No abstract

A range of plant and environmental variables is known to influence the efficacy of herbicides. This paper explores whether environmental factors influencing efficacy of a herbicide can be quantified by analysing a set of industry data involving 59 experiments conducted throughout Australia in the years 1986–1995 for clodinafop‐propargyl on Avena spp. A spline method was used to analyse the combined data set of observed and interpolated covariates. In addition to dose, it was found that efficacy was significantly influenced by maximum temperature on the day of application, spray water volume, the interaction of maximum temperature and spray volume, the sum of minimum temperatures experienced in the 7 days prior to application, and the soil moisture deficit estimated for day 10 prior to application. The findings are discussed in relation to testing of new products for providing commercial factor‐adjustment information as an additional, marketable outcome of existing product testing procedures. Advantages of the spline model over the commonly used log–logistic model for evaluating dose–response and factor‐adjustment relationships are presented.

This study examines the use of water by existing downstream entitlement holders and their possible market interactions with upstream interests in new forestry plantations in the case of the Macquarie River Catchment, NSW. Demand for offset water to allow upstream plantation establishment is estimated as a function of tree product value and direct and opportunity costs in six sub-catchment areas with different rainfalls and locations with respect to urban and other high security water users (UHS). This upstream demand is aggregated with downstream demand for water. The aggregate supply of downstream water entitlements is posited in terms of marginal values to each of three sectors [stock & domestic (S&D), irrigation (IRR), and wetland (WL) areas] and their current entitlements. Assuming a fixed quantity of water entitlements, equilibrium quantities traded and the distributions of trade and associated surpluses are estimated given each of four stumpage values for tree products. This is done assuming four combinations of scenarios: with or without the policy that water entitlements must be obtained before establishing a tree plantation, and with or without one sub-catchment being very salty, the latter being a hypothetical case.

Large-scale tree plantations in high rainfall upstream areas can reduce fresh water inflows to river systems, thereby imposing external costs on downstream irrigation, stock and domestic water users and wetland interests. We take the novel approach of expressing all benefits and costs of establishing plantations in terms of $ per gigalitre (GL) of water removed annually from river flows, setting upstream demands on the same basis as downstream demands. For the Macquarie Valley, a New South Wales sub-catchment of Australia's Murray-Darling Basin, we project changes in land and water use and changes in economic surpluses under two policy settings: without and with a policy requiring permanent water entitlements to be purchased from downstream parties, before plantation establishment. Without the policy, and given a high stumpage value for trees ($70/m 3 ), upstream gains in economic surplus projected from expanding plantations are $639 million; balanced against $233 million in economic losses by downstream irrigators and stock and domestic water users for a net gain of $406 million, but 345 GL lower mean annual environmental flows. With the policy, smaller gains in upstream economic surplus from trees ($192 million), added to net downstream gains ($138 million) from sale of water, result in gains of $330 million with no reduction in environmental flows. Sustaining the 345 GL flow for a $76 million (406-330) reduction in gains to economic surplus may be seen to cost only $0.22 million/GL; but this is much lower than the market value of the first units of that water to agriculture and forestry.

This article reports on a study of the impact of risk on farm management practices in northern Syria, focusing particularly on how these are a¡ected by risk aversion and farm size. The study is based on production data from an eight-year ¢eld trial and on prices from market surveys. A large linear programming model is built, representing the eight years as observations from a discrete probability distribution. Risk aversion is modelled by inclusion of a utility function with constant relative risk aversion, represented using the DEMP/UEP approach.