Manure Haulers Achieve Application Rate Goals
But 70% of manure haulers had poor spreader uniformity.
CSU’s nutrient management calculations result in a very precise recommended manure application rate. However, due to the variable nature of manure and the variability of application by solid manure spreaders, farmers usually can not apply manure as precisely as we can calculate a rate. The variability in manure spreading is due in part to equipment problems such as failure of beater bars to break up clods, variable rates of feed aprons, and sluffing of manure from the spreader sides during application. Very few manure haulers calibrate their manure spreaders; most feel that they can estimate the application rate based on experience and can adjust the spreader according to the wetness of the manure.
We worked with ten manure haulers to test spreader uniformity and calibration techniques. Two calibration methods were evaluated. The Tarp Method in which the spreader operator drives over three tarps, the manure on the tarps is weighed, and an application rate is calculated by dividing by the area of the tarps. The Swath Width and Distance Method requires truck scales so that the manure spreader can be weighed full and empty. The manure is spread, and the swath width and distance traveled is measured; then the rate can be calculated by dividing the weight by the area.
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The Swath Width and Distance Method resulted in significantly higher measured application rates than the Tarp Method. The variability across tarps averaged 30%; this amount of variability is innate to manure spreading. However, the application rate goals, stated by the manure haulers before spreading, were not significantly different from either spreader calibration method. Manure haulers applying manure for other producers are paid to apply a defined application rate, and most are achieving their application rate goals. We did not evaluate manure application rates spread by farmers on their own land.
Seven out of ten manure spreaders had spread patterns which were off-center. Some of the trucks did not seem to be loaded evenly, but trucks were loaded according to common procedure; therefore, the unevenness of the spreading could be partially attributed to asymmetrical loading and partially attributed to the need for adjustment and improvement of manure spreaders. Swath widths ranged from 7 ½ ft to 16 ft. Therefore, the haulers must adjust their overlap patterns depending on the swath width, in order to achieve a more uniform spread.
Both the Tarp Method and the Swath Width and Distance Method depend on the use of small tarps with 30% variability. A third method does not depend on small tarps, and can be used for field-scale determinations. The Loads per Field Method requires the hauler to know the acreage of the field and then to count the number of loads applied to a field. Based on the average weight of a load, the rate can be determined. Unfortunately, this method calculates application rate after the application is complete, when it’s too late to change the rate on that field.
