Have you ever stopped to think about what the dollar value of the nutrients in the hay are worth as fertilizer once they have been processed by the cow? Here’s some math to provide an answer:
Mature cows at maintenance should excrete 100% of the nutrients they consume in terms of nitrogen, phosphorus and potassium.
For our example, let’s use 100 cows being fed 30 lbs. per head per day of 17% protein alfalfa hay. The hay is .3% phosphorus and 2.4% potassium on an as fed basis. What is the value of the nutrients available to the pasture or field where the manure is being deposited?
3000 lbs. of alfalfa hay X .17 crude protein = 510 lbs. of protein.
Nitrogen X 6.25 = crude protein.
So, we take 510 pounds of crude protein and divide it by 6.25
510 ÷ 6.25 = 81.6 pounds of nitrogen in the fed hay.
Now, only about 35% of the nitrogen in manure and urine is available to be used. The balance is lost to volatilization as ammonia. Here’s the formula to figure how much nitrogen is available to be used by growing plants from the fed alfalfa hay.
81.6 pounds of nitrogen X .35 = 28.6 pounds of nitrogen available
The availability for phosphorus and potassium in manure and urine from feed consumed is 100%. The forumula for finding the value of phosphorus and potassium in the fed alfalfa:
3000 lbs. X .003 = 9 lbs. of phosphorus
3000 lbs. x .024 = 72 lbs. of potassium.
How Much Is That Worth?
Here’s the approximate amount and value of nutrients applied to the ground in one ton of manure from fed alfalfa hay:
Nutrients in hay have value. Finding ways to effectively utilize and recycle nutrients is economically beneficial. Strategically thinking about how to capture the value of nutrients in harvested forage is one way to reduce fertilizer prices for growing crops.
For more information on calculating the nutrient value of harvested feeds, visit this University of Missouri Extension article titled “Calculating Fertilizer Value of Supplemental Feed for Cattle on Pasture”.
P.S. Worried About Weeds?
It is common to see weed problems develop on rangeland that cattle are fed on during the winter months. The nutrients from the hay are often concentrated in feed areas and the availability of nitrogen, in particular, in rangeland situations encourages weed growth. If hay is being fed, is there an opportunity to feed cattle on ground where the nutrients can be utilized for growing tame perennial or annual forages that would respond to the fertilizer?
And…too many nutrients can also be a problem.
In this 6-part series, Jim Gerrish takes us through nutrients in hay, how to feed to get the most out of them, and how to prevent too many nutrients (like nitrogen and phosphorus) from causing problems for our ponds, lakes, streams and rivers.