Stubble management in the high rainfall zone

Project background:

Stubble management is a significant issue in Western Australia particularly in the high rainfall zone, where it is not uncommon for cereal grain yields to reach over 7 t/ha with the resulting stubble loads being up to 10 t/ha. This is a high amount of stubble residue left post harvest and is an increasing concern for local growers due to poor establishment of following crops, nitrogen (N) tie-up, disease carryover issues, and seeding operation inefficiencies such as blockages, hair pinning, poor soil throw, and bulldozing. As a result, plant establishment has become increasingly difficult, particularly in Canola.

Previous GRDC research has been conducted to understand the additional N requirements needed to overcome early N immobilisation by stubble. This research suggests that an additional 5-6 kg N/t of cereal residue can help overcome the issues of stubble N immobilisation. Investigation into whether the addition of nutrients, in addition to an enzyme ‘digester,’ to stubble in conjunction with mechanical stubble treatments during the summer fallow period, can increase the rate of stubble breakdown to allow for improved winter crop establishment (especially canola) and reduction in early season nitrogen tie-up. Reduced carryover of stubble-borne diseases could also be explored via observations.

Broadly, this project will pilot the effectiveness of stubble management/break-down options (chemical and mechanical) in the Albany port zone and assess how these treatments impact on soil nitrogen ‘tie-up’ and establishment of the following winter crops.

To achieve this, two small plot trial sites and three farm scale trial sites have been established in early 2025 in the Albany Port zone. The trial sites will be used to collect scientifically robust data on what treatments effectively manage the high stubble loads commonly faced by farmers in the high rainfall zone of the Albany Port Zone. The project will run from Autumn 2025 through until Autumn 2026.