Identifying opportunities to integrate a spring-sown summer crop into winter wheat-based cropping system in WA

Overall Objective

This project aims to determine the potential to introduce soybean as a new crop option for WA growers to improve the productivity and profitability of cropping systems, and identify how best to fit soybean into current winter cereal-based cropping systems.

A combination of field experiment and simulation modelling was used to test the responses of soybean development, growth and yield to climate conditions in the wheatbelt of WA. A 2-year trial was conducted near Mingenew with first year trial sown in spring with two sowing dates and five cultivars. The second year trial was sown in winter with two cultivars and spring with five cultivars. The APSIM model was tested with trial data and then long-term simulations were conducted at 4 representative locations.

The project demonstrated that there was a potential to adopt soybeans in WA as a cash crop. Both trial and modelling simulations showed that there was an opportunity to sow soybean in winter in the northern wheatbelt of WA. In this part of the wheatbelt, sowing a soybean crop in winter could achieve comparable yield and profit to winter wheat. Due to limited rainfall during late spring and summer in the northern wheatbelt, the opportunity to sow a soybean crop after spring is limited. The simulation results showed that a soybean crop could be sown in either winter and spring in the frost-free high rainfall zone of the southern wheatbelt of WA. There was very limited opportunity to sow a soybean crop in the other rainfall zone of this part of the wheatbelt due to low temperature in winter and low rainfall after spring. Considering that this research project was conducted with a limited temporal and spatial scale of field experiment, which is not sufficient to test the model performance, more field and modelling research needs to be undertaken to confirm the suitable area of adopting soybeans and identify management practices.

Model simulation results demonstrated that soybean would serve as a good break crop. Subsequent wheat yield benefited from soybean as a result of available soil N fixed by legume soybean. We also demonstrated that the rotation of wheat and soybean had potential to enhance economic viability and improve soil nutrients. Integration of soybean into cereal-based cropping system would enhance the diversity of crop rotations, increasing the sustainability of cropping systems. More research needs to be undertaken to identify the rotation pattern of wheat and soybean to better use the climate conditions.

Project Synopsis

Both trial results and simulations showed that there was a potential for soybean to be adopted in WA as a cash crop, and a high-quality feed source. In the warm high rainfall zone of the wheatbelt, it was possible for soybeans to be sown in winter. In warm medium rainfall zone, soybeans could be adopted as an opportunity crop to sow in winter. The results are inspiring in addressing solutions to tackle climate change. Sowing a species which has traditionally been considered a summer crop in winter might be a practical management option for growers to adapt their cropping systems to climate warming. This research provides a foundation for further study which could explore optimal management options for this crop. In the high rainfall zone of the southern wheatbelt, soybeans could be sown in spring. Results which showed that it was possible to sow soybean in winter in the cool high rainfall zone need to be interpreted with caution as frost was not considered in this study. Soybean could serve as a good break crop in WA farming systems since we showed a benefit to wheat yield in crops that followed soybean in the high rainfall wheatbelt region. Growing soybean in a well-planned rotation pattern with wheat in WA would provide potential advantages in terms of enhancing crop productivity/profit, enhancing crop diversity, reducing pest and diseases and fertilizer application and mitigating some of the losses associated with climate warming.

Paper presented at the 2024 Agronomy Conference in Albany.