Digging deep to maximise sowing opportunities and wheat establishment. (On-farm testing of long-coleoptile wheat genotypes and sowing depth)

Overall Objective

Early sowing has the potential to increase wheat yields across WA. However, early sowing relies on sowing opportunities determined by rainfall or the use of early sowing. Dry sowing is now widespread in WA as a means of establishing cropping programs early. Increased summer rainfall means that there is often stored soil moisture at depth. Deep sowing into this stored soil moisture has the potential to enable early establishment. Current wheat varieties have short coleoptiles which limits their sowing depth to ~5cm. CSIRO has developed long-coleoptile genotypes that allow emergence from sowing of 120mm or deeper. We estimate that long coleoptile wheat genotypes could increase wheat yield by 40% when paired with deep sowing (Rebetzke et al. 2007).

Our project aims to test the emergence of long coleoptile wheat from deep sowing in WA and provide a value proposition for including long-coleoptile genetics in new wheat varieties.

Project Synopsis

Increasing summer rainfall and a growing appreciation of the importance of early establishment to maximise wheat yield potential have led to interest in deep sowing of wheat into stored soil moisture.

Unfortunately, current commercial wheat varieties utilise dwarfing genes that limit coleoptile length, and they are therefore limited to sowing depths shallower than 5cm. Long coleoptile wheat varieties that utilise alternate dwarfing genes (Rht13 and Rht18) have been proposed as a genetic solution to allow deeper sowing into stored soil moisture.

The aim of this project was to assess the emergence of new long coleoptile wheat genotypes from deep sowing on farm using farmer’s equipment. The project also aimed to investigate if drone imagery with NDVI could be used to assess differences in wheat emergence and plant establishment in these experiments.

Six experiments were carried out over 2 years (2021 and 2022) in the Eastern wheatbelt of WA. Achieved sowing depths for the deep-sown treatments ranged from 80 to 135mm. The benefit of the long coleoptile wheat variety was not obvious at all sites. There was only benefit from the long coleoptile trait in terms of emergence at two sites, Muntadgin and Merredin in 2022. These were two sites where the deepest sowing was achieved (greater than 120mm). At other sites, sowing was too shallow or delayed so that the deep sowing treatments could not realise genetic differences in coleoptile length.

We also showed at sites where there were large differences in plant emergence that it was possible to monitor differences in plant establishment using drone imagery. Measurements of NDVI clearly showed at these experiments that when sown deep the long coleoptile wheat trait was better able to establish ground cover than commercial shorter coleoptile length varieties.

The experiments showed that the long coleoptile wheat trait assures wheat establishment with deep sowing. However, the benefits of long coleoptiles were not obvious when sowing was less than 100mm or when sowing was delayed. The project highlighted the difficulties in conducting sowing time/sowing depth research using farmer’s equipment. Seeding time is a particularly important and busy time of the season for growers. This type of on-farm research can disrupt sowing logistics. Therefore, it was difficult to ensure crops were sown on time. Furthermore, current sowing machinery is limited in the sowing depths that can be achieved.

Future research should focus on small plot research to establish confidence for farmers to sow these new genotypes deep. Future research should also focus on understanding the interaction between sowing depth and temperature with respect to these new long coleoptile wheat genetics. We also propose that future research should focus on other aspects of agronomy that fit alongside sowing depth and can realise the success of wheat establishment when deep sowing (e.g. fertiliser use and herbicide use).