Hay growers should use soil-test information to make sure they’re applying fertilizer when it will give them the most return for their dollars, says Ray Smith, University of Kentucky forage specialist. He says factors to consider for optimal forage production include proper pH, adequate phosphorus and potassium, and nitrogen to boost plant growth in non-legumes. Additional fertilizer needs depend on the field’s use, forage crop grown and existing soil nutrient levels. Phosphorus is important to the root system and yield, while potassium is critical for disease tolerance and winter survival.

“I would really encourage soil testing because hopefully you will have some pleasant surprises,” Smith says. “Hopefully, your soil-test levels will be more than you expected.”

If phosphorus and/or potassium are in the high range for your area, no fertilizer is needed. In the medium range, apply enough fertilizer to replace the nutrients removed by hay or grazing. Higher rates are recommended if soil-test levels are low.

If the test is in the upper part of the medium range, a grower might apply less than the recommended fertilizer rate or wait a year hoping for lower prices. In the medium range, soil has enough potassium and phosphorus for this year, but the levels will fall rapidly if removed nutrients are not replaced, say Smith.

Each ton of cool-season grass hay removes about 12 lbs of phosphate and 50 lbs of potash. Removal by grazing is much lower – 4 lbs of phosphate and 16 lbs of potash. It is important to get these nutrients back on the field fairly soon to maintain crop yields, and soil testing is an important tool, he says.

Smith recommends splitting fertilizer applications to get nutrients to the plants when they need it most. Phosphorus and potassium can be applied at any time because they stay in the soil. However, Smith says recent studies have shown that winter freeze-thaw action makes potassium more available for the first spring hay cutting. So, especially for alfalfa, it may be best to put on half the amount needed after the first cutting and save the other half for after the third cutting to get better growth throughout the summer.

“With any fertilizer product, it doesn’t hurt to meter it out throughout the year,” Smith states. “A year ago, we talked about getting a good yield increase with a spring application of 80-100 lbs of nitrogen, and you would make money. The way the price of nitrogen has gone up, I’m not confident at all to say that now.”

Instead, he believes splitting nitrogen applications would be a good idea. Applying 40-50 lbs/acre to fescue or orchardgrass in mid-March will boost the first-cutting yield, but putting on 80-100 lbs then may not add enough yield to offset the extra cost. “It’s better to put out 40-50 lbs for the first cutting, then put more out as the plant is regrowing for the second cutting,” he says. “If the weather turns dry, then save the nitrogen for fall application to build forage stockpiles for winter. If you are not cutting hay until the middle of June, it’s probably not important to put any out in June because cool-season grasses aren’t going to have much growth then.”

Smith reminds growers that the time to apply nitrogen to grass stands is when the grass starts growing. “The important thing is, if you say you can’t afford nitrogen this year, the first pounds you put on are the most efficiently used.” Don’t apply nitrogen to grass fields that also contain 25% legumes. It will provide a yield bump, but might cause the grass to crowd out the legumes.

Finally, proper soil pH is important for plant growth, and also ensures efficient use of potassium and phosphorus, he says.

Contact Smith at 859-257-3358.