Evolution of conservation agriculture in winter rainfall areas

The southern Australian broad-acre agricultural region lies south of latitude 32oS with mainly winter rainfall in the south and west, grading to equi-seasonal in the northeast region extending into central NSW (Figure 1). The major point of contrast with systems to the north (Chapter 5) is that summers in the south are generally too dry and hot for reliable production of dryland summer crops, and most farms,though a diminishing number, retain livestock enterprises. As a result, the systems comprise annual winter crops either continuous, or phased with annual or perennial pastures (2-5 years) grazed by livestock. The soils in the vast majority of the zone are either naturally deficient or depleted in the major crop nutrients (P and N) (Isbell 2002), and average annual rainfall is generally low (<550 mm) and extremely variable by world standards. As a consequence, extensive agricultural production involves significant attention to the management of business risk, due to the probabilistic nature of the outcomes of most important management decisions.