Written by: Matthew Jenkins, MoFCB 4R Specialist & Inspector
How does phosphorus removal by grazing compare to a field that is hayed instead? In the last blog, I showed an example where calves grazing a pasture could remove 10 lb/ac of P2O5. Assuming we have 3 calves/ac that weigh 500 lbs each and they eat 3% of their body weight, you would need approximately 2,700 lbs of dry forage per acre to have them on pasture for 60 days.
If you removed that 2700 lbs of forage as hay in early bloom instead (dominated by fescue) and don’t feed it back on the field 
you got it from, you would have removed around 23 lb/ac of P2O5. Thus, haying removes 130% more P2O5 than grazing. To keep from having to fertilize for the full haying removal, producers can feed hay by unrolling it where it was baled.
I called Consumers Oil and Supply in Braymer this morning (6/25/25) and priced MAP at $793.80/Ton. In this example, you would have saved $9.92/ac in phosphorus by feeding hay where it was baled, assuming it was unrolled evenly across the field when fed.
The previous example represents hay ground of moderate productivity, but in ground with high productivity, the deficit would be even larger. Let’s say the farm can produce double that amount of hay (5,400 lbs of dry forage). Now the grazing situation would remove around 20 lb/ac of P2O5, and the haying situation would remove around 46 lb/ac of P2O5. The difference of 26 lb/ac of P2O5 would cost $19.85/ac to replace.
The purpose of this exercise was not to show you how to estimate your phosphorus removal, as the estimate of % phosphorus in hay varies by soil fertility, plant maturity, and many more variables. However, it is clear that there is potential to save money by unrolling hay to evenly distribute the phosphate back on the field the hay was taken from.
Key Points
- According to the Small Ruminant NRC (2007), Kentucky 31 fescue hay in early bloom contains 0.37% phosphorus
-
P2O5 % (plant food P) = Phosphorus % x 2.29
-
MAP fertilizer contains 52% phosphorus
-
Hay P removal increases with increasing forage yield
-
For more information, refer to the previous blog titled, “P Removal by Grazing”