March 7, 2008

First drought and now excessive mud have forage fields in Kentucky needing a little tender loving care. But that care can get expensive with today’s high fertilizer costs. To combat that, farmers need to apply fertilizer when it will give them the most return for their dollars.

Factors to consider for optimal forage production include proper soil pH, adequate phosphorus and potassium in the soil and nitrogen to boost plant growth. How much will be needed in additional fertilizer depends on a field’s use, forage crop grown and existing nutrient levels in the soils. 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,” Ray Smith, a University of Kentucky College of Agriculture forage specialist, recently told farmers. “Hopefully your soil test levels will be more than you expected.”

If the soil tests are in the high range of phosphorus and/or potassium, then no additional fertilizer is needed. In the medium range, fertilizer rates, similar to nutrients removed by hay or grazing removal, will be recommended. Higher rates will be recommended in the low soil test range.

If the test is in the upper part of the medium range, a farmer might reduce the recommended fertilizer application for this year or wait a year hoping for lower prices. This is because in the medium range, soil has enough potassium and phosphorus for production this year. However, the soil tests will rapidly fall if the removed nutrients are not replaced.

Each ton of cool-season grass hay removes about 12 pounds of phosphate and 50 pounds of potash. This would be 48 pounds of phosphate and 200 pounds of potash for 4 tons. Removal by grazing is much less, 4 pounds of phosphate and 16 pounds of potash. It is going to be important to get these nutrients back on the field fairly soon to maintain crop yields. Soil testing is a key to making these decisions.

Smith recommended splitting fertilizer applications to get nutrients to the plants when they need it most. Potassium and phosphorus can be applied to fields at anytime because it stays in the soil unlike nitrogen, which can be lost under certain conditions. However, Smith said recent studies have shown that winter freeze-thaw action makes potassium in the soil more available for the first spring hay cutting. So it may be best to put on half the amount needed after the first cutting of hay in the spring and save the other half for after the third cutting to get better growth throughout the summer. This would be especially important of alfalfa.

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

Instead, Smith said splitting nitrogen applications would be a good idea, especially based on university research trials. Applying 40 to 50 pounds in mid March to fescue or orchardgrass will boost yields for the first cutting in May while applying 80 to 100 pounds in March may not boost yields enough to offset the extra cost.

“It’s better to put out 40 to 50 pounds for the first cutting then put more out as the plant is regrowing for the second cutting,” he said. “If the weather turns dry like last year then save the nitrogen for fall application to build forage stockpiles for winter. If you are not cutting hay until the middle of June, then it’s probably not important to put any out in June because cool season grasses aren’t going to have much growth then.”

Smith said it is important for farmers to remember 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,” he said.

Smith said not to use nitrogen in grass fields that also contain 25 percent legumes. It will provide a yield bump but cause the grass to crowd out the legumes. Legumes fix nitrogen from air and provide it to nearby plants thereby providing some free nitrogen. Legumes also provide high quality forage; so it is important to keep them.

Finally, proper levels of soil pH are important to ensure plant growth. It also ensures efficient use of potassium and phosphorus. Lime is used to maintain proper pH.

“Fortunately lime is still one of the cheapest soil amendments that we have,” Smith said.

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