Mr. Tom Noyes, Dairy Extension Agent, Wayne County
With milk prices at record lows, dairy producers look for ways to cut costs and one possibility would be not applying fertilizer to pastures and other forages. Is this a wise decision? Well, that depends. What are the soil fertility levels, what forage productivity do you want, and are there legumes in the stand?
The OSU Extension fact sheet on "Fertility Management of Meadows" provides excellent recommendations for fertilizing pastures and forage crops. It doesn't matter how the forage is harvested (grazed or mechanical), it will remove from the soil the three major nutrients: nitrogen (N), phosphorous (P), and potassium (K). The amount removed depends on the yields. For each ton of tall grass or legume forage, it will remove 13 lb of phosphate (P2O5) and 50 lb of potash (K2O). These nutrients can come from soil reserves, through commercial fertilizers, manure, or livestock nutrient cycling (grazing livestock).
Let's first address the soil levels of these nutrients. Nitrogen soil reserves are relatively low so N needs to be applied or derived from legumes. For good yields of forage, soil P levels need to be maintained at 15 to 25 ppm (30 to 50 lb/acre). Potassium soil levels should be 125 to 200 ppm (250 to 400 lb/acre). On many livestock farms that have regularly applied manure, the levels of P and K may have increased to levels where a year of no commercial fertilizer application will not affect crop yields. Soil P levels of over 35 ppm and K levels of over 200 ppm can provide normal forage yields from soil nutrient reserves, especially for pastures where considerable nutrients are being recycled by the grazing livestock without additional fertilizer.
For N, it is a different story. Applying N and how much to apply will be determined by the legume content of the forage stand. The OSU fertilizer recommendations omit applications of N when the forage content is made up of 35 to 40% or more legumes. When the stand is less than 20% legumes, consider it a grass stand and apply N. Applying small amounts of N to pastures with 20 to 25% legume will increase forage quality and yields.
When grass is the predominant forage species, N fertilization is extremely important. Economic returns have been demonstrated when a total of 150 to 175 lb/acre/year of N are split applied, three times during the growing season. By the time you read this article, the spring application times will have passed, so there will be an opportunity for two more applications.
An application towards the end of June, timed with a potential ½ inch rain, would pay dividends in reducing mid-summer slump. Apply 35 to 40 lb/acre of actual N with a stable N source like diammonium phosphate (DAP) or ammonium sulfate.
For extended grazing in the fall, an application of 30 to 50 lb/acre of N in late August will give you a flush of grass much like spring, which will provide increased forage quality and yields well into the late fall months.