Using a Flow Meter to Apply a Target Rate
To apply a predetermined amount of nitrogen, the specific amount of lagoon water that will supply the pounds of nitrogen needed is injected into the fresh irrigation water. A throttling valve or pump controller is used to adjust the flow rate from the lagoon so that the gpm on the flow meter display matches the target flow rate.
In order to calculate what flow rate to use, you will need to know
- the rate of nitrogen (lbs/acre) you want to apply,
- the concentration of nitrogen in the lagoon water, and
- how long it will take to irrigate the field.
Knowing this information, you can calculate the lagoon flow rate (gpm) needed by hand, using tables, or with an Excel spreadsheet.
These instructions for using a flow meter and throttling valve to apply a specific application rate of lagoon liquid manure nutrients assume you are using tables, but may also be helpful when using the other calculation methods.
If the gpm that is needed to apply the nitrogen rate you want is lower than recommended for the pump or too low to maintain a fast enough velocity in the pipeline to prevent solids from settling, you may wish to run the pump at a higher flow rate but for only part of the irrigation on each check or set. Instructions how to do this are included above, and tables and additional instructions are here:
Starting and stopping the pump might not be a practical long-term method of dealing with low target flow rates in your situation. This publication discusses other options for setting up a system that will be easier to operate:
This field data sheet has a place to record the instructions to the person doing the irrigation on where to set the flow rate or how long to run the lagoon pump, in addition to places to record the run times, gallons applied, and weather data for each field.
Recordkeeping tools for use with meters are here: