In 1989, funding was provided to establish a large-scale (16-ha), long-term trial at Roseworthy campus. The trial aims to compare organic, biodynamic, integrated, and conventional broadacre farming systems for attributes of sustainability. It is overseen by a 13-member management committee comprising farmers with experience in each practice, agronomists, and soil scientists. Through the monitoring of indicators such as soil physical, chemical, and biological changes, product quality, economics, crop water usage, and energy requirements, the comparative advantages or disadvantages of each system are being evaluated in terms of productivity, profitability, and environmental sustainability. After 6 years, significant differences between systems are apparent in economic returns and soil available phosphorus (P) levels. The biodynamic treatment has the highest gross margins, followed by conventional, organic, and integrated. Conversely, available P levels on the biodynamic and organic treatments have declined 12 and 9%, respectively, since the start of the trial, while both the integrated and conventional treatments have increased soil P levels. In summary, it is too early in the trial to state categorically that any one system is more sustainable than another, although trends are now emerging. Weed management remains the main impediment to high production levels on the organic and biodynamic treatments, while input costs, variable yields, and low returns for grazed pastures are major constraints to high economic returns on the integrated and conventional systems.
Vertical distribution of soil available phosphorus and soil available potassium in the critical zone on the Loess Plateau, China
