Manure application equipment as well as irrigation equipment should be calibrated on a regular basis to determine accurate application rates. You should be able to accurately determine how many gallons, tons, cubic yards, or inches of manure or irrigation water you apply to a field.
Follow manufactures recommendation for calibration and/or refer to information on calibration of equipment given below and in the Publications and Articles. Calibration worksheets are located in there and can be used to calibrate various manure application and irrigation equipment.
For an additional guidance, including video tutorials, on calibration of liquid and solid manure spreading equipment, click HERE.
An "application rate" - whether it is manure, fertilizer, or herbicide - is defined as the amount of material applied per unit area of land. For manure, it is usually expressed in tons per acre (solid or semi-solid) or gallons per acre (liquid, or slurry), as follows:
Application Rate = Amount Applied (tons, gallons) / Area covered (acres)
So, to calibrate a manure spreader, you need to have reliable estimates of both amount applied and area covered. There are a number of different ways to estimate each parameter. Each of four methods is presented below.
Method 1. Based on Single Spreader Load: Solid, Semi-solid, or Liquid
1. Estimate amount applied, or spreader capacity, based on one of following:
Note: Manure density (weight per cubic foot) varies with moisture content, primarily depending on amount of bedding. For a more accurate estimate, weigh a five-gallon pail of manure, then multiply the weight by 1.5 to get the density in pounds per cubic foot.
Weigh spread load directly - If you have access to scales, weigh spreader full, then subtract spreader weight empty to get weight of manure. Convert to tons or gallons.
2. Estimate area covered by one spreader load by doing the following:
Spreader width (ft) x Distance (ft)/43,560 sq ft = Area (acres)
3. Calculate manure application rate by dividing amount applied by area covered:
Application Rate = Amount Applied (tons, gallons) / Area covered (acres)
Manure Conversions:
1 ton = 2000 pounds
1 cubic foot = 7.5 gallons
1 bushel = 1.25 cubic feet
1 gallon = 8.3 pounds
1 cubic foot = 62 pounds (wet) to 55 pounds (dry)
Method 2. Application Rate Based on Spreader Loads Applied to a Field: Solid, Semi solid, or Liquid
Application Rate = (No. loads x tons or gallons per load) / Field acreage
Method 3. Application Rate Based on Plastic Sheet Subsample: Solid or Semi-solid
This method involves measuring the amount of manure spread on a plastic sheet of known area (20 to 40 sq ft is a reasonable size). It is most useful where making an accurate estimate of spreader capacity is difficult, e.g. a heaped box spreader.
Method 4. Average Application Rate Based on Storage Volume Applied to Fields
This is not a calibration method in the same way as the others described here, but it is a way of estimating the average rate of manure applied to fields after emptying your manure storage. You need to know the capacity of your manure storage or an estimate of the portion applied on a given acreage.
Application Rate = Manure storage emptied (tons or gallons)/Area covered (acres)
If you know storage capacity only in volume (cubic feet), convert to gallons or tons using the conversion factors given earlier.
Adjustment to Obtain Desired Rate
Whichever calibration method is used, you will probably need to adjust the application rate to obtain the rate, or different rates, desired. Do this by changing a combination of tractor speed and spreader control. Then recalibrate the spreader by the same method. When the desired application rate is obtained, record the tractor and spreader settings for future reference. You may need to establish two or more rates for different crop types or varying nutrient needs.
Bibliography
Jokela, B. 2004. Manure Spreader Calibration. University of Vermont Extension Publication.