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Soil amelioration can boost wheat response to nitrogen
Digging into crop nutrition in modern farming systems
Applied field research in Western Australia is highlighting how soil amelioration can boost wheat’s response to nitrogen fertiliser and lead to higher yields for growers.
The uptake of soil amelioration techniques such as deep ripping, rotary spading, delving and mouldboard ploughing across much of WA’s cropping region has helped tackle soil constraints which act as barriers to productivity. A risk assessment has estimated that soil compaction affects 70% of WA’s cropping area, soil acidity 67% and soil water repellence 53%.
But despite widespread adoption of soil amelioration, less is known about how it can impact crop nutrition. Dr Craig Scanlan, a Senior Research Scientist with the Western Australian Department of Primary Industries and Regional Development (DPIRD), says the results of this field research tell a clear story.
A better understanding of the different responses to fertiliser following amelioration can enable growers and advisors to make better decisions about their nutrient management program in light of their amelioration strategy.
This research is part of a larger crop nutrition collaboration and GRDC investment led by Murdoch University and DPIRD in partnership with The University of Western Australia, Summit Fertilisers and CSBP through the SoilsWest alliance.
Amelioration can shift the response to nitrogen fertiliser
Two locations in the WA wheatbelt, Badgingarra and Tammin, were used as field trial sites for this study. At both, wheat was the only crop sown and nitrogen fertiliser was applied at rates of 0, 40, 80, 120 and 160 kg nitrogen/ha.
At the Badgingarra site, on pale deep sand soil, three different amelioration treatments (rotary spading, delving, and mouldboard ploughing) were tested and compared to a non-ameliorated treatment.
The Badgingarra site was known to have a water repellence constraint. All three amelioration treatments reduced water repellency and showed higher grain yield responses to nitrogen fertiliser in comparison to the non-ameliorated treatment.
Soil amelioration also had a beneficial effect at the second field trial in Tammin. This site is on yellow sand and has a compaction constraint.
The deep ripping amelioration treatment improved the grain yield response to nitrogen fertiliser, which is thought to be due to the crop roots being able to grow better into the subsoil and therefore accessing more nitrogen and water from deeper down in the soil profile.
Where is the nitrogen coming from?
The next phase of this research is investigating whether soil amelioration is enabling crops to access more a) nitrogen from fertiliser, or whether this increased uptake is actually from b) soil-derived nitrogen associated with the mixing effect of amelioration treatments.
To distinguish between the two nitrogen sources, the fertiliser applied contained the labelled nitrogen isotope 15N, which can be separated from unlabelled soil-derived nitrogen.
This experiment has been run over two seasons, meaning that the proportion of fertiliser nitrogen that stayed in the soil to be accessed the following year can be determined.
Although the results emerging so far are preliminary and require further analysis, Dr Scanlan and the project team have discovered some interesting early findings.
A greater amount of fertiliser nitrogen retained in the grain is due to the higher yield response post-amelioration. These early findings also suggest that mixing the soil through amelioration techniques has not limited soil nitrogen supply to the crop.
On soil where there are constraints such as water repellence, improved understanding of nitrogen dynamics emerging from this research can provide greater confidence in the return on investment from nitrogen fertiliser and soil amelioration.
This research is part of the GRDC investment ‘Nutrient re-distribution and availability in ameliorated and cultivated soils in the Western Region (DAW1801-001RTX)’ and is supported through the SoilsWest alliance by DPIRD, Murdoch University, University of Western Australia, Curtin University, CSBP, and Summit Fertilisers.
Contact: Craig Scanlan, Senior Research Scientist, DPIRD and Honorary Research Fellow, Murdoch University. Email: firstname.lastname@example.org
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