Stacking Soil Amelioration & Amendments Crop Walk - Farmer Summary
By Kate Parker, WMG Project Officer
Introduction
The West Midlands Group held another crop walk and farmer discussion event on 21st August at the Wathingarra Rd stacking soil amendments and amelioration long term trial site hosted by Jeremy Roberts.
The event was based around discussing stacking soil amelioration methods and novel soil amendments, past trial results from the site and future plans, along with the potential of practical implementation to improve soil health and carbon.
Attendance was sparked by interest in the next steps in soil amelioration, seeing in-field evidence of the effects on soil health by combining soil amelioration and amendments.
The following farmer summary is a collection of synthesised notes taken over the course of the crop walk intended as a refresher for those that were present on the day, and for those that were unable to make the event.
Site Description
The site is located near Badgingarra, on Wathingarra Rd. Site host Jeremy Roberts provided some historical details of the site, noting the land was first cleared and developed in the 1960s. Since then it has gone through a cycle of cropping and pasture phases with a cropping phase prior to the start of the trial in 2021. The site has naturally relatively low pH and has been limed at 6t while in the cropping phase. It has high levels of soil water repellence and the location has high winds, contributing to a proneness to wind erosion.
The initial trial began in 2021 with amelioration treatments (mouldboard plough, rotary spade, shallow tillage and control) being implemented alongside amendments (compost, zeolite, clay, ironman gypsum, compost + clay and control); A second round of amendment treatments were implemented in 2022 (Biochar + Frass). The two main focus points of the site are the interaction of soil amelioration methods with novel soil amendments and the ability to build soil carbon over time.
The site has been sown to lupin (post-trial), wheat (post-trial), wheat, wheat, serradella and regenerated serradella across 2019-2024 respectively. An increase in biomass produced from serradella has been observed this year in line with the higher rainfall recorded comparatively to last year.
Amendments
Compost
The compost used in this trial was C-Wise ‘Humicarb’, the most humidified and processed of the C Wise composts – taking a 6 month process, and was distributed at 15t/ha. The group discussed different types of compost and wanted to understand how each of these work, with valuable input being provided by C-Wise’s Chris Wieman. Costs also came under the spotlight with some suggesting that broadacre use would suit a low cost option due to freight being a large portion of expense.
Attendees also questioned how you would get the aeration to the compost to keep it alive and working well. Suggestions centered around the use of deep rooted species and of a method from South Africa – vertical plowing, a ‘heaver’ or ‘subsoiler’ that has a shattering effect. General consensus was that when using compost, incorporation is a vital aspect.
Out of all treatments, the compost is edging a little ahead with each season, however there needs to be more research into this. The group discussed that there is definitely something there (possibly due to micro activity having additive benefits) but we need to figure out the right type, application rate, depth and composition etc.
Zeolite
Professor Richard Bell described the novel amendment Zeolite to the group; a type of rock with high surface areas that is known to be good for water retention, cations and holding potassium.
Compost + Clay
This amendment was made by adding Watheroo bentonite (high quality) clay at a ratio to C-Wise Humicarb. This combination is commercially available as a mix however there was discussion around the potential to source clay closer to the property and obtain the compost separately as a more economically viable option.
Ironman Gypsum
As with the Zeolite, Professor Bell describe the novel amendment Ironman Gypsum; a byproduct of synthetic rutile, sourced from a local mine site. Its make-up is mostly gypsum with some iron, aluminum and magnesium oxides and is know to be good at increasing PBI. This amendment has the potential through the iron aluminium to lock onto carbon, making it stable long term. Attendees discussed the likelihood of aluminium toxicity and decided as long as the pH is right, there shouldn’t be an issue.
Local Clay
The local clay was sourced on-farm and composed of 25% clay and was distributed at 100T or 25t/ha. Conversation around this amendment suggested to not go for anything less than 25% clay, as you will end up just adding a larger percentage of sand and increasing the cost. The group decided that you want 30%+, being careful to not go too high as it can pan up and doesn’t spread well.
Biochar + Frass
WMG CEO Nathan Craig gave a description of the biochar and frass amendments added in 2022 to the group. Biochar is charcoal like substance made by burning organic matter such as wood in a controlled environment, and is a soil amendment that works over the long term by increasing surface area and porosity of soil and adding carbon. Frass is made of soldier fly castings, a natural insect manure that is a byproduct from the animal feed industry.
For this trial, biochar was spread at 10t/ha, however there was some conversation on the rates that would be needed to provide a result with suggestions that at least 25t/ha was necessary. This conversation was followed by a discussion on the feasibility of spreading biochar at paddock scale, and options to reduce fine ‘soot’ while spreading – such as by wetting the biochar before use.
As part of the carbon conversation introduced by Professor Richard Bell, attendees also discussed 5 rules associated with soil carbon:
Soil Carbon Rules
- You can add carbon – but this does break down with ‘use’
- You can grow carbon by increasing organic matter
- You can add amendments that can ‘lock in’ carbon
- You can reduce disturbance to allow for build up
- The deeper the carbon can be placed/built, the more stable it will be
Economics
There was a general consensus on the need to look into the economics of the novel amendments that were used within this project. Examples of gypsum and biochar being expensive when you include factors such as freight and amount needed to be spread. There needs to be a demonstration of the returns with each of the novel amendments if they are to be useful to farmers.
Amelioration
The soil amendments discussion was followed by an investigation of the soil amelioration methods used at the site, including a small soil pit of each method.
Three types of amelioration were implemented in this trial (spading, mouldboard and shallow tillage). The spading was remarked to have been done ‘right’ at this site. Attendees saw evidence of operator speed accuracy and noted the machine did a good job of diluting the non-wetting soil with minimal pocketing.
The mouldboard indicated the greatest initial impact but needed a skimmer to not produce mounds on either side of the treatment, this visually skewed what everyone thought was the ‘best’ treatment amongst all plots.
Attendees discussed how to deal with paddocks like this that blow when wanting to ameliorate, with suggestion of winter amelioration followed by fast growing first crop as well as using rollers/smudgers etc.
There was a general consensus that we know the effects of the soil amelioration methods used at this site, less so about the interaction with amendments.
More Information
For more information on the Future Carbon Project, head to the project page. If you are interested in a full set of notes from the event, please contact Kate Parker at projects@wmgroup.org.au.
This project is supported by the Western Australian Carbon Farming and Land Restoration Program, The CRC for High Performance Soils (Soil CRC), and Future Green Solutions.
