Yes, it may be considered adding insult to injury, but even that very mature, poor quality, lowly digestible, late made first cutting hay that was harvested this year took with it lots of soil nutrients. Fact is, each ton of hay that’s harvested and removed from a field in the harvest process takes with it roughly 13 pounds of P2O5 (phosphorus) and 50 pounds of K2O (potash). That’s regardless the calendar date or quality of the material that’s harvested.

To maintain productivity and plant health, fertility that’s removed needs to be replaced. Since P and K move slowly through the soil profile – perhaps only an inch or two a year – it’s probably best that what’s removed is replaced annually. And, since nearly all the phosphorus sources we presently have available include some nitrogen, those replacing fertility this fall will enjoy the benefit for grass based hay fields from the nitrogen that comes along with the P. That makes the next month or so a great time to replace the fertility that was removed this year.

The basics of fertilizing permanent hay fields are simple:

a) Soil Test, always soil test! Fertilizer is too expensive to apply if it’s not a yield limiting factor. If we don’t know what we presently have, we can’t possibly know what we might need! Contact your local OSU Extension office or fertilizer dealer for help finding a soil testing lab.

b) Read the soil test carefully or get help reading it. I’d discourage anyone from blindly accepting the fertilizer recommendations that sometimes are returned along with a soil test report. In some cases I’m not even certain I believe their little graphs that are sometimes found on the soil test results which indicate a sample might be high, medium or low in a certain nutrient. What I was told by one of Ohio’s labs when I asked how their recommendations are generated is that after they establish the nutrient levels in the soil through their laboratory procedures, the recommendations are typically generated based on the opinions of the company who might have submitted the sample for the land owner. This means, unless you send in the sample yourself, you may get back a recommendation based on data other than what Ohio State’s (or other midwest universities’) research might suggest is appropriate as published in OSU Extension Bulletin E-2567, Tri-State Fertilizer Recommendations. Ask your local Agriculture Educator for help in developing a recommendation if you have questions.

c) If one insists on fertilizing without the benefit of knowing the present fertility levels of the hay field, or if you know your present fertility levels meet or slightly exceed critical minimum levels, then it’s prudent to base your fertilizer application rates on actual or expected crop removal. As was mentioned earlier, each ton of hay removed takes with it 13 pounds of P2O5 and 50 pounds of K2O. No matter how you slice it, that’s a ratio of roughly 1 to 4, phosphorus to potash. Without benefit of a soil test to tell us otherwise, fertility needs to be replaced in that ratio when harvesting hay.

To put that into a little different perspective, consider that the average hay yield in Ohio is, and has been for decades a little less than 3 tons per acre per year. At a 1 to 4 ratio, that’s about 13 and 50 pounds respectively multiplied times the 3 tons of crop removal, or 39 pounds of P2O5 and 150 pounds of K2O per acre. As an FYI, since corn grain only removes about 0.27 pounds of K2O per bushel, it would take a yield of over 555 bushels of corn to remove the same amount of potash that an average Ohio hay yield removes annually!

To recap . . . you can’t starve a profit into any crop, sometime before winter dormancy is an excellent time to apply fertilizer to a hay field, and one ton of hay removes P and K in a ratio of roughly 1 to 4, or 13 pounds P2O5 and 50 pounds of K2O. To maintain fertility, health and the productivity of your forages, P and K must be replaced with either fertilizer or manure nutrients . . . 1 to 4, 13 and 50, per ton of hay removed!