The report discusses the important findings and conclusions of the GRDC Irrigated Wheat Evaluation Project, conducted from 2001 to 2005. It highlights a range of factors that could contribute to building a crop structure (ie canopy management) necessary for achieving high grain yields with reduced lodging risk, and with best use of solar energy (growth), residual and fertiliser nitrogen, and available water.
The project’s conclusions have been summarised in the guidelines below:
Choice of variety:
- Short season varieties were most efficient with nitrogen and water,
- Flowering early within the 3-week optimum period around 1 October can save one irrigation for similar yields,
- Stem strength and anchorage of varieties is highly dependent on management.
- Soil conditions should allow good root growth for plant anchorage, being well aerated, with good organic carbon content, no hard pans, minimum tillage, well managed traffic,
- Deep sowing (6-7 cm) will enhance strength of plant anchorage,
- Lower sowing rates for wider row-spacing, to attain a within-row plant distance of at least 2.5 cm, will achieve best anchorage strength,
- Plant densities of 60 to 80/m2 will minimise lodging losses while maintaining high yields.
- Limited early growth, restricted tillering and delayed canopy closure, resulting in ground cover at Z30 (start stem elongation, Zadoks crop growth stages, see Appendix 1) of less than 70%, will enhance stem strength and better the balance between “source” size (leaves, stems) and “sink” numbers (spike, kernels); with a shoot density target of 600-800 shoots/m2 at Z30,
- Nitrogen fertiliser application to promote yield is most efficient when topdressing is between Z30 and Z32 (see Appendix 1),
- First spring irrigation during early stem elongation is important, when required, if high yield potential has been set,
- Topdressing near flowering with 30-40 kg N/ha can increase grain protein by 0.5-1% and yield with 0-0.5 t/ha, if there has been an earlier topdressing for yield,
- Green leaf area at flowering needs to be more than 3.5 green leaves per shoot to achieve greater than 8 t/ha yield,
- Green leaf area duration is maximised with timely irrigation after flowering to fill the “sink” to potential.
These guidelines seem valid under irrigation on the plains of southeastern Australia. There are no recipes to secure consistently high yields and a key message in striving for high yielding crops is that you can’t manage what you don’t measure. Crop knowledge and monitoring are important to achieving profitable results as described here and in the separate feature about monitoring. TOPCROP monitoring can be used to learn more about crop-soil- environment interactions.
The factors presented can be used with key checks for best management practice in Wheatcheck to determine with one’s own experience local guidelines for efficient use of resources in high yielding grain production, which of course will be dependent on the availability of water. Comprehensive management guidelines for growing eight tonnes a hectare using many of the recommendations from this study have been described by John Lacy and Kirstie Giblin
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Wheatcheck Recommendations, 2003, NSW DPI, Vic DPI, GRDC, ICF.
NSW DPI Primefact 197, 2006