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Smart Spreader Will Improve Manure Management

In Wisconsin, 70 percent of dairy farmers surveyed haul manure daily, most without accurately knowing the amount they are applying to fields. A prototype manure spreader, developed at the University of Wisconsin-Madison, can deliver a predetermined amount of manure to the field and may lead to better manure management.

Only 2 percent of Wisconsin farmers credit nutrients from applied manure within 10 percent of the university guidelines, says Peter Nowak, a rural sociologist at UW-Madison”s College of Agricultural and Life Sciences. Nowak surveyed 1,400 Wisconsin farmers and found over-applied manure was largely responsible for excess nitrogen, phosphorus and potassium on farm fields. Excess nitrogen contaminates groundwater. Excess phosphorus runs off into lakes and streams and promotes algae growth, reducing water quality.

Farmers who want to credit nutrients from manure applications currently have three options: estimate the volume of spreader loads and calculate the weight based on previous calibrations with truck scales; use book values for manure density; or capture manure on a plastic sheet during spreading, weigh the sheet, and calculate the application based on the area of the plastic. These methods are cumbersome and have limited accuracy.

Brian Holmes, a researcher in the CALS Department of Biological Systems Engineering, and graduate student Paul Paluch have developed a prototype side-discharge manure spreader. The computerized spreader can apply manure within 10 percent accuracy based on the rate the farmer specifies. The operator simply keys in the amount to apply and the spread width of the manure.

The manure spreader has five load cells, one in each axle and one in the hitch. The control system constantly takes weight readings from the load cells, and the computer averages the weights and compares them with a previous average to determine the amount
of manure applied. The system also monitors ground speed. The computer uses the weight applied, distance traveled, and spread width to calculate the spreader”s application rate.

A hydraulic cylinder operates the discharge gate on the manure spreader to adjust the application rate. “The computer calculates the appropriate rate and sends it to the controller. The controller signals the cylinder to open or close to adjust the discharge rate,” said Paluch. “The computer calculates how much is being applied and checks it against the weight the farmer requires.”

At a certain speed, the spreader can attain only limited application rates. “The computer will signal the operator to change speed if the required application rate can not be achieved,” said Holmes.

The next phase in the development of the manure spreader prototype is to increase the spreader”s accuracy by 5 percent and to add variable rate application technology, which could be used with global positioning systems (GPS). “It isn”t much of a step from where we are now,” said Holmes. The development of GPS add-ons will start this summer.

Although the cost of the system has not been evaluated, all of the equipment used on the prototype is already in the market. “The computer processor is the only specialty component,” said Holmes. “Other specialty components aren”t needed.”

Incentives or cost-sharing may be important for farmers to adopt the technology. Side-discharge spreaders, without the add-on, may cost $5,000 more than box spreaders.
“If the technology is designated a best management practice, those interested may include people who receive cost sharing in priority watersheds, farmers with over 1,000 animal units, and custom-hauling contractors,” said Holmes.

“We are very pleased by the amount of industry support this project has received,” Holmes said. Funding for the prototype has been provided by the Wisconsin Fertilizer Council, the Farm Bureau Research Foundation, and several equipment manufacturers.

Holmes will be exhibiting the spreader at Farm Progress Days on the Siemers family farm in Manitowoc County, July 22-24. There will also be a similarly outfitted liquid manure spreader on display from Purdue University.