EFFECT OF LUPINS AND PASTURE ON SOIL ACIDIFICATION AND FERTILITY IN WESTERN-AUSTRALIA

An 'across the fence' comparison of farmer paddocks with nearby vir-in bush sites was made at 3 locations, to measure the effects of lupins and subterranean clover based pastures on the chemical properties of the soil. Estimated rates of acidification in the 0-60 cm depth were 0.29-0.55 kmol H+/ha.year for wheat-lupin paddocks and 0.16-0.21 kmol H+/ha.year for pasture paddocks. A significant proportion of this acidification occurred below 20 cm, particularly in the lupin paddocks (up to 70% of the total). Severe water repellency had developed at 1 location that had produced 30 lupin crops with the occasional wheat crop. Despite these detrimental effects, lupins maintained soil mineral nitrogen and organic matter contents and electrical conductivities similar to those in pasture paddocks, even though the soils in the lupin rotations had been sown to wheat more frequently.