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Variable Rate Control In Liquid Manure Application

Matthew J. Robert
Matthew J. Robert
Research Engineer
Department of Agricultural Engineering
(217) 333-2611; mrobert1@illinois.edu

Direct application of manure on cropland, using vacuumloaded slurry tanks, is a very common way of utilizing swine manure in Illinois. New regulations require many livestock farmers to accurately account for the amount of fertilizer that is being applied to fields. With commercial fertilizers, global positioning systems (GPS) and flow meters can be used to apply the correct amounts of nutrients on fields with acceptable accuracy. However, very little technology is available for regulating spreading of manure to fields via slurry tankers, and not much research has been performed on variable rate or precision manure application equipment. The goal of this project is to develop a system that uses a simple, non-clogging pneumatic valve between the injection bar and the vacuum-loaded tank, thereby addressing the need for improved control and accountability.

We retrofitted a 2,500 gallon Top Air® tanker with a 6- inch Red Valve® pneumatic rubber pinch valve between the tank discharge and the injector toolbar. The valve is actuated by air supplied by a 12-volt piston air pump filling an air reservoir. An electrically controlled air regulator varies the air pressure on the pneumatic valve according to the control signal from the data logger. Air from the pump and reservoir is also supplied to a slurry pressure-sensing network through two stainless steel orifice plates. Inexpensive differential pressure transducers are used to record the air pressure differences between components of the system.

Results of the project so far show that the control system can do a good job of varying manure application rates, especially at low to medium flows. We plan to interface a commercial rate controller with the spreader this year and create a set of plans that a producer can use to build a variable rate controller for an existing slurry tank.

Figure 1
Figure 1. A 6-inch pneumatic valve being tested on a slurry tank with injection toolbar.

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