Farrer Centre Research Report 1998

Project Summary:
Despite the acknowledged benefits to soil protection and fertility, adoption of stubble retention has been slow and concerns over crop performance have led some farmers to abandon the practice. A recent review of long term field trials revealed that stubble retention consistently reduced average wheat yields by 0.3 t/ha in southern NSW. Allelopathic effects of the residues are often suspected to cause reduced yield, but there have been few quantitative studies conducted under field conditions using actual crop stubbles. Farmers require rules of thumb based on stubble type, quantity and degree of decomposition to assess the allelopathy risk to subsequent crops.

This project will screen a range of crop species and varieties and assess the allelopathic potential of their residues including effects of stubble quantity and degree of decomposition. These effects will then be evaluated in relation to the other effects of the residue such as water conservation, disease carry-over and N tie-up. The project will include collaboration with scientists in Kiel (Germany) where allelopathy in cropping systems is an area of current research. Rules of thumb for stubble management will be developed from the research for incorporation into crop monitoring programs such as TopCrop. These rules of thumb will benefit the grains industry by reducing the yield loss caused by stubble retention in years of high allelopathy risk, and by reducing soil degradation by encouraging retention in years of low allelopathy risks.