Accurate Manure Spreading State of the Art

Brian J. Holmes
Department of Biological Systems Engineering
University of Wisconsin-Madison

For years soil scientists have noted that farm fields close to farmsteads are over-fertilized compared to those farthest from livestock barns. Research surveys conducted by Peter Nowak, Professor, Department of Rural Sociology, University of Wisconsin-Madison, indicate that most livestock producers apply crop nutrients at a rate twice that needed by the crop. This occurs because fan-ners are not taking adequate credits for manure and legume plow-down when they order commercial fertilizer. Studies conducted by the Nutrient and Pest Management Program at the University of Wisconsin-Madison have shown rates of manure applications are underestimated by a factor of two.

These studies indicate that livestock farmers are over-fertilizing their crops because they lack confidence in their estimates of nutrients supplied by manure and/or how much manure is applied. Such over-fertilization can contribute to the high level of nitrogen, which is showing up in farm well water supplies. Studies by Sylvester (I 997) show that 9-14% of Wisconsin farm wells exceed the drinking water standards of 10 ppm of nitrate nitrogen. Other sources on the farmstead can also be contributing to this problem.

The USDA Natural Resources Conservation Service, has developed standards for nutrient management plans. These standards are the basis of how producers must manage nutrients if they are to qualify for state and federal financial assistance for various programs such as pollution control facilities and price supports on crops. Livestock producers, who have an National Pollutant Discharge Elimination System permit, must have a nutrient management plan. The standards require producers to apply crop nutrients to fields based on soil tests and crop uptake rates. Nutrient application in environmentally sensitive areas are restricted or prohibited.

Soil testing and a nutrient management plan can establish the best location and application rates for livestock manure. However, methods of determining application rates are still quite primitive.

Some ways to show livestock producers how to more accurately apply manure are:

1. Estimate the volume on a spreader load and calculate the weight on the load.
2. Use truck or platform scales to weigh representative spreader loads.
3. Weigh the manure deposited by the spreader onto a sheet of plastic following normal application procedures.

These methods can be used to obtain application rates somewhere close to those required.

However, they are more cumbersome than most producers are willing to accept and practice on a regular basis. To expect farmers to apply manure at an accurate rate, they need equipment that can apply manure precisely at a specified rate.

The development of equipment to more accurately apply manure has progressed on a variety of fronts. The techniques for measuring application rates have been based on manure consistency and off-the-shelf technologies, which can be configured to accomplish the task. When manure is sufficiently liquid, one solution is to select an inline flow meter to monitor the rate of manure being discharged. This equipment will not work for solid or semi-solid manure. Load cell technology is another method to measure application rate by monitoring the change in weight of a spreader over a given time interval.

Daniel Ess, Agricultural and Biological Engineering Department at Purdue University, has worked with Balzer Manufacturing, Mountain Lake, Minnesota, to develop a system for measuring the weight of a liquid manure spreader tank by installing load cells between the tank and spreader frame. Their work in this area has produced a commercially available spreader for liquid manure which uses subsurface injection.

Philip Goodrich, Department of Biosystems and Agricultural Engineering at the University of Minnesota, has developed a liquid manure spreader with variable speed pumps in each discharge tube leading to each sweep injector of a liquid spreader. Plans were to consider load cell technology to measure application rate on the go.

James Glancey (1 997), Department of Bioresources Engineering, University of Delaware, along with engineers from New Holland North America, have developed a rear discharge spreader capable of applying solid and semi-solid manure at a specified rate. Global positioning features allow for recording of application rates based on position. This same equipment can be used for variable rate manure application to achieve sitespecific nutrient management. The spreader uses load cells in the axle and hitch to measure the mass of the spreader load. Averaging techniques are used to reduce the variability of load measurements caused by equipment vibrations and field irregularities. The equipment can accurately apply material in the range of 1-5 T/acre.

Brian Holmes and colleagues at the Biological Systems Engineering Department, University of Wisconsin-Madison, are developing an accurate side discharge manure spreader using load cells in the spindles of the wheels and the spreader hitch to measure mass. The modified Gehl Company spreader discharge gate is positioned by a hydraulic cylinder controlled by a microprocessor. Efforts are underway to add global positioning equipment to incorporate site specific farming features.

Daniel Ess and Balzer Manufacturing have advanced their liquid manure spreader by incorporating a flow meter in the discharge line to replace the load cells. The operator can accurately adjust the application rate based on flow rate measurements and obtain a record of application rate based on position (application map) when using global positioning equipment. An added feature uses an on/off valve to turn off spreader discharge when the spreader enters no-spread zones such as drainage ways, stream corridors, sinkhole buffers, etc. These critical no-spread areas are mapped into the global positioning field map and the valve is automatically closed when the spreader enters these zones. Overlap avoidance can also be incorporated using these features. This equipment is currently available from Balzer Manufacturing.

Manure is increasingly being pumped from storage to field application through irrigation pipe/hose. Daniel Ess of Purdue has developed flow measurement equipment to more accurately apply this manure as well. Equipment similar to the tank spreaders has been added to obtain an application map and no-spread zones.

L & M Industries, Inc. of Bear Creek, Wisconsin, offers a custom manure spreading service. Their equipment incorporates a flow meter for determining the delivery rate to a tractor-drawn injection system. Ground speed radar equipment is used to establish field capacity. With the desired application rate and field capacity, the operator can calculate the correct forward speed. Hydro Engineering, Inc., Young America, Minnesota, offers a chart with their pumping equipment. The chart recommends a forward speed for injectors of different width to achieve a given application rate based on pump delivery rate.

Company and brand names mentioned in this paper are mentioned for the benefit of the reader and are not an endorsement of any product or service over another. They are the only companies the author is aware of which are offering these products or services. There may be other companies offering the same or similar products.

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