Preface: Enduring prosperity for Farmland?

摘要

Australian cropping farms have been increasing innproductivity by 3–4% per year for some decades. Theirnprofitability, however, has barely increased during that timenowing to steadily declining terms of trade (Knopke et al.n2000). Burgeoning problems of land degradation, especiallynsalinity, waterlogging, and soil acidity, threaten to restrictnfurther increases in productivity and thence endanger thenprosperity of these farms.nThe causes of these problems are in principle wellnunderstood. The replacement of perennial deep-rooted nativenvegetation by shallow-rooted annual crops has resulted innwetter subsoils with concomitantly larger deep drainage,nleading eventually to rising water tables, waterlogging, andnoften dryland salinity. The removal of nutrient cations,nwhether in harvested products or by leaching as nitrates, is anlarge contributor to falling soil pH in the topsoil and uppernsubsoil.nThe essential difference, hydrologically, between nativenperennial vegetation and winter-active annual crops is that thennatives use substantial amounts of water in the summer, therebyncapturing any water that has drained into the deep subsoilnbelow the effective rooting depth of annual crops. There is littlendifference during the winter growing season in water usenby annual and perennial vegetation. Thus, it has long been advocatednthat deep-rooted perennial pasture species be incorporatedninto cropping systems to tap the water in the deepnsubsoil and thereby help control drainage from croplands.nPhase farming is one such way of incorporatingnperennials into a cropping system. It involves the tacticalnrotation of herbaceous perennial pasture, suitable for grazingnor for hay, with a series of annual crops. The perennialnpasture dries the subsoil below the roots of annual crops,nthereby creating a buffer in which water and nutrients thatnleak below the crops can be held for a few seasons,nremaining largely accessible to the roots of the next phase ofndeep-rooted perennials.nA forum sponsored by the Grains Research andnDevelopment Corporation was held in April 1998 to explorenthe role of phase farming in controlling the deep drainagenthat leads to detrimental rising water tables. Contributions tonthis forum formed the basis of this Journal Issue, whosenterms of reference were extended to include strip farmingnwith the woody species, tagasaste.