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 dryland 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 compositions of a ley pasture will affect subsequent cereal yields and profitability. An analysis of the 1965-89 record reveals that 43% of the variance in wheat yield can be accounted for by the equation: WY = 3.42 + 0.0165AOR - 0.0000165AOR2 + 0.12PL - 2.64PG + 0.39PG2 = 0.019PG3 were WY is wheat yield (t/ha), AOR is April-October rainfall in the whet year (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 with other published data, our results support the claim that nitrogen from legume sources is economically more efficient than fertiliser nitrogen, but the largest effect of increasing legume content comets from avoiding yield loss associated with grassy pastures.