March 29, 2001 | By: Laura Skillman

Farmers often use animal manure and chicken litter to fertilize pastures and crops. By sending samples to the University of Kentucky, farmers can determine nutrient values in these products.

For about five years the UK College of Agriculture has been testing samples of animal waste for nitrogen, phosphate, potash, calcium, copper, iron, zinc and magnesium, said Frank Sikora, coordinator of soil testing. The tests can be used to determine the nutrient amounts that will be land applied to crops.

"The three most important elements that are critical in determining how much animal waste should be applied are nitrogen, phosphate and potash - the same three elements that are in commercial fertilizer," he said.

About 80 percent of the phosphate and potash in the sample is available to the plant while it varies with nitrogen depending on how it is applied, Sikora said. As a general rule about half of it is available to the plant. The remainder stays in the soil and can help with the buildup of organic matter.

The sample results from the UK lab are sent to the Cooperative Extension Service office in the farmer's county.

"The county agent gets the report and acts as the middle man to help the farmer determine how much to apply based on the test results," Sikora said.

A UK publication, AGR-146, also is available to farmers to aid in utilizing animal waste as fertilizer.

Nutrient management is part of the best management practices for livestock operations in Kentucky under the Kentucky Agriculture Water Quality Act. Guidelines for nutrient management plans are being written by the Natural Resources Conservation Service.

The nutrient management plans will have some rules about what should be looked at when calculating how much waste to apply.

"Unfortunately, in animal waste you can't vary what nutrients you have like in commercial fertilizer, so you have to accept what you have," Sikora said. "Also, unfortunately, animal waste has a lot more phosphate compared to nitrogen. So if you put the manure on based on nitrogen needs by the crop, there can be a tendency for phosphorus to build up over time."

Over the years, most universities have based their recommendations on nitrogen in the waste, but with the nutrient management plans the focus is going to be on phosphorus, Sikora said.

If the soil test reveals less than 400 pounds of phosphorus per acre with the Mehlich III test, then the waste application recommendations will be based on nitrogen. If it is higher, you may still be able to base it on nitrogen under conditions that minimize surface water movement of the phosphorus to streams.

Testing is not necessary with every land application but should be conducted periodically.

UK operates soil labs at Lexington and Princeton. Animal waste tests are performed only at the Lexington lab. The bulk of the samples sent to the lab are chicken and dairy samples with a few swine samples. Both liquid and solid waste samples can be sent.

To send samples for testing, farmers should contact their county extension office which will provide the proper containers and information needed for sampling. Turnaround time for results is a week once the sample is at the lab. The charge for the test is $20.


Frank Sikora, (859) 257-7355