Trials established in 2017 in Western Australia’s eastern grainbelt aim to find a cost-effective way of improving and maintaining production on subsoil-constrained sandplain soils in low rainfall areas.
Researchers are investigating the effectiveness of local carbonate sources, as alternatives to traditionally-used coastal lime sand, in reducing subsoil acidity. They are also investigating the effectiveness of deep ripping and cultivation to alleviate subsoil compaction, and their effects on soil acidity.
The trials are being conducted by the WA Department of Primary Industries and Regional Development (DPIRD) as part of the Grains Research and Development Corporation’s (GRDC) five-year investment in the Soil Constraints suite of projects in the western region.
DPIRD senior development officer Caroline Peek said crops in the trial plots which were deep ripped were significantly greener, and had better root systems, during the very dry 2017 growing season and it would be interesting to see if this translated into higher yields.
“Crop plants growing in areas where inclusion plates were used (which help incorporate surface material into the subsoil) also looked better and had significantly stronger roots than plants growing between the areas where plates were used,” she said.
Ms Peek said it was important to address constraints in sandplain soils common in the eastern grainbelt given increasingly variable growing season rainfall and the need to get crop out of the ground from often limited rainfall.
“Most of these soils are naturally low in pH and high in aluminium, and cropping continues to acidify these soils,” she said.
“With the use of heavy agricultural machinery, some of these soils are also prone to subsoil compaction.”
Ms Peek said the continued application over time of a neutralising source such as lime sand had been shown to improve and maintain the productivity of these soils.
“However, many growers in the eastern grainbelt find the transport cost of coastal lime sand to be prohibitive at the rates required,” she said.
“It is also thought that low rainfall in the area may limit the movement of lime sand down the profile into the subsoil – which adds to grower concerns about the time it will take to achieve a return on their lime investment.”
Ms Peek said some growers were interested in mining and applying local neutralising sources which were often associated with subsoils of lower value red calcareous clays.
“Previous research has shown that very fine material reacts more quickly with the soil and that adding inclusion plates to a deep ripper can achieve good results as it helps to ameliorate subsoil compaction and allows some surface material to become incorporated in the subsoil,” she said.
Ms Peek said the trial, which will continue in coming seasons, was being conducted at Kalannie.
The pH levels at the trial site were 4.5-4.8 0-10cm from the soil surface, and 4-4.2 at 40-60cm from the surface, with high levels of aluminium.
Treatments included crushed carbonate rock applied at 4.5 tonnes per hectare and 9t/ha; ‘screened’ carbonate soil applied at 5.5t/ha and 11t/ha; ‘bulk’ carbonate soil applied at 30t/ha; and lime sand applied at 4t/ha.
Deep ripping treatments – tested in combination with the carbonate treatments – included deep ripping to a depth of 50cm, deep ripping with inclusion plates – to a depth of 45cm; and offset discs (cultivation).
The wheat variety sown in the 2017 trial was Scepter sown dry on May 21 2017, followed two days later by rain which triggered germination of the crop.
Ms Peek said the season had been very dry but about 90mm of rainfall was received in August 2017 and September 2017, which would influence the final 2017 trial results.