Fluid fertilizer injector development based upon dynamic response of in situ soil subjected to impact loading

An experimental machine for injecting fluid fertilizer into the soil at discrete increments with minimal soil disturbance was developed. The design featured a probe-type injector, the design of which was based upon measurements of dynamic soil response to impact loading. A microcomputer-based data acquisition system was developed and employed for high-frequency monitoring of a probe impacted into the in situ surface of clay loam, fine sandy loam, and silt loam soils. Data defining impact force on the probe versus depth of penetration were obtained for probe diameters ranging from 9.5 to 19.1 mm and probe striking velocities ranging from 2.0 to 5.0 m/s. Results showed that final probe penetration depth strongly affected peak probe force. A regression model based upon input energy, probe diameter, and penetration depth was developed to predict peak impact force on a probe. Dynamic soil characteristics were measured to quantify the soil conditions used in the penetration tests. Soil specimens were tested in a torsional-type resonant column device, employing a method developed to test agricultural soils at low confining stresses. Measured shear modulus, damping ratio, and strain amplitude ranged from 13.1 to 38.1 MPa, 0.89 to 4.04 percent, and 4.9 x 10^-5 to 11.9 x 10^-5 cm/cm, respectively. Generally, shear modulus decreased and damping ratio increased with an increase in strain amplitude. A prototype injector employing a kinematically inverted slider-crank mechanism was evaluated. Vertical orientation of the mechanism allowed a member, or probe, to engage soil during injector travel. Horizontal probe tip velocity offset injector travel velocity. A hydraulic-based actuator system controlled this velocity relationship. The probe released fluid through the tip during soil penetration. A custom-built fluid dispenser system integrated with the probe mechanism consisted of a pressure-regulated source, rotary timing valve, rotary fluid distributor, and probe tip valve. Fluid injection occurred at 400-mm intervals at a soil depth of 65 mm. Steady flow through the probe tip was described with a modified orifice flow equation. Reduction in intermittent flow rate with increasing crank speed was described with a decaying exponential function.