ALTERNATIVE CROPS FOR DUPLEX SOILS - GROWTH AND WATER-USE OF SOME CEREAL, LEGUME, AND OILSEED CROPS, AND PASTURES

Lupin is the major break crop used by farmers in Western Australia but neither lupin nor wheat uses much water from the B horizon of the wid espread duplex soils. This study investigated the productivity and wat er use of a range of crops and pastures during 2 seasons on a shallow duplex soil, with a sandy layer 30-40 cm deep, at East Beverley, WA. T he aims of the work were to evaluate the crops as alternative break cr ops to lupin on these soils, and to establish whether roots could prol iferate in the clay layer, promoting both water extraction from the su bsoil by that crop and improving yields of subsequent wheat crops. Dur ing the winter of the first season, a perched watertable developed for almost 3 months and some crops (especially lentil) grew poorly. Yield s in the second season were generally good (lupin was close to the cal culated potential yield and canola and Indian mustard were >2 t/ha), e stablishing that successful crops of oilseeds and grain legumes can be grown on this soil provided that there is adequate water without tops oil waterlogging. Yields of subsequent wheat crops were largest when f ollowing legume crops (40% in one season and 135% in the second compar ed with wheat following wheat or barley) but were also significantly g reater following oilseeds (22% and 102%). Roots of cereals and pasture s reached 80 cm in both seasons, whereas those of the oilseeds reached 60-80 cm depending on crop and season. Rooting depth of legumes varie d from 70-80 cm for field pea to 30-50 cm for chickpea and faba bean, with lupin extending to 60 cm in both seasons. As with shoot mass, roo t mass differed between seasons; although on average, in mid September cereals and oilseeds had a smaller proportion (0.12 and 0.14) of tota l mass below ground than the legumes (0.24) and pasture species (0.18) . Only a few millimetres of water was extracted from the subsoil by an y crop in either season and there was no evidence that tap-rooted legu mes or oilseeds were better able than other crops either to exploit su bsoil water for their own use or to create pores that subsequent wheat crops might exploit.