Liquid manure application in Iowa typically happens in spring and fall each year. The majority of liquid manure application takes place using a tank or a dragline applicator, providing additional nutrients to crops.
Tank applicators transport manure from the livestock facility to agricultural fields and apply manure using a tank-mounted tool-bar. For fields that are close-by, manure can be pumped directly to the dragline-mounted tool-bar. In either case, a pre-determined application rate is used to pump manure through a manifold, which distributes manure to the application points across the tool-bar.
“Environmental regulations require producers to make sure manure is being applied to agricultural fields in accordance with their manure management plans,” said Dan Anderson, assistant professor and extension agricultural engineering specialist with Iowa State University. “It is important to ensure that the nutrients for use by the crops are being applied in appropriate proportions.”
Variations in tank capacities, manure densities and the presence of foam can cause the application rate to be different from the target number, as can variations in drive speed. Application rate should be verified, and both tank and dragline applicators need to be calibrated to ensure accurate application.
Both distribution of manure and calibrating the applicators are covered in a pair of new ISU Extension and Outreach publications. “Distribution of Liquid Manure Application” (AE 3600) and “Calibrating Liquid Tank Manure Applicators” (AE 3601A) are both available through the Extension Store. A “Calibration Worksheet for Liquid Manure Tank Applicators” (AE 3601B) also is available.
Calibrate application rates
Calibration of the application rate, in terms of gallons per acre applied, can be achieved using an area volume method. For applicators without automated controls, the volume of manure applied in a given pass should be determined. Knowing the density of the manure and the area covered in the pass, the application rate can be determined. Instructions for determining density and coverage area are included in publication AE 3601A.
There are manure applicators who use tractor-mounted automated flow controls to achieve accurate application rates. In these cases, flow controllers use a flow meter with an actuator to govern the flow rate and, subsequently the application rate.
“The majority of flow meters are set at the factory for their rated measurements, which can potentially be different when used for manure application,” said Kapil Arora, agricultural engineering specialist with ISU Extension and Outreach. “The flow meters should be verified to ensure they are providing correct flow rate readouts to the flow controls.”
Aim for better distribution
Achieving calibration of the target application rates only provides an average amount applied on a per acre basis. This application rate is delivered to the manifold mounted on the tool-bar, which then distributes the manure to the application points. This distribution of the manure across the tool-bar swath should be uniform so the variability among application points is minimal. This distribution should be verified only after the calibration for the application rate has been completed.
Split manure application, manure application to soybeans, high total nitrogen testing manures, and use of the Maximum Return to Nitrogen Rate Calculator can all cause the manure application rates to be lower than what was previously being used.
“Distribution across the toolbar points can be verified by capturing the discharge from each point for a known time,” Arora said. “Care should be taken to set up the equipment as close to the field conditions as possible. Aim for as low a variation as possible in the captured discharge so that better distribution is achieved across the toolbar swath.”