A first experience of subsoil amelioration on Chris Smith’s farm in western Victoria

When you cannot buy or lease land to expand, build your subsoils instead

Between Mount Arapiles and the Little Desert National Park is a gently undulating landscape with shallow lakes and crescent-shaped dunes, commonly referred to as Grass Flat.

Chris Smith and his wife Annette have been producing crops and livestock (sheep) from their 1000-hectare property at Grass Flat in the southern Wimmera for over 18 years. While Chris and Annette initially aimed to expand their property, low land availability and high land values kept this goal on hold.

Moreover, Chris’ frustration with large variations in yield – both within and between paddocks - changed their goal from expanding the farm to ‘doing better with what we’ve got’.

Difficult soils

In the past, the district was a seabed from time to time.  Over a geological timespan, the local area received large amounts of wind-blown deposits of soil. These formed the mixed soils that are currently home to the strong sheep and winter cropping farming system.

The surface soils range from coarse sands to medium clays across short distances. The depth and types of subsoils also vary in clay types and chemistries.

According to Chris, if the season is wet, the soil will be waterlogged; if the season is dry, the soil is bone dry.

Deep ripping not enough

Deep ripping was used for several years to improve drainage, aeration and root establishment. This, however, gave poor results with almost no noticeable change in the ripped clay - along with high fuel bills.

Chris felt strongly that something needed to be put into the rip lines to enhance the subsoil.

Chris tried increasing fertiliser and gypsum with test strips of heavier and lighter regimes, as well as tightening up his pest and weed agronomy. ‘I just wasn’t getting the yields or the consistency across the paddocks that should have been there,’ he said.

‘In the middle of summer, the top handful of sand is oven hot. Everyone keeps telling us how important soil organic carbon is but keeping it in a sandy topsoil is hard…it bakes away.’

Trying subsoil amelioration

Subsoil amelioration is the injection of organic matter underneath topsoil with the aim of placing it on top of a subsoil constraint to improve crop production. Subsoil constraints include issues like very tight clays or excess sodium, boron, aluminium, salt and high levels of acidity or alkalinity below the topsoil - which restrict plant growth.

In Chris’ case, he was mainly concerned about waterlogging and compaction of the subsoil. Soil tests on his farm also revealed high levels of magnesium and some areas with excess sodium or boron.

‘Early on, I thought about broadcasting different manures and organic materials, but I didn’t think they would stay,’ he said.

‘At the same time, I learned that local Agriculture Victoria soil scientists were researching subsoil amelioration. When I looked into it, it made a lot of sense to me.’

‘I thought the surface sand might be “gutless” but if the crop roots did a better job of getting into the subsoil clay, they would have much better access to water and nutrients.

I kept investigating and later got involved in a subsoil amelioration demonstration,’ said Chris.

Chris mainly focused on the sand hills. The sand sitting above clay does not hold nutrients or moisture well. The clay soils beneath the sand also have constraints; they rapidly become more alkaline with depth, waterlogged and compacted.

Chris said that while a very dry finish to the 2023 season was not ideal, the subsoil ameliorant should have had adequate soil moisture from the winter period to allow it to start working. Subsoil amelioration works best when there is adequate soil moisture in the following year.

Subsoil amelioration demonstration

In an Agriculture Victoria-led project, Birchip Cropping Group (BCG) set up a demonstration site on Chris and Annette’s property to help Chris and other growers in the district see first-hand the impacts of different methods of subsoil amelioration.

Chris lined up sources of composting materials and had started some of his own compost heaps.

The demonstration included a range of treatments including gypsum, pig compost, deep ripping and a treatment called “Chris’ home brew”, consisting of duck manure and straw. The amendments were applied at different rates and depths.

The demonstration strips were 8 metres wide. ‘The yield monitoring in the header was a little bit washed out because of the overlapping strips but during the growing season you could see the effect on the crop; there were more leaves on the plants growing in the compost strips,’ he said.

Challenges to overcome

The home-made compost was much lighter and fluffier than the pig compost. Chris said in future, he will have to consider how to apply heavy rates of his own compost into the soil. Other considerations included the risk of the material clogging the chutes (also called “bridging”) and how tweaking the recipe of the compost might produce a different material.

The high hopper on the contractor’s subsoiling machine required a telehandler to load. The support frame also made access difficult, should the tyres need changing in the field, Chris said.

The machine had started life with closed funnels to a solid boot behind the tyne but had been modified because of bridging. Observing all these issues and the way the machine worked helped Chris decide to build his own machine.

‘My own subsoiling machine is being built and I am building up a stockpile of compost. I know there may be some value in targeting only areas in the paddock where the subsoils will respond better to the organic matter - but for the moment I am going to do my sandy rise paddocks.

I will also do some test strips in other paddocks and watch how they perform.’

Considering subsoil amelioration?

For farmers considering subsoil amelioration, determine whether there is a subsoil issue first by doing soil tests and looking at several years of yield maps and Normalised Difference Vegetation Index (NDVI) maps. If an area is consistently falling behind the water limited yields by a fair margin, subsoil amelioration might be worthwhile. Only a few subsoiling contractors exist in Victoria, so securing one and having a large supply of organic matter are the main challenges.

Agriculture Victoria has produced a factsheet on subsoil amelioration for grain growers in the medium and high rainfall zones of Victoria.  https://agriculture.vic.gov.au/crops-and-horticulture/grains-pulses-and-cereals/decision-support-for-grain-growers

Acknowledgements

Prepared by Adam Buzza, Agriculture Victoria, with thanks to cooperator Chris Smith and demonstration by Birchip Cropping Group.

The demonstration was part of a larger project, funded by National Landcare Program Smart Farms Small Grants – an Australian Government initiative and the Grains Research and Development Corporation.

Further information

Fact sheet: Decision support for grain growers

Podcast: Planning for the dry by improving our subsoils with Chris Smith

Video: Subsoil amelioration