A comparison of the adaptation of yellow lupin (Lupinus luteus L.) and narrow-leafed lupin (L-angustifolius L.) to acid sandplain soils in low rainfall agricultural areas of Western Australia

Almost the entire lupin industry of Western Australia is based on the singl e species Lupinus angustifolius L. (narrow-leafed lupin), which is very wel l adapted to coarse-textured, mildly acid soils. However, L. angustifolius is not well suited to the strongly acid sand plain soils along the low rain fall fringe of Western Australia's agricultural areas, and alternative grai n legume species may be preferable. These soils, known locally as wodjil so ils, have very low nutrient contents, often high levels of extractable Al i n the subsoil, and are common in areas where severe brown spot and root rot disease is caused by Pleiochaeta setosa. Yellow lupin, Lupinus luteus L., may be a better species on these soils. This paper describes a series of trials comparing the grain yields of narro w-leafed lupin and yellow lupin on a range of soils in the agricultural are as of Western Australia. These trials were sown on a range of dates and in a range of rotational backgrounds between 1995 and 1998. With current culti vars, narrow-leafed lupin clearly has higher yield potential than yellow lu pin when soil-extractable [Al] at a depth of 15-25 cm (measured in a 1:5 ex tract of soil in 0.01 M CaCl2) is <10 mg/kg. When extractable [Al] at this depth is greater, yellow lupin can produce greater yields than narrow-leafe d lupin, depending on other environmental characteristics, especially when extractable [Al] exceeds 28 mg/kg, but its yield advantage is often small. Yellow lupin is less sensitive to delayed sowing than narrow-leafed lupin, and more tolerant of brown spot, but narrow-leafed lupin is more responsive to good seasonal conditions and less sensitive to frost. We conclude that yellow lupin has a place in Western Australian farming sys tems on soils with >10 mg/kg extractable [Al] where these soils are in clos e lupin rotations, in areas where brown spot is severe, or in low rainfall areas where narrow-leafed lupin yield potential does not often exceed 1 t/h a on these soils. However, yellow lupin has had relatively little breeding effort in Australia and its place will remain precarious until better adapt ed, higher yielding cultivars become available.