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Abstract
Lucerne (
Medicago sativa
L.) helps to prevent soil salinisation in the Western Australian
Wheatbelt by reducing recharge to saline water tables. There is broad consensus,
though, that it is not sufficiently profitable to motivate producers to plant it at the
intensity at which considerable off-site benefits would be conferred. This paper
employs a multiple-phase optimal control model to explore the value of this perennial
pasture for the management of herbicide-resistant annual ryegrass (
Lolium rigidum
Gaud.) in a crop–pasture rotation, given the difficulty of observing this value in
practice. The availability of selective herbicides for efficient weed control is found to
determine whether or not it is profitable to adopt lucerne pasture under optimal
management. Herbicide resistance requires producers to employ costly, non-selective
treatments for in-crop weed control. Thus, it motivates the adoption of perennial
pasture in which cost-effective forms of control can be implemented. Moreover, this
result is robust to feasible changes in the current economic environment.