Conservation agriculture (no-till) cropping systems is considered by many to have improved soil health, timeliness of sowing, moisture conservation and resulted in higher grain yields. The key components of this system are full crop residue (stubble) retention, diverse rotations and minimal soil disturbance. However the recommendation for full residue retention is sometimes seen as a major constraint to the adoption of no-till, and increasingly the use of tillage to combat herbicide resistant weeds or non-wetting is employed by growers.

Dr Ken Flower (The University of Western Australia), in partnership with the Western Australian No-Tillage Farmers Association (WANTFA) and CSIRO, leads a long term research site established in 2006 at Cunderdin on an alkaline red sandy clay loam. The experiment which has co-investment from the Grains Research and Development Corporation (GRDC) aimed to determine the long term benefits of the key components of conservation agriculture and has shown that significant amounts of residue can build up through the removal of livestock from the system and no removal or burning of stubble. Using four different cropping philosophies i) cereal rotation, ii) diverse rotation, iii) control (monoculture wheat) and iv) ‘farmer’ rotation (cereal, cereal, break crop or fallow), a total of 11 crop sequences were established; and from 2010 a subset of plots had residue retained and spread behind harvester or were wind-rowed behind the harvester and burned, to consider the impact of stubble load on production.

Wind-rowing and burning were effective at decreasing residue levels by 40 to 60 per cent, with a variable influence on grain yield observed depending on crop residue type and amount. When there was relatively little cereal residue present after harvest (less than about 3 t/ha), retaining all the residue resulted in yield gains compared to where residues were reduced by wind-row burning; whereas, the opposite was true under greater stubble loads with higher yields from windrow burning.  By contrast, the effect of windrow burning of canola residue on the following wheat yield was small regardless of high residue levels.

Continuous wheat and the cereal rotation had the highest cumulative nine year average gross margins, despite higher grain protein and improving yields under a more diverse rotation. Lower gross margins in the diverse rotation were associated with poor legume performance in many years and low canola yields in dry seasons. Improving the reliability of these break crops in this growing environment is the key to increasing their uptake by farmers. Cover crops in the rotation generally negatively impacted gross margins.

At this relatively low rainfall site, with Mediterranean-type conditions, in south-western Western Australia, highest profitability came from having moderate residue amounts, in a rotation dominated by cereals and not including cover crops. The experiment will continue to inform longer term outcomes for production, weeds diseases and soil health. A recent publication can be found here. For further information please contact Dr Ken Flower ([email protected]).

Image: Burnt windrow after Canola. Image attribution: Ken Flower, University of Western Australia