Soil is central to all aspects of our lives, from producing food (of which 95% comes from production systems reliant on soil) to regulating water supplies, and potentially maintaining environmental quality.
It was Franklin D Roosevelt, former President of the United States, who famously said in 1937: ‘A nation that destroys its soil, destroys itself’. If this is the case, then we are rapidly destroying ourselves. Earlier this year, the UN Food and Agriculture Organisation (FAO) reported that an area the size of one football pitch of earth erodes every five seconds globally, which means that 90% of the Earth’s topsoil is potentially at risk by 2050.
When we consider that less than 7% of the Earth’s surface is suitable for agriculture, and that it takes thousands of years to effectively produce new soil, then the reliance we have on our earth to sustain ourselves is fragile, and frankly, unsustainable.
As the James Hutton Institute, an independent research organisation delivering fundamental and applied science to drive the sustainable use of land and natural resources, we have almost 100 years of experience in soil research and plant breeding from our current and predecessor bodies. We have over 400 scientists, amongst them a number whose focus is on below ground processes, from fundamental plant-soil interactions, to understanding soil management impacts at a catchment/landscape scale.
Soil biodiversity has been referred to as the ‘factory of life’. Soil biological communities can be simplified according to their role in the soil web as being ecosystem engineers (for example earthworms), litter transformers (such as arthropods), and the micro food web which includes bacteria and fungi (including nematodes). When we consider that one square metre of forest soil can hold over 1000 species of invertebrates, with a single gram of this holding millions of bacteria and soil generally holding 25% of the planet’s biodiversity; it is indeed a large factory.
“one football pitch of earth erodes every five seconds globally”
Given the climate crises we are currently facing, recognising the potential of soil in mitigating the challenge through changes in its management is integral to solving this global problem. However, it is a delicate balance to strike between maintaining the provisioning services of soil (such as the production of food) whilst minimising drivers of climate change (greenhouse gases) and also managing the landscape to be resilient to changes in weather extremes. For example, if we remove trees to make more land available to grow crops, we reduce land cover provided by the trees, which can expose the soil to erosion from wind and water, and increase flooding.
This erosion can create a negative cycle: it reduces carbon stores in the soil allowing previously stable, locked up carbon to be open to the elements and released as carbon dioxide through mineralisation. This then changes the climate further, affecting rainfall intensity, which increases erosion, escalating carbon losses, which can affect rainfall and so on. This is an extreme example and one that many are acutely aware of when considering land use and the need to minimise soil losses.
Another example relates to the drive to plant trees and increase soil carbon. Trees have significant potential to store carbon both in their vegetation and in the soil due to below ground root activity. Decreases in soil carbon have been observed with changes from grassland to cropland, however, at the Institute, our research has shown that changing from arable production to woodland production results in increases in soil carbon. Fundamentally, transferring soil use to an intensive production system results in a decline of soil carbon - whilst changing to a less intensive system has the opposite effect, and increases soil carbon.
“when it comes to soil there really is no “silver bullet” solution”
The Institute’s Dr Ruth Mitchell and colleagues have shown that tree planting on heather moorland, on organic rich soils, results in a loss of soil carbon in the initial decades. Their research found that there was a 58% reduction in soil organic carbon over a 12-year period following the planting of birch trees. Significantly, over a 39-year period since planting there was no increase overall in total carbon stocks (soil plus above ground carbon). The increase in above ground carbon due to the trees did not off-set the carbon losses from the soil.
It has been recognised for some time that the soil disturbance often associated with tree planting (mounding or ploughing) can cause major losses of soil carbon. This study had minimal soil disturbance (the trees were slot planted) and it is thought that the soil carbon losses were due to soil priming. The addition of carbon to the soil from root leachates and leaf litter resulted in increased soil microbial functioning.
Soil microbes consume carbon; with increasing microbial activity in turn releasing carbon dioxide from soils, this carbon dioxide is often used as a proxy measure for soil microbial activity.
This is one study shows the potential complexity of how we manage our landscape and underlines the importance of understanding that one approach does not fit all in many situations. The findings of these studies were related to managing planting on organic rich soils, however, when you consider that Scotland has over 40 sub-groups and 800 individual types of soil, we must ensure that recommendations are appropriate within prescribed limits. Importantly, it also demonstrates that when it comes to complex systems like soil and complex problems like climate change, there really is no “silver bullet” solution to the problem.
Searching for solutions
Work at the James Hutton Institute is wide ranging, encompassing many aspects of critical importance in mitigating the impacts of a changing climate. Increasing the resilience of systems is of primary importance, not just for maintaining food security, but also in ensuring soil functions are maximised through the adoption of robust management strategies.
Two examples of this include work on the potential benefits of diverse cropping systems and intercropping to maximise yield and reduce inputs, and work looking at nature-based solutions to mitigate against flooding. Just two projects of many that are looking to increase biodiversity in the wider landscape for multiple benefits.
This is particularly relevant given that this year, COP15, the UN Biodiversity Conference, will look at agreeing the goals for a framework with the aim of ‘transformation in society’s relationship with biodiversity’ and that ‘the shared vision of living in harmony with nature is fulfilled’.
Our research develops better understanding of biodiversity and ecosystem function by creating general principles that advance scientific thinking and its application into farming practice. Understanding the potential benefits of biodiversity in food production systems allows biodiversity – above and belowground – to be valued by policy makers and society. To do this, we work with farmers, agronomists, processors, and regulators to inform on new approaches alongside trialling new practices on commercial farms. These approaches ensure a robust scientific basis on which decisions can be made.
Intercropping, where two or more plant species are grown together, has the potential for significant benefits through harnessing the diverse plant functions associated with different plant characteristics (or traits). These can include using nitrogen fixing legumes to produce ‘free’ fertiliser from nitrogen gas in the air; creating structural diversity in the canopy to increase light capture and suppress weeds, and in the roots to increase soil exploration for nutrients and water, and buffer soil erosion; as well as providing a greater variety of plant resources above and belowground for beneficial organisms such as pollinators, decomposers, and the natural enemies of pests. Understanding which plant types work best alongside others is key in making the most of this approach to managing soil and land for wins such as increasing yield, reducing fertiliser and herbicide use, enhancing biodiversity, and preserving soil.
“changing climate has shown the potential implications of drought on our food security”
Plant teams within an intercropping system could deliver multiple benefits, dependent on the greatest need. Nitrogen fixation is one example, however there are also opportunities in relation to phosphorus (P) with P-mobilising species being used alongside plant species without this trait. Aside from nutrients gained from the soil, plants also require water to thrive, yet a changing climate has shown the potential implications of drought on our food security, further increasing pressure on our agricultural systems.
Similar to the role of different plants species in fixing and mobilising nutrients, plants can also create hydraulic lift, a function where water deep in the soil can be transferred closer to the surface through its root systems.
Through this vertical movement of water, plants with shallower root systems to still have access to water where they may otherwise not. This function effectively improves the growth of shallow rooted species during periods of drought. The increasing frequency of extreme weather including heat, drought, and heavy rainfall has highlighted the potential implications of the changing climate on our food security and supply chains. Increased plant diversity offers one method for mitigating these pressures on our agricultural systems while simultaneously addressing the biodiversity crisis.
“increased plant diversity offers one method for mitigating pressures on our agricultural systems”
More recently, European research funding was awarded for the Root2Res project, led by the James Hutton Institute. Root2Res will explore the genetic markers within plants linked to increased resilience against stress caused by climate change. Understanding the genetic markers and how they are linked to specific belowground traits (such as the ability to access more nutrients through root hairs) will be measured alongside plasticity and the ability of a variety of cereal, tuber, and legume crops to heritably cope with environmental stress and deliver a stable yield. Plasticity relates to the ability of a plant to respond and adapt to changes in its environment. Heritability is an understanding of how much of what is observed for a plant can be attributed to genetic variation rather than as a result of the environment that it grows in. The need for such work is critical, as evidenced by the droughts across Europe in 2022. European crop yield is expected to decrease by 30% by 2050, necessitating the breeding of crops with increased resilience, and the ability to cope with a changing climate.
We are seeing soil quality and health moving further up the political agenda due to the multiple benefits a healthy soil can bring. In order to reward those managing their soils sustainably, however, we require an effective and robust soil monitoring framework which uses indicators relevant to the targets looking to be achieved. Such targets may differ based on expectations for the land, and more fundamentally what we are using the land for.
“soils are vitally important to our survival, and as a society we should change the way we think of them”
Complexity comes from understanding which indicators work best for a specific land use type, something that Hutton is actively working towards validating through funding from Scottish Government’s strategic research programme.
Within the European Union, understanding soil health indicators is key, with an ambitious plan to achieve healthy soils by 2050.
There is no panacea regarding soil health indicators, no single measure can tell you if a soil is healthy. Soil carbon, for example, is important but just because a soil contains high or low levels does not mean it is necessarily ‘unhealthy’. A sandy soil, for example, is likely to have a lower soil carbon content than a clay soil, but this is due to fundamental soil properties rather than it being poorly managed. Carbon is one measure which can be used to assess soil’s physical and biological health, but what about its chemical health, the third core component? Understanding of indicators and thresholds for different soils is vital to assess its health, as well as a focus on the desired function of the soil – be that food production or reducing flooding.
Soils are vitally important to our survival, and as a society we should change the way we think of them. They must be respected and nurtured for all the important functions they serve, otherwise we may, as Roosevelt said, end up destroying ourselves.