Access to water and nitrogen (N) in the soil is influenced by root-soil interactions within the “root zone” or rhizosphere. The rhizosphere is a dynamic, heterogeneous system that actively changes the characteristics of the soil.
For regional agricultural applications, reliable soil moisture products are needed at high spatial and temporal resolution in the root zone. This is especially important for estimating the rate of deep water uptake by roots.
The Impact of Living Soil Systems
The root zone is where most of the water, nutrients and carbon cycling in soil occurs. It is also the interface between the living and non-living components of Earth, and is teaming with billions of bacteria, fungi and other microorganisms that form the foundation of an elegant symbiotic ecosystem. It is the engine of life, a key to our planet’s health and vitality.
But, even though the root zone is a central part of the landscape and critical to all terrestrial processes, we still don’t fully understand it. It is a term that has been used in hydrology, agronomy and land surface process studies, yet it lacks a precise definition, and the role it plays in our Earth systems is often under-appreciated.
This is despite the fact that it is responsible for a huge proportion of our food production. The structure of the root zone determines how much water soil can take up and retain, how it is filtered and enriched, where it goes with rain or irrigation, how it is used by plants, and so on.
In a living soil system, roots can grow deep into the soil to recover resources such as nitrate or phosphorus that have been accumulated there since the previous crop. The microbial activities described above support this process by converting the organic matter in the soil to more usable forms.
However, this is not always possible when the structure of the soil has been altered by tillage or chemical fertilizers. In these conditions, the network of living roots and fungi is damaged, leading to more compacted soils with less infiltration and more runoff and nutrient loss. This is why we need to develop living soil practices that restore the health of our soils and can support a diverse range of species.
Living soils are full of biodiversity and provide a range of benefits for humans, animals and the environment. They can increase soil fertility and moisture retention, help reduce the need for pesticides and synthetic fertilizers, and improve the performance of agricultural crops. In addition, they are often better able to cope with climate extremes than conventional farming practices.
The Benefits of Living Soil Systems
Living soils are teeming with beneficial microbes and organisms, and they support a healthy ecosystem, especially at the optimal gallons for living soil. They are also rich in organic matter, which allows water to move easily through the root zone, delivering hydration and nutrients to plants. Organic matter also promotes good tilth and increases aeration.
The living nature of the soil also makes it resilient to stress and drought. In general, healthier soils hold onto more moisture and are less prone to erosion, which reduces the need for irrigation and fertilization. Living soils are a key component of sustainable agriculture, a growing movement that uses holistic management practices to produce high-quality food while reducing the environmental footprint of farming.
One example of a living soil practice is cover cropping, a method that involves planting a temporary vegetation over the fields before harvest. This provides a natural source of mulch and protects the soil from sun, wind, and hail damage. Other living soil practices include adding compost, manure, and other organic material to the field, which encourages the growth of microorganisms that help to break down organic matter into plant nutrients.
A national living soil repository would preserve a representative sample of the nation’s terrestrial biodiversity as a valuable natural resource, and serve as a baseline for tracking changes in genetic diversity over time. However, the cost of establishing such a repository has been a major challenge to date.
Living soils can also increase crop yields and reduce the need for chemical pesticides, which are costly to produce and have harmful side effects on human health and the environment. These benefits are due to the fact that living soils are more nutrient-rich and more resilient, and they allow plants to access these nutrients more effectively.
In addition, living soils can be used to monitor climate change and other anthropogenic impacts on ecosystems. The structure and health of a given soil determines the quantity and quality of its ecosystem services. For example, a healthy soil will have a large diversity of microorganisms, which decompose organic matter and recycle it to the roots, improving soil texture and water infiltration. A healthy soil will also be less acidic, which is important for the health of crops and soil.
The Challenges of Living Soil Systems
Soil ecosystems are highly complex, supporting a multitude of organisms in an incredibly diverse habitat. These organisms are a vital component of the global carbon, water and energy cycles. They are also responsible for numerous other functions, including:
Soils provide a medium in which plants can grow (pictured here during a cover crop workshop), water supply and filtration, recycling and storage of organic matter, shelter and food for a wide variety of animals, and more. However, they can also be difficult to understand.
While most scientists agree that soil is a dynamic and important part of terrestrial systems, there are still many challenges to understanding how it works. Among these is the difficulty of directly measuring soil moisture at large scales, which limits our ability to explore how the root zone responds to climate change and other anthropogenic drivers.
Although meteorological drought is a key factor in runoff generation, plant growth and land-atmosphere interactions 1,2,3, it has not yet led to any overall global decline of vegetation productivity. This suggests that belowground ecosystems have developed strategies to adapt to meteorological and human-induced droughts, which are likely mediated by changes in the spatial and temporal dynamics of root zone water storage capacity (SR).
SR is the amount of available water stored in soil at depths accessible to roots, and can be influenced by a number of factors, including landscape and climatic features, irrigation practices, and management decisions 4. It may also be affected by local anthropogenic activities such as deforestation and groundwater extraction, and global changes such as increased air temperature and precipitation variability 5.
It is possible to measure SR using satellite remote sensing data of bare soil surface evaporation, but it can be challenging to scale up to a global level due to the inherent complexity of calculating the spectral shape of SR (Eth) at varying water deficits 6. The lack of a globally quantitative, dynamic model of SR has made it difficult to develop effective mitigation strategies 7.
One promising approach is the partial root zone drying technique pioneered by Brian Loveys and colleagues in southern Australian vineyards 8. In this experiment, alternate halves of the vine’s root system are irrigated to sustain dry root zones without compromising the plant’s water status. This has the potential to significantly reduce transpirational water loss and improve plant vigor, while simultaneously reducing excessive irrigation use 9.
The Future of Living Soil Systems
Despite being one of the most complex ecosystems on Earth, we still have much to learn about soil and the living biodiversity that makes it tick. But a growing movement is underway to build an understanding of what’s happening underneath our feet and how that can be used to support thriving, resilient agricultural production.
This approach is based on the concept that reversing the decline in soil health by enhancing organic matter and improving biological diversity will lead to improved crop yields and environmental outcomes. It focuses on using natural inputs like perennial legumes and cover crops to improve macro-porosity, enhance the availability of nutrients (including nitrogen) and provide an environment that is more welcoming to root systems. It also uses genetic tools to develop improved rooting systems for more efficient use of resources.
Many of the key ingredients for this are already available, and we know that a wide range of management strategies can be employed to maximize their potential. These include improving crop rotations, varying fertilizer rates and adjusting the timing of applications, as well as integrating the addition of organic matter, like compost. The results so far show that these approaches can provide significant improvements in both crop productivity and environmental outcomes.
A key factor in improving root system performance is increasing the depth of the root zone, which allows for greater access to limiting soil water and nutrients. The ability of roots to do this is influenced by both the soil itself and the type of crop. For example, a study of the benefits of deep rooting in wheat found that while the value of deeper roots was consistent across seasons, it was significantly influenced by crop management. For this reason, it is important to understand the farming system context in any studies of proposed genetic improvements to root traits that are designed to improve productivities or environmental outcomes.
The living soil movement is about more than just increasing food security; it’s about restoring the vitality of our most valuable natural resource. This film, produced by Tiny Attic Productions, showcases the efforts of farmers, scientists and others to help sustain this critical, teeming network of life.
