In traditional fumigation, the product is injected below the surface of properly prepared soil and applied in a narrow band as the fumigation equipment moves across the field. The surface of the soil is sealed or compacted by pulling a ring roller behind the fumigation equipment or behind a second tractor.
The oldest fumigation rigs operated via gravity flow. The rate of flow of fumigant from the barrel is controlled by valves and orifices (small brass or stainless steel disks with small holes in them). Rate of flow can also be controlled by a wheel which runs on the surface of the ground and operates a small pump. The tank holding the fumigant can also be pressurized by a cylinder of nitrogen. Rate of flow is controlled by pressure, orifice size, and rate of movement across the field. Shanks with multiple openings have been developed to improve distribution in soil types in which fumigants do not move well or for use with Metam-sodium which only moves a few inches in the soil. Following application, the actual depth of insertion of the shanks can be determined by observing the depth to which rust has been worn off.
Different depths of injection and shank spacings are used for different situations. Local Farm Advisors, PCA's or professional applicators can be consulted for suggestions on particular applications. In general, deeper injections and closer shank spacings provide increased control in well prepared soils but also require a slower speed and more powerful equipment to achieve and so increase the cost of the application.
Commercial applications of Methyl bromide are typically applied with relatively massive pieces of equipment capable of applying the product with computerized accuracy, laying a tarp, and gluing together adjacent edges in one operation. This relatively simple looking fumigation apparatus consisting of a cylinder of methyl bromide pressurized by a second (smaller) cylinder of nitrogen connected via a flow meter to a fumigation shank accomplishes the same basic operation as the more complex appearing equipment (minus the laying of the tarp).
In summary, no matter how complex or simple the apparatus, the function of a fumigation rig is to inject a liquid or gas beneath the surface of the soil where it will spread a foot or more in all directions from the point of injection through the air in soil pores and dissolve in the film of moisture surrounding the soil pores to kill nematodes.
Although typically used to apply fumigants in preplant situations, the same equipment combined with Coulter cutters to slice the surface has been used to apply nonfumigant nematicides and insect parasitic nematodes to turfgrass. A variety of different types of equipment have been developed in recent years to use with fumigation equipment in place of traditional single depth shanks to provide better distribution in soil of Metam-sodium products which on their own will only diffuse about 4 inches through the soil.
These shanks have 3 spray nozzles in the back to inject product at 3 different depths.
Behind each of the wedges on this shank is a spray nozzle. The wedges help provide better mixing of the product in soil, but also require more powerful equipment to pull them through the field than more streamlined shanks.
This spray rake has nozzles at 4 inch spacings. It is designed to be pulled through a preformed bed followed by a bed shaper to smooth and seal the soil surface.