Agricultural productivity growth has been strong relative to other sectors in the Australian economy, and relative to the agricultural sectors of other developed countries. However, as commonly observed among other developed economies, growth in productivity in the broadacre sector of Australian agriculture seems to have slowed in the past decade. This paper uses the adjusted cumulative sum square (CUSQ) index to examine the trend stability of total factor productivity in Australian broadacre agriculture over the period 1952-53 to 2006-07. The results show that a significant slowdown occurred around the mid-1990s. Further analysis shows that the slowdown in productivity growth is driven by a longterm decline in public R&D investment in addition to poor seasonal conditions in the past decade.