This time of year, many producers are feeding cows hay. Have you ever stopped to think about what the nutrients in the hay are worth as fertilizer once they have been processed by the cow?
Mature cows at maintenance should excrete 100 percent of the nutrients they consume in terms of nitrogen, phosphorus and potassium.
For example, 100 cows are being fed 30 pounds per head per day of 17 percent protein alfalfa hay that is 0.3 percent phosphorus and 2.4 percent 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?
3,000 lbs. of alfalfa hay X 0.17 crude protein = 510 lbs. of protein. Nitrogen X 6.25 = crude protein. Taking 510 lbs. of crude protein and dividing by 6.25 = 81.6 lbs. of nitrogen in the fed hay. Only about 35 percent of the nitrogen in manure and urine is available to be used. The balance is lost to volatilization as ammonia.
Using 81.6 lbs. of nitrogen X 0.35 = 28.6 lbs. of nitrogen available to be used by growing plants from the fed alfalfa hay.
The availability for phosphorus and potassium in manure and urine from feed consumed is 100 percent.
To find the value of phosphorus and potassium in the fed alfalfa, take 3,000 lbs. X 0.003 = 9 lbs. of phosphorus and 3,000 lbs. X 0.024 = 72 lbs. of potassium.
In one ton of alfalfa hay, there are approximately 19 lbs. of nitrogen, 6 lbs. of phosphorus, 48 lbs. of potassium and 6 lbs. of sulfur that are applied to the ground in excreted manure where the hay is fed. The fertilizer nutrient value of these minerals at current market prices is $1/lb. of nitrogen ($19), $0.95/lb. of phosphorus ($5.70), $0.65/lb. of potassium ($31.20) and $0.75/lb. of sulfur ($3.75), which would in total equal $59.65 per ton! This value doesn’t include other micronutrients and the organic matter in manure and wasted hay.
It is common to see weed problems develop on rangelands 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?
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. — Aaron Berger, Nebraska Extension beef educator
