TRIALS CONDUCTED through the Better Soils Project in SA (see related story left) have demonstrated dramatic yield and growth benefits to ripping sandplain soils and inserting lucerne pellets to break up compaction.
Michael Richards is coordinator of the Southern Yorke Peninsula Alkaline Soils group, which conducted the compaction on-farm trials, among others supported by the project.
"Our trials aimed to identify the effects art crop growth and yield of breaking up subsoil barriers such as stones, compaction layers or highly alkaline subsoil layers."
Testing compaction treatments in sands, growers deep-ripped every 2 metres to a depth of 50 cm and lucerne pellets were inserted into several of the rip lines.
Located at grower Shaun Slater's property 'Berevon', 17 km south-east from Minlaton, these trials identified an increase of 75 per cent in plant growth. By ripping only, an increase of only 50 per cent in plant growth was observed.
"The extra plant growth was spectacular and this year we have installed larger treatments with a multi-tyne ripper," Mr Slater said.
Yield estimates based on hand harvesting showed that the increased growth carried through to increased yields, with ripping and adding pellets increasing yields by more than 30 per cent. Although growers suspect that the actual yield gain over an entire paddock might not be as substantial. Grain weight was also increased - by an estimated 2.6 per cent for a 500 grain sample.
"The rip-only treatment, while showing increased plant growth, had 19 per cent lower yield than the 4.2 tlha yield achieved in the control and also 0.48 per cent lower grain weight," Mr Richards said.
The overall results were encouraging enough for Mr Richards to start ripping and adding lucerne pellets to some of his own sandhill country on 'Ribo'. He says soil pits showed that there was a lot of extra root growth to the depth of the rip lines.
By contrast, in areas that had not been ripped, root growth stopped at 12 cm because of the tendency of pure sand to pack to a density that is more than the 3 megapascals maximum soil strength that roots can grow through.
Mr Richards says the Better Soils Project improved his understanding of how soil properties relate to productivity, and how water moves through the soil.
"The relationship between water movement, root growth and soil compaction was something I had not put together in that way before.
"It became clear that just because the water is there, it does not mean the roots can get to it or even use it, and that was made very clear by the trial results."