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 widespread duplex soils. This study investigated the productivity and water 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. The aims of the work were to evaluate the crops as alternative break crops to lupin on these soils, and to establish whether roots could proliferate in the clay layer, promoting both water extraction from the subsoil by that crop and improving yields of subsequent wheat crops. During the winter of the first season, a perched watertable developed for almost 3 months and some crops (especially lentil) grew poorly. Yields in the second season were generally good (lupin was close to the calculated potential yield and canola and Indian mustard were >2 t/ha), establishing that successful crops of oilseeds and grain legumes can be grown on this soil provided that there is adequate water without topsoil waterlogging. Yields of subsequent wheat crops were largest when following legume crops (40% in one season and 135% in the second compared with wheat following wheat or barley) but were also significantly greater following oilseeds (22% and 102%). Roots of cereals and pastures reached 80 cm in both seasons, whereas those of the oilseeds reached 60-80 cm depending on crop and season. Rooting depth of legumes varied 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, root mass differed between seasons; although on average, in mid September cereals and oilseeds had a smaller proportion (0.12 and 0.14) of total 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 any crop in either season and there was no evidence that tap-rooted legumes or oilseeds were better able than other crops either to exploit subsoil water for their own use or to create pores that subsequent wheat crops might exploit.