Trends in wheat yields and soil organic carbon in the Permanent Rotation Trial at the Waite Agricultural Research Institute, South Australia

摘要: The Permanent Rotation Trial at the Waite Agricultural Research Institute in South Australia was established on a red-brown earth 1925, with predominately cereal-long fallow rotations 34 adjacent plots. trial upgraded 1948 to include greater proportion of pasture leys and currently contains 11 treatments. is unreplicated; however, each phase sequence represented year. Seven original have remained an unbroken since 1925: continuous wheat (W), wheat-fallow (WF), wheat-peas (WPe), wheat-pasture-fallow (WPaF), wheatoats- (WOF), wheat-barley-peas (WBPe), wheat-oats-pasture-fallow (WOPaF). For rotations, soil organic carbon (SOC) top 10 cm declined from 2.75% 1925 mean value 1.56% 1993. One plot, which had reverted permanent 1950, showed smallest decline SOC content 2.46% greatest declines were 4 that included phases (mean 1.22%). In WF rotation 2.75 1.04% during 68 years cropping. Associated yield decreases treatment could not sustain production. Soil C linearly increasing frequency fallows decreasing rotations. Average grain yields (1925-93) 7 sequences ranged 2.64 t/ha WOPaF 0.89 W plot. linear for WBPe, WPaF, WPe, WOF treatments indicate convergence 1990s under current management, average 1.54 1993 1.32%. We hypothesise gradual increase plot 1960s result build-up light fraction material, assists maintainence structure nutrient availability.