SoilsCon returned this week after a four-year hiatus, much to the delight of its 150 delegates. Organised by soil scientist and landscape consultant Tim O’Hare, the one-day conference not only reaffirmed existing knowledge but also brought with it a whole host of new information on soil.

There’s too much to list in one article – you’ll just have to attend the next one – but here are a few of the key things we picked up from the eight insightful sessions:

1 ‘Soil health’ is (finally) the new buzzword

There’s more to this than first meets the eye, and a baseline soil survey can help determine the health of the soil.

2 Compaction is the biggest contributor to soil degradation in construction

A ‘traditional’ soil profile is often 150mm of topsoil above compacted subsoil, but this is a “dysfunctional landscape” says soil scientist Tim O’Hare. An ‘optimised’ soil profile is 300mm of topsoil above 300-600mm of decompacted subsoil.

3 Soil organic matter plays a fundamental role in soil functioning

It’s the portion of soil derived from organic matter that glues the soil aggregates – or the ‘crumbs’ – together. When it’s low, the structure collapses, carbon can be lost and there can be poor root growth. Increasing the soil organic matter increases the workability of the soil, explains Dr Iain Gould, associate professor in Soil Science at the University of Lincoln.

4 Oxidation and aeration is a key contributing factor to losing soil organic matter

And one of the most effective methods for building it is compost.

5 Biodiversity net gain guidance includes just a brief mention of soil

BNG is “a bit like an MOT test,” says Tim White, senior associate at Tim O’Hare Associates. It’s not a guide to habitat creation but instead will score you on it – on whether there’s low, medium or high value to wildlife of habitat. Soil gets a mention in the BNG Technical Annex 2, in sections 6.2.7 and 6.2.8 – two paragraphs in total, focusing on low soil nutrient status (which we suppose is better than nothing).

6 Low fertility soil helps to create habitats but along with other factors

The BNG guide is not wrong – low fertility soil is important, with the pH and phosphorous value being key. High fertility soils can favour aggressive species or need additional management. But there are other environmental factors that need to be taken into account, such as whether the site is prone to drought or is steeply sloping.

7 Soils should be properly managed and prepared to ensure high quality habitats

The habitat design should account for the soil type, and soil preparation should target the shortcomings for both on-site developments and off-site BNG projects, says White.

8 Soil is not just ‘dirt’

Garden designer Helen Elks-Smith says she is constantly having to teach housebuilders – and sometimes even landscape contractors – the important of soil to the success of a scheme, often being “gaslit” on site. Poor soil management can lead of the failure of the planting scheme, costing the client more in the long run. To avoid liability, Elks-Smith ensures she has “tight contracts” in place with “many caveats”.

9 The domestic market is “lagging behind” in this cultural shift

The commercial market is “so much further ahead” than the domestic sector in terms of understanding the role of soil, says Elks-Smith.

10 Consider ‘soil protection zones’

To protect the soil rather than having to salvage it, Elks-Smith encourages soil protection zones to avoid compaction, for instance.

11 Soil was a project in its own right for the Woolbeding Glasshouse and Silk Route Garden

Soil profiles were created for all 12 different zones and transitions of the new garden and the impressive 10-sided glasshouse designed by Heatherwick Studio. Jennifer Mui, director at MRG Studio, ran through the low-fertility soils considered for these climate-resilient landscapes. The National Trust will be monitoring the site to see what takes in what conditions and the biodiversity.

12 SuDS shouldn’t “take up space”

Instead, they should be woven into the fabric of every development, says Kevin Barton, director at Robert Bray Associates. Sustainable Drainage Schemes (SuDS) should also be a landscape-led discipline, he adds.

13 SuDS spaces should be functional, even when it’s not raining

Rather than solely serving the purpose of managing rainwater, these gardens should be inviting for when the British weather is surprisingly sunny.

14 SuDS are “one of the biggest asks of soil”

Soil is expected to do a lot for SuDS schemes, from filtering silt and the bioremediation of pollutants, to encouraging healthy plant growth, says Barton. Runoff – or rainwater – carries with it various ‘inputs’ that the soil has to deal with.

14 “Build less and build properly”

If a local authority can’t afford to properly maintain a raingarden, then it should build fewer of them and maintain the ones that it does have, says Barton.

15 Biochar and dolerite could accelerate habitat creation when incorporated into soil

Biochar – a carbon-rich form of charcoal produced by pyrolysis of organic feedstock – and dolerite, which is a type of igneous rock, can help to establish habitats. Arup’s senior geotechnical engineer Katherine Iles and senior landscape architect Ryan Coghlan are trialling its use as part of the HS2 project to quantify its benefit in the landscape.

16 There are regulatory barriers around biochar

“The regulator does not know what to do with this material,” says Iles, who says it is in the waste hierarchy but is not defined. Through their BEIS Phase 1 Study – to discover the carbon removal potential of biochar or dolerite and to demonstrate its potential for large-scale applications – and the HS2 pilot study, Iles and Coghlan are hoping to build an evidence base to close the policy gap.

17 Ensure biochar is sustainably sourced when purchasing

Rather than forests being acquired and trees being chopped down for the purpose of producing biochar, it should be produced from waste materials to avoid having a negative environmental impact.

18 BNG doesn’t take soil biodiversity into account

There’s no regulation around soil biodiversity like there is around biodiversity above ground (for example, BNG), says Helen Simmen, who leads the research and development department at Wildflower Turf Ltd. And yet “soil hosts more than half of life on earth,” making it the most biodiverse habitat on the planet.

19 Soil is an “opportunity, not a problem”

It’s the cornerstone of an ecosystem, says Simmen.