Source: USDA-Natural Resources Conservation Service (NRCS) Ohio. Used by permission.
To calibrate commercial fertilizer applicators and planters, one should first set the equipment according to the manufacturer’s recommendations then fill the applicator or planter with a known amount of fertilizer. The equipment is then checked over a known acreage. Adjustments are made to achieve the planned rates.
There are several methods that can be used to calibrate the application rate of a manure spreader. The two best methods are the load-area method and the plastic-sheet method. It is desirable to repeat the calibration procedure two to three times and average the results to establish the most accurate calibration.
Before calibrating a manure spreader, the spreader settings such as splash plates should be adjusted so that the spread pattern is uniform. Most spreaders tend to deposit more manure near the spreader than at the edge of the spread pattern. Overlapping can make the overall application more uniform. Calibrating the application rates when overlapping requires measuring the width of two spreads and dividing by two to get the effective spread width.
Calibration should take place annually or whenever manure is being applied from a different source or the consistency is different.
The load-area method is the most accurate and can be used for most types of manure handling. This method consists of determining the amount (volume or weight) of manure in a spreader and the total area over which it is applied. The most accurate method to determine the amount of manure in a spreader is to weigh the spreader when it is full of manure and again when it is empty (portable pad scales work well for this). The difference is the quantity of manure applied over the area covered. Spreader capacities listed by the manufacturers can be used to determine the amount of manure in the spreader. However, care must be taken when using manufacturer’s spreader capacities. Heaped loads, loading methods, and manure type may vary considerably from what is listed by manufacturers of box- and side-delivery manure spreaders. Spreader capacities for liquid tankers are accurate, provided the tanker is filled to the manufacturer’s recommended levels, and no foam is present in the tank.
The area of spread is determined by measuring the length and width of the spread pattern. Measuring can be done with a measuring wheel, measuring tape, or by pacing.
The application rate is calculated using the following formula:
(Spreader capacity (tons or gallons) x 43,560 sq. ft per acre) ÷ (Distance traveled (ft) x Spreading width (ft)) = Application Rate (tons or gallons/acre)
The plastic sheet method can only be used with solid or semi-solid manure. This method of calibrating spreader application rates involves:
When calibrating manure spreaders, all details regarding tractor speed and manure spreader settings and date(s) of each calibration should be recorded with manure application information, and directly on the equipment. Mark equipment to ensure a known application rate is applied each time the referenced tractor speed and spreader settings are used. Manure spreader settings can include such things as: fast and slow settings on some box spreaders, gate position on side-delivery spreaders, and splash-plate position and fill levels on liquid tankers.
Place three to five buckets throughout the irrigation spray pattern and collect samples while operating the pump at a given rpm and pressure (for a traveling gun record the ground speed also). At the end of the planned sample period, measure the amount of liquid collected in inches (average the samples). Table 29 shows how many gallons per acre applied per inch applied.
| Table 29. Gallons Applied Per Inch of Liquid Manure Applied. | |
| Inches of Liquid Manure Applied by Irrigation | Gallons per Acre |
|---|---|
| 0.20 | 5,430 |
| 0.30 | 8,146 |
| 0.40 | 10,860 |
| 0.50 | 13,577 |
| 0.75 | 20,365 |
| 1.0 | 27,154 |
| 1.25 | 33,942 |
| 1.5 | 40,731 |
Alternative 1. Use a flow meter mounted on the injector system and calculate the distance and width to determine the amount applied over a measured area. Example: the flow meter measures 1,000 gallons over a distance of 600 feet and an area 10-feet wide.
Formula:
(Gallons Applied (1,000gal) x 43,560 sq. ft/acre) ÷ (Distance traveled (600 ft) x Application width (10 ft)) = Application Rate (7,260 gallons/acre)
Alternative 2. (Requires a 10- to 20-gallon graduated measuring container.)
Example: