Soil: The Solution for Food Security and Climate?
Under climate-smart management, can agricultural soils lessen the impact of climate change and offer food security to a growing population?
Without soil, life as we know it would simply not exist. Healthy agricultural soils produce nutritious food and support wider ecosystem services. Sadly, inappropriate management has degraded agricultural soils globally, exacerbating food insecurities and accelerating the impact of climate change. Climate-smart farming, or regenerative agriculture, aims to correct those effects by utilising low-impact, sustainable practices to restore and improve soil quality. Evidence suggests widespread implementation of these practices would secure long-term global food production and offset global carbon emissions.
The need for change.
Picture this: a trail of gulls dip and dive behind as a tractor ploughs its way across an open field. Gulls swoop down, picking off insects from the freshly ploughed soil. This image illustrates ploughing in action, a farming practice common across the globe. The long-term effects of industrialised farming have come under heavy criticism, in particular the plough. Ploughing is a deep inversion of the soil that redistributes nutrients throughout the soil profile. This can facilitate a crop’s access to vital nutrients, thus increase yield. However, these benefits are lost as soil quality deteriorates with regular deep inversion.
Ploughing, or tillage, weakens the soil structure. A weakened soil structure allows nutrients to be lost via leaching. In order to compensate for nutrient losses and achieve maximum yields regardless, farmers apply a range of chemical fertilisers. Fertiliser runoff then leads to a chemical build up that pollutes waterways causing widespread environmental harm. Additionally, microbial decomposition of these fertilisers emits nitrous oxide, a potent greenhouse gas 300 times more harmful than carbon dioxide. This cycle of fertiliser input and subsequent fertiliser losses ignores the root of the problem: poor soil quality.
Years of using heavy machinery and agrochemical inputs to manipulate the land have sterilised agricultural soils, resulting in loose, poor quality soils highly susceptible to erosion by wind or water and unable to support crop growth. The Southern Plains of the U.S. suffered the impacts of degraded, fallow soils in the 1930s Dust Bowl. High winds whipped eroded soils into dense clouds during a drought period. Soil management practices were quickly revised in the U.S. following this, however change has not been so readily accepted by other nations.
90 years later and agricultural land the size of Portugal is still lost annually due to soil erosion. Over 40% of Earth’s soils are currently under threat from soil degradation, a process climate change is expected to worsen. Conventional methods such as ploughing are exacerbating this issue. It is clear the need for an alternative agricultural system is great.
Agricultural reform.
Regenerative agriculture seeks to imitate nature by limiting soil disturbances and maintaining constant plant coverage. Climate-smart farmers plant crops on set rotations, specific to soil type and climate. Ideally they also allow for periods of livestock grazing. Cover crops such as vetch and beans are planted after harvesting the cash crop to avoid bare soils, a significant contributor to soil carbon losses. Legumes such as beans fix nitrogen into the soil, reducing the need for chemical fertiliser additions. This makes them a particularly valuable component in soil regeneration systems.
Reducing tillage intensity is often step one when converting to climate-smart farming. Extensive research has shown both minimum till (turning just the top ~15cm of soil) and no-till improve soil quality. Under no-till management, a direct drill replaces the plough. It works as the name suggests: drilling seeds directly into the soil, minimising topsoil disturbance, so allowing the soil to maintain its structure. Combined with cover cropping and carefully defined, diverse crop rotations, a no-till system mimics the natural rhythm of the land.
One farmer firmly in favour of supporting this fragile system is Carlos Crovetto. Switching to a no-till system 46 years ago provided a lifeline for his farm in the severely eroded foothills of the Andes, south-central Chile. Crovetto’s strong desire to protect his land for the future, damaged by years under the plough, motivated the switch. Today the farm is a shining example of the benefits of regenerative agriculture. Through years of experimentation Crovetto has crafted a system of no-till with cover crops replacing degraded lands with productive, fertile soils.
Carbon-smart?
Restoring soil quality increases agricultural resilience. This resilience is becoming increasingly vital as climate extremes amplify both environmental and societal uncertainty. Regenerative agriculture may go beyond just adapting soils to face climate change. The Rodale Institute, alongside other research bodies, have proposed these practices as a pathway to reducing atmospheric carbon, making a switch to these farming systems climate-smart and carbon-smart.
Soil management determines whether the soil will act as a carbon sink or source (other factors such as biomass content and climatic conditions are also influential). Undisturbed soils with constant plant cover drawdown carbon dioxide from the atmosphere. A new study suggests 23.8 gigatonnes of carbon dioxide equivalent could be absorbed by global croplands each year – soil carbon alone holds a quarter of the total emissions reductions offered by natural climate solutions. This study, published in Nature earlier this year, indicates 60% of this carbon storage potential comes from the rebuilding of degraded soil carbon levels. Agricultural methods which work to regenerate depleted soils, such as no-till and cover cropping, are key to unlocking the storage potential of farmland.
However, carbon sequestered through agricultural management choices is not locked in indefinitely. This reversibility of soil carbon storage has been well explored in scientific literature. When first implemented regenerative management initiates a faster carbon storage rate. This rate declines over time, therefore agricultural soil cannot be expected to remove 23.8 gigatonnes of carbon dioxide equivalent each year for the rest of time. Precisely how this decline plays out is dependent on soil type, management and climate, but research suggests it begins after some decades. Therefore, soil’s carbon storage potential, no matter how great, cannot be seen as a safety net.
A warmer world looks likely to put the carbon-smart nature of regenerative farming into jeopardy. Research from a study of Panama’s lowland tropical forest soils found approximately 13% of the total soil carbon stock was lost when soils were kept at 4°C (39.2°F). 13% equates to between 5 and 7 tonnes of additional carbon losses; a figure roughly equivalent to the average annual carbon dioxide emissions of a family car.
Equally, structural disturbances from a return to higher intensity tillage would almost immediately release the hard-earned carbon back into the atmosphere.
Key players in regenerative agriculture argue the uncertainty surrounding soil as a mitigative measure for climate change is undermining efforts to convert farming systems. An assessment of current soil carbon science argues scientific consensus does exist: soil carbon must be rebuilt for sustainable land stewardship. Regenerative farming is an effective method for doing so.
Offsetting potential aside, management which restores soil quality supports a healthier future for both agriculture and the environment. Higher levels of soil carbon lead to an increase in soil organic matter. Organic matter supports healthy nutrient cycling and increases soil microorganism activity, so improving soil structure.
More carbon, more crops, less fuel.
If you still aren’t convinced of the merits of climate-smart farming, soils high in carbon are more resistant to erosion and disease so are able to support higher crop yields. Disease resistant, structurally stable soils supplemented with a diverse variety of crops have little need for additional agrochemicals. This eliminates fertiliser build up and associated environmental harms, enabling the wider ecosystem to flourish.
No-till pioneer Carlos Crovetto noticed that with healthy carbon-rich soils he relies far less on additional fertiliser inputs. Not fertilising or tilling has significantly reduced traffic moving across his fields. Putting scientific debates aside, no-till management requires less time on the tractor, making significant carbon savings by cutting farm vehicle emissions.
Feeding the globe.
Global agriculture today has the capacity to feed ~10 billion people. United Nations (UN) predictions state the world’s population will reach 9.8 billion by 2050. Looking at these figures you would be forgiven for questioning why food insecurity exists at all. We have the capacity to feed 128.2% of today’s population. Yet 8.9% of the world live with constant hunger. Eliminating food insecurity by 2030 is one of the UN Sustainable Development Goals.
Food security is a deeply complex issue, controlled by economic, geographic, societal and political barriers. Soil degradation exacerbates these factors, threatening the global accessibility of food resources. As outlined above poor quality soils cannot support healthy plant functions. Therefore, mismanaged soils produce low crop yields. Climate extremes are set to aggravate degraded soils, worsening food production in areas already suffering.
Rattan Lal, leading specialist in soil science and professor at the Ohio State University, places regenerative agriculture as a solution to global food poverty.
Food waste by the food secure contributes to the hunger of the food insecure. 30% of food produced is wasted, enough to feed a colossal 3.48 billion hungry people. Breaking the destructive cycle of production, waste, degradation and pollution requires agriculture to be reframed. From farmers to consumers the attitude towards food must change. As a long-term no-till farmer in the Aveyron region of France remarked, “the main tool is not the tractor, [the] main tool is the soil.”
Food production must focus on soil quality to produce crop quantity. Whilst we have the numerical capacity to feed an expanding population our attitude towards food production must change. Starting with the soil. Lal’s call for a “soil-based” shift towards gentler management methods such as no-till and cover cropping to restore our soils and sustain our population should be heeded.
Looking forwards.
Currently 12.5% of global arable land has been converted to no-till. Countries such as the U.K. and U.S. are pushing to implement legislation that offers financial incentives for farmers to adopt climate-smart systems. The Agriculture Resilience Act, passed earlier this year is the first comprehensive piece of legislation in the U.S. House of Representatives to address climate change and agriculture together. Brexit offers the U.K. the potential to reset the farming norm. Shifts are certainly underway.
Is soil the solution?
Uncertainty amongst the scientific community points to a need for further digging to uncover soil’s true position within climate change mitigation. Despite this, considerate agricultural management will be vital as climate change targets where society and farmlands are most vulnerable.
Picture this: acres of rolling fields of continuous, varied crops. Yellow ears of barley bursting with grain are disturbed only by herds of quietly grazing cattle. Is this the image future generations will associate with farming? Our total reliance on soil for food and climate security must hope that it is.
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