This past winter, during fertilizer recertification, I combined a couple of Dr. Emma Matcham’s presentations to create a fertilizer training for both livestock and grain producers.
Matcham is an assistant professor at Ohio State University who focuses on Integrated Forage Systems. Fertilizer recertification is the program I geek out on because I can convert much of the material into numbers, and I am a very number-minded person! If you like numbers, you’ll love this article; if not, I apologize in advance!
First, let’s talk about the “give” livestock provide to the soil. A study from the University of Minnesota Extension recorded thousands of samples of liquid and solid manure from swine, poultry, beef and dairy to determine the nutrient contents for pounds/ton or pounds/1,000 gallons. Below are the results from the research:
Liquid (pounds per 1,000 gallons)
• Swine: 42 pounds Nitrogen (N), 22 pounds Phosphorus (P) and 30 pounds Potassium (K)
• Beef: 40 pounds N, 20 pounds P and 27 pounds K
• Dairy: 20 pounds N, 10 pounds P and 22 pounds K
Solid (pounds per ton)
• Beef: 19 pounds N, 10 pounds P and 18 pounds K
• Dairy: 16 pounds N, 8 pounds P and 18 pounds K
• Poultry: 52 pounds N, 47 pounds P and 38 pounds K
Research shows that when livestock are grazing pastures, they return roughly 70 to 90% of the nutrients back to the pasture. However, nutrients are typically not distributed evenly across the pasture and are typically higher near shade or water sources. Research has shown that more intensive grazing systems provide a more even distribution of nutrients due to the smaller pasture. However, these systems require more labor and may not be an option for all producers.
This is the example that Matcham explained in her presentation. Let’s say we have a 750-pound heifer in the pasture. Let’s assume the heifer will eat 2.5% of its body weight in forages per day on a dry matter basis. That means that the heifer will consume about 18.75 lbs. of dry matter a day, but for the sake of simple math, let’s call this 20 pounds a day. Over a 30-day period, this heifer will consume 600 pounds (20 pounds x 30 days) of dry matter.
We also know that for each ton (2,000 pounds) of forage removed, it removes 12 pounds P and 49 pounds K. So, from grazing this heifer for thirty days, it is consuming 3.6 pounds of P and 14.7 pounds of K from the soil.
Since we are grazing this pasture, this heifer is going to give us back between 70 to 90% of the nutrients removed in the form of manure. For this example, let’s call it 80%. That means, when grazing this pasture for thirty days, that heifer gives us back 2.88 pounds P and 11.76 pounds K. Now let’s subtract the “give” and “take” from the heifer. In thirty days, this one heifer will remove roughly 1 pound P and 3 pounds K from the soil.
This method allows us to understand how much nutrients our livestock are removing from the soil to help manage our fertilization needs. We can use this calculation with multiple head of cattle to estimate how much nutrients we need to replenish from grazing a pasture. This can be done multiple years, but it is always highly encouraged to take a soil sample every three years to ensure proper soil fertilization.
(Josh Winters is the Jackson County Agriculture and Natural Resource Extension Educator. He can be reached at winters.249@osu.edu.)
