20 November 1998

Wheels might beat injection bugs

LIQUID fertiliser injection is not a new concept, its agronomic and environmental benefits have been recognised since the early 1960s.

But a big criticism of the technique, according to Regent Fertilisers, has been the principle of the application equipment, to date confined to the use of knife injectors.

Problems associated with this method, says the company, include potential damage to plants caused by the knives being drawn through the soil, a high draft requirement and compaction problems, drawbacks Regent maintains it has overcome with its Spoke Wheel injector.

A Canadian design, the three-point linkage mounted applicator comprises a 500-litre (193gal) capacity spray tank fitted with a standard Ramsey Injection centrifugal pump and pressure manifold system. At the business end are 16 ground-driven wheels mounted on a 6m (19.7ft) hydraulically folding toolbar.

Around the circumference of each wheel are a number of hollow spoke injectors, each having a wide side orifice protected by a tungsten alloy tip. As the wheels revolve, these spokes penetrate the soil up to a depth of 10cm (4in).

At the heart of the system is a ball valve, located inside each wheels hub, with an upper inlet port leading into a small central reservoir off which runs a lower, vertical, outlet port.

In operation, fertiliser solution is pumped at a predetermined constant pressure – normally 1.5 bar – from the tank, via restrictors in the spray lines, into the hub valve. It is held here until a spoke lines up with the outlet port – alignment governed by means of a timing indicator on each hub.

At this point, a metered amount of fertiliser is injected into the soil, the inner rim of the wheel closing off the valve until the arrival of the next injector spoke.

A ball indicator for each wheel enables the operator to monitor flow rate, while the combination of pressure and the design of the tip is stated to minimise the risk of blockage.

Operating speed of the unit is 6kph. Application rates, from 50-1500 litres/ha (8-236gal/acre), are varied by altering the pressure in the pump manifold and inserting larger of smaller diameter restrictors in the spray lines.

To allow a degree of row following, injector wheels are carried on a swivelling arm – fitted with a spring loaded breakback system – independently mounted on the toolbar to enable each to be positioned to cater for different crop row widths. &#42

Above: Regent Spoke Wheel liquid fertiliser injection system is described as overcoming the problems associated with knife injectors. Right: The business end… Metered amount of fertiliser solution is injected into the soil each time a spoke aligns with the outlet port of a ball valve located within the hub of each spoke wheel.