Division of Information Technology, Engineering and the Environment
School of Advanced Manufacturing and Mechanical Engineering
School of Advanced Manufacturing and Mechanical Engineering
Thesis Abstract
Yield loss due to weed competition and cost of weed control are significant expenses to crop production globally. With the increased adoption of sustainable no-till farming practices, weed control is obtained almost solely through spraying herbicides. In recent times herbicide resistance has developed in weeds such as annual ryegrass making them difficult to control by spraying alone. Mechanical destruction of weed seeds at harvest is a non-herbicide weed control method that aims to combat herbicide resistance. The unwanted material that exits a grain harvester (chaff) is known to contain a high proportion of weed seeds such as annual ryegrass. The Harrington Seed Destructor (HSD) is a machine that is towed by the harvester and uses a cage mill to process the chaff and kill the weed seeds contained in the chaff. The cage mill uses counter rotating sets of bars to impact the weed seeds up to 130 m/s. The HSD has some major operational limitations; it requires 150 kW, and weighs over 4.5 tonnes.
The aim of this project is to first identify the critical parameters that make the cage mill successful at destroying ryegrass seeds, then develop a prototype that satisfies this requirement but uses less power and occupies a smaller space than the cage mill. The Grains Research and Development Corporation (GRDC) have funded the development of the HSD and are funding this project.
Three particle impact testers were constructed and used to determine the critical impact energy to kill ryegrass seeds; a rotational impact tester; a drop weight impact tester; and a pendulum impact tester. The rotational impact tester showed a maximum seed kill of 34% at 67 m/s. However, the rotational impact tester was unable kill more seeds because the higher rotational speeds caused an air cushioning effect. Initial results have shown that the pendulum impact tester impacting individual seeds used less energy to damage seeds than the drop weight impact tester when impacting batch lots of seeds. The pendulum impact tester damaged 85% of ryegrass seeds at 0.013J/seed and it is the aim of any prototype weed seed destructors to achieve this impact energy.
An initial prototype weed seed destructor has been constructed using impact to damage ryegrass seeds at a lower peripheral velocity than the cage mill of 40 m/s. A method was developed to evaluate the seed kill of the prototypes. The method was shown to have acceptable repeatability (c.v = 6%). The current prototype was found to reduce the ryegrass seed germination by 70% when no chaff was processed with the seeds. However, when processing with chaff the prototype failed to reduce the ryegrass seed germination below the control. This was attributed to the chaff cushioning impacts. The next prototype is to address the air and chaff cushioning seen in the rotational impact tester and the initial prototype respectively.
