ROTATION EFFECTS ON SUSTAINABILITY OF CROP PRODUCTION - THE GLEN-INNES ROTATION EXPERIMENT

This study, which commenced in 1921, is the longest running crop rotat ion experiment in the summer rainfall region of Australia. The 7 rotat ion treatments comprise various frequencies and combinations of maize and spring oat crops with and without autumn oats and red clover ley. The maize and oat yields are analysed separately using principles desc ribed by Paterson (1964). Spline regressions are used to describe the trends of yields with time and to make comparisons amongst the rotatio ns. Yield performance of maize and oats was improved as legume ley dur ation increased, although as maize cropping became more frequent this effect was reduced. Autumn-sown oats benefited both maize and spring o at yields, independent of the presence of a legume ley. Crop yields we re generally maintained in those rotations containing a grazed clover ley. After alteration of ley management in the mid 1960s so that clove r crops were subsequently removed as hay, crop yields in these rotatio ns declined. The benefits of clover ley to crop productivity were cons idered to be primarily due to the maintenance of those soil chemical, physical, and biological properties associated with sustainable crop p roduction.