round and square bales, Dennis Hancock, from the U.S. Dairy Forage Research Center in Madison, Wisconsin, developed some recommendations.

The recommendations allow producers to make estimates based on bale density per cubic foot. To calculate the cubic feet of a square bale, multiply the width by the length by the height of the bale. To calculate the cubic feet of a round bale, take half the diameter of the bale and square that. Then, multiply that number by 3.14 and then the bale width. For example, a 4-foot by 5-foot bale is 4 feet wide and 4 feet in diameter. Therefore, the cubic feet of this bale would be 2.5 x 2.5  x 3.14 x 4, which is 78.5 cubic feet.

Start by estimating bale density per cubic foot by pressing on the bale. Hancock uses the following estimates: If the bale feels loose and you can easily press into the forage without it springing back, the bale probably contains around 9 pounds of dry matter per cubic foot. Bales that still give when you press on them, but feel a bit firmer than the really loose bale, likely contain around 10 pounds of dry matter per cubic foot. If the bale feels fairly tight but dents under pressure, use 11 pounds of dry matter per cubic foot. For those bales that are really tight and would be difficult to insert the bale spear into, figure on 12 pounds of dry matter per cubic foot. This calculation method is applicable to small square bales, large square bales, and round bales.

So, if the 78.5 cubic foot bale was baled really loosely, it would only weigh around 706.5 pounds. A slightly tighter bale would weigh 785 pounds. The tight bale would weigh 863.5 pounds, and the really tight bale would weigh 942 lbs. Now, how will that measure up for winter feeding purposes?

Most beef cows require around 30 pounds of hay per day through the winter months. For a herd with 25 cows and a winter feeding period of 150 days, this herd would require approximately 112,500 lbs. of hay. If the beef producer has loose bales, he would need around 159 bales for the winter. However, if he has really tightly-made bales, he would only need 120 bales.

We can also consider the average sheep flock or goat herd of 25 females. If they require an average of 5 pounds of hay per day, then the flock or herd would require 18,750 pounds of forage for the 150-day feeding period. This translates into 27 loosely made bales versus 20 really tightly made bales. 

Fertilizer and Manure Needs

Coupling known bale weights with the number of bales harvested annually from a field can be used to estimate the total tons of forage removed on a per-acre basis. For example, if 50 of the 942-pound round bales from above were harvested over the summer from a 10-acre field, the total field yield would be 50 bales X 942 pounds/bale =  47,100 pounds of hay per season. Dividing this by the 10 acres and 2,000 pounds in a ton shows that about 2.4 tons of hay were removed per acre. So, how much fertilization is needed for this yield?

The Penn State Agronomy fertilization recommendations for nitrogen, phosphorus (P₂O₅), and potassium (K₂O) for grass hay are 50-15-50 per ton of hay harvested per acre. In our example, these numbers can be multiplied by 2.4 tons of hay yield to provide a recommendation of 120-36-120 pounds of N-P-K per acre. Applying more nutrients than this may not provide agronomic or economic benefit. These nutrients can be applied in the form of commercial fertilizer, manure, or a combination of these sources.

Determining manure application rates can be tricky because only a fraction of the N in manure will be available to the crop. Again, the Agronomy Guide provides some insight into N availability factors. In turn, these factors are incorporated into the calculations found in the state’s Manure Management Manual and Nutrient Balance Sheet Excel planning tool. Both of these can be used to determine manure application rates. A good starting point for exploring how to determine your manure application rates is at the Penn State Nutrient Management Education Program website. The site features a Help Center link that connects you with experts when you need assistance.

The moral of this story is that feed planning begins with understanding how much your hay bales weigh. And, if you buy hay by the bale, this can mean a big difference in the feed cost for the winter!