The run of dry years has got farmers thinking about the value of ameliorating issues related to sandy soils.   Demonstrations and trials conducted through the Sandy Soils project has helped clarify the value of these treatments on different soils in different rainfall zones. 

Clay spreading has been shown to be beneficial in assisting in weed control, improving crop germination and in addressing wind erosion.  However, heavy rates of clay (over 200t/ha) have appeared to reduce plant available water with negative results in dry seasons.  Also, the use of clay with high levels of carbonate has resulted in manganese deficiency that is often worse in dry seasons. Apart from these situations farmers who have spread clay are generally happy with the results.

Delving appears to be an even more positive story.  Trials and demonstrations this year at Parilla, Monarto and Waitpinga clearly demonstrate significant increases (200-300%) in dry matter production along delved lines compared to clayed and unclayed areas. This is consistent with observations in previous dry years and is expected to provide significant yield increases.  It is also becoming clearer that the modification of the subsoil is at least as important as addressing issues in the topsoil.  The “ideal” delving technique should therefore be conducted using machines with tines at less than 1 metre spacing, aiming to bring 80-120t/ha of clay to the surface and also having the capacity to modify the subsoil through depositing clay in bleached layers and/or mixing surface soils deeper in the profile.
 
Questions about the benefits of deep ripping of soils and how long they last have seemed to be around for ever with results varying depending on soil type, ripping methodology and subsequent management.  Sandy soils are providing a similar story. 

Siliceous sands (usually white and grey sands) on Eyre Peninsula have provided some responses to ripping in dry years but not in “average” rainfall years.  This supports work conducted by the EP Farming Systems project where over a 5 year period ripping of sands near Wharminda generally only provided significant yield increases in dry years.  Ripping of siliceous sands on Kangaroo Island also did not provide significant responses although ripping with additional nutrition at depth did result in yield increases at both locations.  This year ripping conducted on siliceous sands in the Mallee has resulted in higher dry matter levels.   However, ripping of clayed, siliceous sand at Waitpinga has not provided large responses.  Ripping of “red” sands near Bute in 2005 did result in yield increases and appears to have provided a residual benefit with visual differences between treatments apparent this year.  The bottom line appears to be that unless there is a clear compaction layer (as found at Bute) the response to ripping of sands varies considerably and (particularly on white/grey sands) should not be undertaken on a broadacre scale without some previous investigation.

These and other techniques addressing issues affecting production on sands will be highlighted at displays at the Paskeville Field Days.  Look for the Bureau Logo.

AUTHOR: David Davenport, Soil and Land Management Consultant, Rural Solutions SA

CONTACT: David Davenport, Rural Solutions SA Pt Lincoln Office, Telephone 8688 3404, Mobile 0427 201 956, davenport.david@saugov.sa.gov.au