YIELD RESPONSES OF WHEAT AND OTHER CROPS TO AGRONOMIC PRACTICES ON DUPLEX SOILS COMPARED WITH OTHER SOILS IN WESTERN-AUSTRALIA

A survey of experimental results relating crop management to grain yield was conducted for wheat and other crops on duplex and non-duplex soils in the wheatbelt of Western Australia. Increases m gram yield of wheat due to improved agronomic practices on duplex soils were almost as great as on other soils. Early sowing improved yield more on duplex soils than on other soils, but the response to applied nitrogen was more variable, possibly related to the reduced efficiency of uptake of applied nitrogen. The yield advantage for a semi-dwarf cultivar (Aroona) over a tall cultivar (Gamenya) was less (6%) on duplex soils than on other soils (29%). The optimum seed rate was 27% greater on duplex than on other soils. Increases in both gram yield and gram quality due to the application of potassium were large on 1 duplex soil. Water use efficiency in grain production was similar on duplex and other soils where seasonal water use did not exceed about 350 mm. At 1 location in the eastern wheatbelt, yields of wheat, barley, lupins and peas grown on a duplex soil were compared with yields on 2 other soils. Wheat was the most productive crop on the duplex soil, while barley yielded most on the other soils. All crops, except lupins, yielded less on the duplex soil. Experiments with 2 lupin cultivars grown on duplex and other soils on the south coast of Western Australia (average growing season rainfall >300 mm) showed that both cultivars yielded less on duplex soils, but 1 cultivar required slightly fewer plants to achieve its maximum yield on the duplex soils. This survey of experimental results in Western Australia shows that duplex soils are no less productive than other soils when results are averaged over all crops and locations. We conclude, however, that different management practices may be required to improve yields on duplex compared with other soils.