Managing Nutrition in Sandy Soils to Close the Yield Gap

Therese McBeath, Bill Davoren, Rick Llewellyn and Willie Shoobridge
Agriculture, CSIRO, Waite Campus, Adelaide.
Peer review: Sean Mason, University of Adelaide

Background
Sandy soil types of the Northern Mallee often underperform despite good weed management and increased inputs of nitrogen and sulphur. There is still a yield gap that can be addressed, with anecdotal evidence of unused water commonly remaining in the soil at depths of approximately 60cm at harvest. In 2014 we set in place a diagnostic procedure to attempt to identify the production limitations on a poor-performing dune at the MSF site near Loxton. Characterisation of the plant available water capacity allowed us to calculate water use efficiency which suggested that the 2014 plots were operating well below industry benchmarks. Penetration resistance was measured to be greater than the threshold predicted to impede root exploration at 20-45 cm depth, suggesting that compaction might be limiting yield. Replicated harvest test strips on and off of wheel tracks measured at three locations in 2014 showed a significant effect of the wheel track compaction at one location only. The site is alkaline sand and pre-sowing soil tests in 2014 indicated relatively low soil test values for sulphur (S) and zinc (Zn). In-season tissue tests indicated marginal status for nitrogen (N), Zn and copper (Cu) and test strips with additional N showed a positive response. The likely primary limitations to production identified were compaction and nutrition.

Key messages
• 40 kg N/ha applied upfront was the best yielding treatment for 2015, with the best protein results where the 40 Kg of N was applied as Urea.
• We found that 20 kg N/ha applied as a Zn enriched Urea product achieved a yield close to 40 kg N/ha as straight urea and we plan to test this treatment again in 2016.
• The timing and form of S application did not have any effect in 2015.