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Fluid Journal : Fluid Journal 1993-1995
Paul S. Belzer Point Injection: Viable Option for Growers Studies show improved field responses, minimal soil disturbance, reduced energy costs and increased fertilizer efficiency. Summary: Studies are showing that point injection fertilizer application (PIFA) is offering a positive, plausible application alternative for many growers. Spoke wheel, single probe, and high pressure applicators have been field tested over the past decade. Agronomic performance data for a variety of cropping regimes have been promising. Additional research is needed to expand on the agronomic relevance and benefits associated with PIEA. The bulk of point injection fertilizer application (PIFA) agronomic I research has thus far concentrated on the efficiencies of nitrogen placement and split timing in corn and small grains. A variety of data suggests that agronomic benefits can be anticipated through the use of PIFA. Before reviewing these field reports, a brief explanation is in order about the types of equipment developed so far that make PIFA work. Spoke wheel Although European and Florida prototypes probably predate it, the spoke wheel researched in FFF- sponsored studies during the mid-'80s by Baker et at. of Iowa State University is the model that stimulated much of the PIFA field studies in the Midwestern U.S. and Canadian prairies. The spoke wheel is a tractor- pulled wheel device that meters fluid fertilizer into a ported axle. Fertilizer flows from the spokes as the wheel rotates. The four to six spoke wheel units commercially available are mounted on a tool bar to accommodate variable row spacings and deliver fertilizer to the soil at eight-inch spacings to a depth of four inches. At forward speeds of 4 to 4.5 miles per hour, a spoke wheel applicator may use only one-third of the power required by certain knife injection systems. A spoke wheel with a good track record over some 50,000 acres in the western U.S. and Canada is one designed by Pattison Bros. of Lemberg, Saskatchewan. It consists of 12 hollow stainless steel spokes that penetrate the soil as the wheel turns. Fluid fertilizer is placed ("nested") at eight-inch intervals and 3 to 4 inches below the soil surface. Fluid fertilizer, under low pressure, is supplied to each spoke through the wheel hubs. A rotary valve located in the hub meters an accurate amount of fertilizer to each spoke. Both soil penetration and wheel protection under field conditions are afforded by a spring-loaded shank. A strengthened spoke tip makes for durability and the fertilizer outlet is set below the tip to prevent plugging. The spoke wheel has proven successful for UAN and other clear liquid applications. I am aware of only one spoke wheel applicator that was developed for the purpose of applying higher-nutrient-content suspension fertilizers. Almost ten years of field evaluation have produced design refinements for available spoke wheels. Concerns related to spoke plugging, coping with heavy trash, matching forward speed and fertilizer application rates, hub integrity, durability, and maintenance costs have been largely addressed by manufacturers. Future spoke wheel models will continue to be improved commensurate with acres covered. Single probe Aiming for the same agronomic traits as the spoke wheel, a single probe-type fluid fertilizer injector has been developed by Tompkins and Womac in a FFF-sponsored study at the University of Tennessee. The hydraulically driven single-spoke injector enters and exits the soil as the unit moves forward. Field evaluation of the prototype has revealed that a variable injection interval of 8 to 24 inches at a depth of about 2.5 inches can be achieved without significant disturbance. Further engineering research will be necessary to increase forward speed and improve soil penetration. A potential development regarding the probe injector is the linking of actuation with an "electronic eye" to ensure that fertilizer is applied only where plants are detected. 1 Fluid Journal Winter 1994
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