1. School of Environmental and Rural Science, Univ. of New England, Armidale, NSW 2351, Australia (corresponding author).
2. School of Mechanical and Electrical Engineering, Univ. of Southern Queensland, Toowoomba, QLD 4350, Australia.
3. Professor, National Centre for Engineering in Agriculture, Univ. of Southern Queensland, Toowoomba, QLD 4350, Australia.
4. National Centre for Engineering in Agriculture, Univ. of Southern Queensland, Toowoomba, QLD 4350, Australia.