Comments
The soil at the Latham site is referred to as an acid Wodjil, brown sand with increasing gravel with depth. These soils were naturally highly acidic before agriculture. Both exchangeable aluminium and acidity levels increase with depth (table 1). The poor production from this paddock means that it is not cropped every year and often left to volunteer pasture. It was pasture in 2014 and cropped in 2015.
In 2015, the year of the demonstration, wheat yield was not significantly influenced by lime or incorporation (figure 2).
There is a soil compaction layer peaking at 30cm, though roots are impeded from 10cm (figure 1). Both deep ripping and large offset disc disrupted this layer though no post ripping measurements were taken. Acidity, and the likely aluminium toxicity, are the major constraints at this site. Breaking the compaction layer did little to improve the yield.
Emergence was heavily influenced by the incorporation method. Plants in the Grizzly 36" offset were a week behind the remainder of the trial in emergence. Grizzly Tiny® plots were sown deeper and had significantly less plants/m2 which negatively influenced yield for this treatment. The topsoil became toxic, and slowed emergence, with acid sub-surface brought up by the large offset disc. Surface crusting of the offset disc treatments further detracted from the number of plants emerging. The plants within these treatments went on to tiller very well, with large head size, though not sufficiently to make up yield lost to low plant numbers (Table 2).
There is limited soil movement, therefore limited incorporation, from the Deep Rip and Cultivator point treatments (figure 3). Only small levels of lime incorporation are expected with the current set up of these implements. It is possible to modify the deep ripper to incorporate topsoil to depth, in a narrow band, by adding opener plates behind the tine (refer to work of Isbister and Blackwell, SEPWA newsletter issue 74, June 2015 page 18).
The large offset disc has moved a lot of soil to a depth of approximately 23cm. Bringing acidity to the surface and burying lime to depth. It is likely to have the greatest influence on sub-surface pH into the future. Precision Soil Tech tested the soils and recommended 6t/ha of lime to rectify the soil acidity issues. We speculate that these plots will be the highest yielding plots in future years.
Acknowledgements
Thanks to Wes Benton and Chad McKay, for managing the trial; also to DAFWA technical services staff for their assistance and SoilTech for soil sampling.
This project is supported by the Northern Agricultural Catchments Council, through funding from the Australian Government’s National Landcare Programme.