EFFECTS OF ANNUAL PASTURE COMPOSITION ON SUBSEQUENT WHEAT YIELDS IN THE WAITE PERMANENT ROTATION TRIAL, SOUTH AUSTRALIA

Legume-based annual pastures are commonplace in southern Australian dr yland farming systems. By using the long-term wheat and pasture yield records from the Waite Permanent Rotation Trial (established in 1925), we have quantified how changes in the production and composition of a ley pasture will affect subsequent cereal yields and profitability. A n analysis of the 1965-89 record reveals that 43% of the variance in w heat yield can be accounted for by the equation: WY = 3.42 + 0.0165AOR - 0.0000165AOR(2) + 0.12PL - 2.64PG + 0.39PG(2) - 0.019PG(3) where WY is wheat yield (t/ha), AOR is April-October rainfall in the wheat yea r (mm), PL is pasture legume yield in the preceding year (t/ha) and PG is pasture grass yield in the preceding year (t/ha). By comparison wi th other published data, our results support the claim that nitrogen f rom legume sources is economically more efficient than fertiliser nitr ogen, but the largest effect of increasing legume content comes from a voiding yield loss associated with grassy pastures.