UF Research: Dairy Farm Manure Could Be Useful To Nurseries

November 29, 2001

GAINESVILLE, Fla. — Most manure produced by Florida’s dairy farms is stored in lagoons and spread on fields, a practice that can lead to pollution of rivers and lakes if not done correctly.

Now, University of Florida agricultural engineers have come up with an environmentally friendly and economically attractive use for the manure: Compost it and substitute it for peat commonly used by nurseries as a potting material.

“My work shows that dairy manure compost by and large is just as effective as peat in growing container-grown plants,” said Rafael Garcia-Prendes, who did the research for his master’s thesis in agricultural operations management. “Substituting it for peat could provide a way for dairies to reduce pollution problems while benefiting nurseries, which spend a lot of money for peat imported from as far away as Canada.”

With an average of 688 cows per farm, Florida’s 225 dairies have some of the largest herds in the nation, Garcia-Prendes said. The approximately 155,000 dairy cows in Florida produce at least 4 million tons of waste each year, the bulk of which is broken down slowly in lagoons and spread on fields as fertilizers, he said. If these systems are mismanaged, runoff can lead to nutrient pollution and declining water quality in streams and rivers. That has spurred increased scrutiny from government officials and tightened environmental rules.

To stay within the rules, dairy farms are trying to come up with inexpensive, effective waste treatment systems, Garcia-Prendes said. One strategy, adopted by a 2,000-cow dairy in Central Florida, is to turn the manure into compost using a so-called “drum” composter — a large cylinder that slowly turns the waste to speed up the natural composting process. While the process works, there is not enough of a market for the end product to justify the cost of buying and operating the drum or installing the system at other farms.

Garcia-Prendes’ study was aimed at the possibility of creating a new market for compost in Florida’s nursery industry. To see if the compost could be substituted for peat, a naturally occurring material used widely by the nurseries, he first compared the physical, chemical and biological characteristics of the two materials.

The research showed the two materials were largely equivalent, although there were a few differences. Peat tends to hold more water than compost.

Garcia-Prendes then looked at how well plants grow in peat versus compost, testing mixes composed of varying amounts of each material against each other. Results again showed that the materials were largely equivalent, with the compost outperforming the peat in some cases, he said.

“There are differences between peat and compost, but they are small enough that they would only require a difference in management, which would not be a big deal once nurseries got used to the compost,” Garcia-Prendes said.

Fred Gore, owner of Gore’s Dairy in Zephyrhills, Fla., where the drum composter is located, said he currently sells up to 200 cubic yards produced by the composter each week for $10 per yard. That doesn’t come close to the cost of purchasing and operating the composting system – which retails for around $150,000 — so the results of Garcia-Prendes’ study are encouraging, he said.

“Large dairies have to take care of the waste,” he said. “That’s why we’re in this: To try to find a viable way to handle waste without violating the regulations.”

Peat is mined from bogs and swamps, a process that can damage wetlands or other sensitive environmental areas, said Roger Nordstedt, a professor of agricultural and biological engineering and the chairman of Garcia-Prendes’ master’s thesis committee. So substituting composted manure for peat could have other environmental benefits.

“There are a lot of environmental pressures to not mine peat, so using composted manure could provide an alternative,” he said.

The drum composter and Garcia-Prendes’ project was funded through a $170,000 grant from the Environmental Protection Agency and the Florida Department of Environmental Protection.