Wheat-based farming is the dominant production system in the 250-to 600-mm rainfall areas in Australia. This type of farming may use a pasture-ley, a phase system, or a continuously cropped system . The ley system has short annual sequences of cereal crops separated with either short or long periods of legumebased pasture. With the phase system, the crop sequence is longer and can include pulse and oilseed crops as well as the cereals. Whatever the sequence of crops and pasture, the overarching farm objective is to provide an appropriate soil environment so that profitability is ensured without negatively affecting long-term sustainability. Farmers seldom follow strict rotations; rather, they develop flexible crop and pasture sequences based on rules that account for short-term goals and long-term environmental considerations. The rotations used must ultimately be consistent with providing a base for nitrogen and phosphorus fertility, an adequate soil structure associated with maintaining organic matter, and disease, pest, and
ing the cropping component in the rotation, assisted by reduced tillage systems, more retention of crop residues, and also an increase in nitrogen fertilizer use.