A laboratory evaluation of waterjet cutting of crop residue using the Aqua-Till® liquid coulter

Abstract

Ultra-high pressure (UHP) waterjet cutting technology is used across a multitude of industries. An agricultural application recently developed by the South Australian No-Till Farmers Association consists of an innovative crop residue cutting ‘liquid coulter’ - known as Aqua-Till®. The wheat straw stem cutting capacity of the device was evaluated under controlled laboratory conditions at the University of South Australia, using a purpose-made straw holding tray moving at a controlled speed under the path of a stationary UHP nozzle. The impacts of technology settings and straw conditions were measured. The cutting performance was assessed based on the degree of fully cut straw stems, integrating the extent of partially cut stems, from a quantity calibrated to an equivalent dry stem load in Mg/ha. Results showed that when operated at 380 MPa pressure, the device delivered very high cutting capacity of wheat straw stems of 10−35 Mg/ha across the range of nozzle orifice diameters (0.15-0.3 mm) and forward speeds (6−12 km/h) tested. The UHP waterjet cutting unit was found to operate most effectively when the residue was wet and placed under compression. Halving travel speed increased the cutting capacity by an average 12 % indicating a non-linear impact of speed. No effect of nozzle to target distance could be detected over the 5−70 mm range tested. The cutting performance of wet, compressed residue was mapped against the water volume rate required over a range of speeds and orifice diameters. Correction factors for extending cutting performance estimations to dry and/or loose residue conditions were also determined. Across the range of nozzle orifice diameters and speeds investigated, the laboratory data for wet compressed residue indicate that a nominal 150 L/ha volume of water, deemed acceptable under Australian dryland cropping conditions, could provide straw stem cutting capacities of up to 12.5 Mg/ha, 19 Mg/ha and 35 Mg/ha at 300 mm, 500 mm and 1000 mm nozzle row spacing, respectively, at a nominal 380 MPa operating pressure. In this study, the waterjet technology demonstrated very effective residue cutting, which could be maximised under specific residue conditions and technology settings. The results indicate that the technology could become an effective tool for assisting residue handling in no-till planting applications, particularly in wet stubble and soft soil environments where traditional mechanical coulters fail. Further research is required to develop accurate operational guidelines for a range of field residue type and conditions, as well as clarify the technology cost-effectiveness in order to facilitate adoption within the no-till cropping industry.