According to the 2020 Annual Results Report of the Ripper Gauge project of the Grain Research and Development Corporation (GRDC) no clear method of soil amelioration consistently gives a higher grain yield.
Soil amelioration is a key part of farming systems in Western Australia to overcome soil limitations to crop production. While there is a good network of demonstration sites established across the port zones of WA, there are many soil types where the benefit and longevity of soil amelioration practices are unknown.
Benefit of soil amelioration
The Ripper Gauge Project aims to demonstrate the benefit of soil amelioration across a wider range of soil types that are common to the grain growing region in the state, with twenty demonstration sites being established across five port zones in 2018.
The range of crops grown in the 2018 and 2019 seasons by the host growers were cereal dominant (wheat or barley). There were a few instances where canola, lupin, or hay were grown.
The soil types tested in this project range from loamy sands through to gravel and sand duplexes, forest gravels, and clay soil types. Each site was selected based on the low amount of knowledge available on how they will respond to each soil amelioration practice. Three standard treatments were tested against a control (no amelioration) at each site, including ripping to 30cm, ripping to 60cm, and a solution or combination of methods to address local soil constraints.
While increases in grain yield in 2018 from soil amelioration treatments were generally soil type specific, grain yield responses in 2019 were more variable, the GRDC-report says.
Clay-based soil types
For the soil types that were generally described as having a high clay component, there was small change in grain yield of about 0.3 ton per hectare across most sites compared to the 2018 season, where there was a 0.1 t/ha to 1.2 t/ha increase observed.
According to the report ripping to 60 cm depth on clay soil did give a grain yield benefit at one site but was similar or lower than the 30 cm ripping treatment at all other clay soil type locations, where there was a comparison. The addition of grower investigated treatments where alternative or multiple soil amelioration practices were used were less effective than the ripping treatments in 2019, despite some sites showing promise in the 2018 season.
Gravel soil types
There was at least one soil amelioration treatment that gave an increase in grain yield at the sites where the soil type was generally described as having a significant gravel component, the report points out. The grain yield benefit for all soil amelioration treatments ranged between -0.7 t/ha and 0.7 t/ha across all sites in this subgroup. This was similar to the variation observed in 2018.
A Soil-Science Revolution Upends Plans to Fight Climate Change
The maximum tillage treatment in 2018 – at selected sites – led to the highest or equal highest grain yield at the site, but this was not sustained for the 2019 season. It is likely that the benefit of maximum tillage being evident in the first year only was due to a ‘tillage effect’, where soil that is cultivated has an increased mineralisation rate of nutrients and greater exploration by crop roots.
Loam type soils
There was only one site where there was an increase in grain yield in the subgroup of soil types that were generally described as loam based in 2019. The Hines hill site was fallowed in 2018 to allow for sufficient soil moisture and reduced soil strength to be able to complete the ripping treatments in September of 2018. Ripping to either 30 cm or 60 cm led to a near doubling of grain yield at the Hines Hill site, with the application of Morrell lime not increasing grain yield any further.
The increased germination of weeds following tillage events that greatly disturb the soil was noted at many sites following the implementation of soil amelioration treatments at the start of 2018, although this was not captured in site observations. Dry conditions at Yuna and Morawa reduced the yield potential of crops in these regions, and this led to low grain yield and very little difference between soil amelioration treatments.
Sandy soil types
The study also evaluated two sand soil types that are not normally considered for ripping due to lower fertility or the presence of subsoil constraints. While there was an increase of up to 0.7 t/ha of grain yield from soil amelioration treatments in 2018 at the Kurrenkutten site, there was little difference in grain yield for the 2019 season. This lack of response from soil amelioration treatments is most likely due to a poor season experience in 2019, as barley was grown at the site in both years with similar agronomic inputs.
The GRDC-report says there was a positive economic benefit to soil amelioration activities for 46% of soil amelioration treatments imposed across all sites. The economic benefit includes an initial cost of -$ 80 per hectare to represent the average cost of imposing any soil amelioration treatment.
There were only 10 out of 66 treatments that returned an economic benefit of greater than $ 100 per hectare in total from two production years across all sites. This is most likely due to the very small increases in grain yield that have been observed for most soil amelioration treatments across all sites in this study. Seasonal conditions (average annual and growing season rainfall) have been variable within and between years and between sites in this study.
A third year of data to identify multi-seasonal trends will enable a clearer view of the benefit of each soil amelioration activity over time, according to the GRDC-report. Greater definition of what constitutes success is also required to enable the results of this project to be interpreted. For example, a soil amelioration activity may be deemed successful if there is an economical return in 2 out of 3 years. In this case, a large positive return in year three of this study may make many soil amelioration options viable for growers to adopt.
