By Greg LaBarge, CCA, Ohio State University Extension agronomist
Balanced fertilizers with equal percentages of nitrogen, phosphorus, and potassium like 19-19-19 and 12-12-12 can be useful but should never be the long-term, sole fertilizer source applied to a forage field. Why? You can find the answer by comparing crop nutrient removal to nutrient application.
First, let’s estimate crop removal. A cool-season grass hay mix yielding 3 tons per acre will remove 36 pounds of P2O5and 144 pounds of K2O. The removal values come from Nutrient Removal for Field Crops fact sheet (ohioline.osu.edu/factsheet/anr-96). The reference also lists other forage crops.
Now let’s determine the nutrient amount applied. If we use 200 pounds of 19-19-19, the nutrient available is 38 pounds each of N, P2O5, and K2O.
With the removal and applied nutrient determined, let’s look at the nutrient balance provided by 200 pounds of 19-19-19.
Phosphorus needed is 36 pounds, and applied is 38 pounds. Therefore, we are close to balanced with a 2-pound overapplication.
Potassium needed is 144 pounds, and applied is 38 pounds. Therefore, we are underapplying K by 106 pounds. Over time, the soil test level K in this field will drop below the critical level. You will need to make annual K fertilizer applications to reach our yield potential. To meet the K need in this situation, we need to apply 176 pounds of 0-0-60 along with the 200 pounds of 19-19-19.
We have not yet talked about the 38 pounds of nitrogen applied. Nitrogen rate is based on two factors yield potential and percent of legume species in the stand. Since this is a grass mix with no legumes, using a 3-ton yield potential, we would need 75 pounds of N. We meet half our N need with the 19-19-19. In this example, 80 pounds of 46-0-0 would need to be added.
With current fertilizer prices, making fertilizer application decisions for livestock producers has never been more challenging. Here are a few items to consider in soil fertility management for forages.
- Soil test if you have not tested in the last four years.
- Use the soil test report to prioritize soil fertility decisions.
- Is pH in the desired range for the species you are raising? If not, spend money on lime first.
- Prioritize P & K applications to the lowest testing fields (or field areas).
- Nitrogen is vital for pure grass stand yields.
Here are a few helpful references if you are looking for more guidance. The soil fertility page of our forage website is at https://go.osu.edu/foragefertility. If you are more pasture oriented, the Ohio BEEF Cattle Letter https://u.osu.edu/beef/search “fertilizer” has at least three recent articles of interest.