Fertiliser placement with the seed at depth has the potential to caused toxicity, leading to reduced emergence and coleoptile stunting, particularly in hostile soil conditions and with compound fertilisers. Deep sowing could also be achieved by switching seed and fertiliser outputs; however, this has the potential to cause variable seed placement and may require the knifepoint to rip excessively deep.

Pushing the limits of early, deep sowing

2024 trials measuring temperature, depth and moisture at depth found seeds were able to germinate and emerge where there was a minimum of 40 mm of moist soil above seed, and temperature around seeds did not exceed 26 degrees Celsius. At Kalannie (72 mm rainfall Jan-March), wheat sown deep into stored moisture failed to emerge from 110 mm below the bottom of the furrow, subject to 28-degree soil temperatures at depth and 30-40 mm of moisture above seed. All other trials that had 60-100 mm of rainfall between January-March, with soil moisture starting 65-85 mm below the ground’s surface. These locations had soil temperatures between 23-26 degrees Celsius and overall had similar, sufficient soil moisture at depth for wheat emergence, sustaining plants until germinating rainfall occurred 2-4 weeks after seeding.

Temperatures recorded 110 mm below the furrow had significantly less fluctuation than 40 mm readings. Warmer soil temperatures reduced coleoptile growth from potential maximum lengths, particularly shorter coleoptile varieties Mace and Scepter. There was a positive correlation between cooler temperatures, coleoptile length and emergence from 110 mm sowing depth.

Wheat that took longer to emerge was at the risk of furrow infill leading to increased soil strength from rainfall in the days/weeks following sowing. Rainfall doubled soil strength readings for deep sown furrows and significantly reduced emergence potential of short coleoptile varieties.

Figure 1. Soil furrow fill saw seeds emergence through 120 mm of soil in Dowerin. Plants per meter of row 12, 21, 28 and 68 days after sowing (DA-A = Days after application). Long coleoptile varieties Mace-18 and Magenta-13 faster emergence with higher total populations established than shorter coleoptile wheat.

Fertiliser placement

Compound fertiliser placed with seed at 60% rate reduced plant emergence from depth regardless of variety at multiple trial locations. Shallow sown wheat was lesser affected. There was no observed reduction in emergence and early biomass reduction with the fertiliser placed 40-50 mm above the seed when sowing deep or conventionally. Uniform treated fertiliser also did not significantly impact wheat establishment where sown at 110 mm compared to untreated fertiliser.

Figure 2.Plants counts per meter row at 11, 20, 27 and 67 days after sowing for deep sown wheat into moisture, and shallow dry sown wheat.

Fungicide and disease

Disease trials conducted in 2023-2024 found more significant responses to root disease control with various fungicides when sowing shallow compared to deep. Various trials since 2021 have found rhizoctonia root infection incidence to be higher for untreated wheat, and for roots growing in the top 10 cm of soil. Treatments with Uniform had little to no rhizoctonia symptoms regardless of depth.

In 2023 and 2024 the results have suggested fungicide seed treatment products containing ipconazole, metalaxyl, cyclobutrifluram, priothioconazole and penflufen had negligible effects on emergence of long coleoptile wheat sown at depth. In some instances, seed treatments have increased coleoptile extension compared to the untreated control where there is increased soil borne incidence. Predicta B readings across multiple sites and years found a trend for increased numbers and prevalences of different soil borne pathogens found in the 0-10 cm compared to the 10-30 cm profile.

Herbicide tolerance

Overall, long coleoptile wheat sown 100 mm had equivalent emergence across 8 pre-emergent herbicides, while 35 mm sown wheat had reduced emergence from trifluralin, flumioxazin + terbuthylazine, and cinmethylin applied at tolerance rates (2024 tolerance trial). There was no significant difference in emergence at label rates between 35- and 100-mm sowing depths (2022, 2023 tolerance trials).

More soluble herbicides with label depth warning (e.g. cinmethylin and metribuzin) had more plants emerged and were higher yielding when deep sown, compared to conventional depth. Early post emergence, soluble & weaky binding herbicides that diluted in soils had lesser impacts on shallow wheat did compared to herbicides that remained in topsoils, e.g. trifluralin.

Deep sown wheat had biomass reductions due to upper nodal roots being subject to growth restrictions in topsoil containing herbicides, particularly for low solubility herbicides remaining in top 10 cm (e.g. flumioxazin, terbuthylazine, pyroxasulfone, trifluralin). Biomass relative to UTC was reduced for 35 mm wheat than 100 mm across most treatments. Phytotoxicity was more prominent and longer persisting for 35 mm than 100 mm sown Mace-18 wheat (2023, 2024 findings).

Results have also shown weed competition from highly vigorous, fast growing long coleoptile wheat varieties, particularly when wheat germination occurs at depth prior to topsoil residing weed seeds.

Conclusion

The national project will continue exploring various aspects around management, environment and genetics of new long coleoptile wheat lines in order to aid in grower adoption. With the continued exploration of these new genetics and sowing techniques, the long coleoptile wheat project paves the way for more sustainable and efficient wheat farming systems in Australia, ultimately enhancing productivity and resilience to changing climate conditions. Further research and adoption of these findings will contribute to improving yields and farm sustainability in the coming years.

Acknowledgments

Dr. Greg Rebetzke and CSIRO for coordinating the project, and his support within past and current projects. SLR would also like to thank all other researchers involved within the national project.

The research undertaken as part of this project is made possible by the significant contributions of growers through both trial cooperation and the support of the GRDC, the author would like to thank them for their continued support.

Contact details

Michael Lamond,

SLR Agriculture

148 Avon Terrace York WA 6302

michael.lamond@slragriculture.com.au