Department of Food

Department of Food, Agricultural and Biological Engineering

Articles Contributed to Ohio's Country Journal
Mid-September 2003

Applied Engineering

Manure: How much are you spreading?
Karen Mancl

Matching manure application rates to the nutrient needs of the crop is the core principle of a manure nutrient management plan. Through careful sampling of the manure and soil, an appropriate application rate can be calculated. OSU Bulletin 604 (the Ohio Livestock Manure & Wastewater Management Guide) steps through the application rate calculations. Even after all this care and consideration the management plan can fail if the actual application rate of the spreading equipment is unknown.

A study recently published by OSU in the Proceedings of the 9^th ASAE International Symposium of Animal, Agricultural & Food Processing Wastes examined the capability of livestock producers and growers to make visual estimates of manure application rates. Manure spreader calibration was demonstrated to 101 farmers at 6 field days.

Double the desired rate
At the beginning of each field demonstration, participants were asked if they had even seen this demonstration before, their occupation and their estimate of manure application based on their experience. Of the 101 participants, 13% estimated at or near the actual application rate. Some (22%) estimated high application rates with 2 estimating four times the actual application rate. Most (65%) underestimated the manure application rate with 50% estimating less than one-half the actual application rate.

So by relying on visual estimates, half of the livestock producers and growers surveyed would have applied at least double the desired application rate. The tendency to underestimate manure application, and therefore over-apply manure, reinforces the need to calibrate spreading equipment as a part of a manure management plan.

Trying to apply manure at the desired rate can be a problem. Most manure spreading equipment has not been calibrated. In a 1996 Minnesota study, Schmidt and others found that only 16% of farmers had their application equipment calibrated. In 1997 Hoban and others interviewed over 1000 North Carolina livestock producers. They found that 38% tested manure and 36% had calibrated their spreading equipment.

Calibrating your spreader
Manure spreader calibration is quick and easy, taking only 30 minutes to determine the application rate. For solid or semi-solid livestock manure, place three sheets of plastic out in a farm field. (Weigh each sheet first so you can subtract this weight later.) Spread the manure in the field, including the areas covered by the plastic sheets. Carefully gather and weigh the plastic and the manure to determine the amount of manure applied to each sheet. Based on the size of the sheet and the average weight of manure, the application rate is determined with this equation:

Lb. of manure * 22 _{=
tons of manure per acre}Size of sheet in ft²

OSU Extension fact sheet AEX-707, "Land Application of Waste: Spreading and Injection", describes the method and includes a table of application rates for several sizes of plastic sheet. To find out more request a copy AEX 707 and Bulletin 604 from your county Extension office or view them on the web at www.ag.ohio-state.edu/~setll.

To get a copy of “Farmer Estimates of Manure Application Rate” by K.M. Mancl and J. Dean Slates, presented at the 9^th ASAE International Symposium of Animal, Agricultural & Food Processing Wastes, contact Dr. Mancl and request a reprint.

Karen Mancl, professor and Extension water quality specialist, can be reached at 614-292-6007, or mancl.1@osu.edu This column is provided by the OSU Department of Food, Agricultural, and Biological Engineering.

This column is provided by the OSU Department of Food, Agricultural, and Biological Engineering.