Soil health – how quickly can you reset a soil?

Project Fortress is hosted at The Grange Farm in Northamptonshire and is a collaboration on soil health between host farmers, Andrew and William Pitts, and BASF. They have divided a 12.5ha field sitting on Hanslope clay into five plots where different approaches, each designed to improve the land’s climate change resilience and profitability, are being implemented and analysed.

“We’re testing techniques that will enable these soils to better cope with the weather extremes that climate change is, and will, throw at it,” explains Mike Green, BASF agricultural sustainability manager and project lead.

Enhancing soil health and biodiversity

Extended spells of dry weather, combined with very short periods of heavy rainfall tests soils’ capacity to simultaneously absorb and retain water. The five plots are all designed to improve infiltration and increase organic matter. As a commercial farm, the need to produce profitable crops hasn’t been ignored. Neither has biodiversity, which is recognised for its agro-ecosystem services of pest management and pollination.

“Fundamentally, it’s about balance and resilience,” surmises Mr Green.

Alongside the broadacre crops, the plots include three- and four-year herbal leys with grazing sheep and ‘supercharger’ cover crops. The plots are interspersed with what the team are calling ‘agrofloristry’ – 2m of undisturbed grass between two 3m meadow flower strips – as well as being topped and tailed by headlands which have been taken out of production to be ‘reset’ under a three-year meadow mix.

Degraded topsoil

Professor Jenni Dungait has been analysing the the soil health since the baseline year in 2021:

“When I first looked at this field, it was clear that it was degraded.

“At the top of a hill, it’s what would traditionally be called a ‘scald’, and over generations, much of the best soil has been carried to the bottom of the hill by wind and rain. With little topsoil above the bedrock, it is stony and vulnerable to compaction.”

Ahead of the first year of Project Fortress, Prof Dungait took soil samples from across the field and the adjacent woodland. She expected to find the cultivated areas contain very little carbon and have poor structure.

“Surprisingly, at about 6.5%, the topsoil across this field had very high levels of organic matter for their type, topography and climatic conditions, making it difficult to improve.”

Despite the challenge, the herbal ley with rotational grazing by sheep has increased the organic matter content of the topsoil by 0.5% in just two years. “In this context, and understanding how long it takes to build organic matter in soils, that’s a huge increase,” notes Prof Dungait.

Compacted subsoil

Below the traditional plough depth of 8in, it was a different story: “The sub soil is compacted and has a comparatively low organic matter content of 3–4%. So that’s where our focus has been – getting carbon-containing organic matter down deep into the soil profile.”

Contrary to current trends, Prof Dungait suggested subsoiling to alleviate some of the compaction, enabling water penetration and the plants in the trial plots a chance to get their roots down.

“We needed to make a drastic impact on how this soil is performing. We’re already seeing the effects of climate change here, with the land experiencing high rainfall and drought, so the pressure is on to get this soil performing quickly,” she explains.

Prof Dungait and the team assumed that none of the deep-rooting plants in the herbal and cover crop mixes would be able to get through the remaining patches of compaction. “We were wrong. Given a second season, the chicory grew to over 5ft tall and its roots just about broke through. However, the thin spidery threads would take years to achieve what a sub-soiler can do in a pass.

“The taproot of the sweet clover also penetrated the tightly packed layer. It’s really important. We’re achieving one of Project Fortress’ primary objectives and getting carbon deep into the soil, both through the root mass and the carbon-rich exudates it’ll be releasing into the soil. That root will be keeping the soil structure open, allowing air and water to penetrate. It’s an incredible achievement in just two years.”

Excitement for the future

With a further three years of trials and analysis in Project Fortress, the team is really excited about the future. “The pressure is on,” says Mr Green. “Climate change is fast accelerating, and we need to adapt.

“Project Fortress is the ideal space to look at both the impact of climate change, and some approaches to building resilience on farm. It also gives us a platform to share knowledge and engage with those at the forefront of decisions that will impact the industry for generations, and our thanks go to the Pitts family for supporting the partnership.”