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Soil is the upper layer of the earth’s crust. It consists of a mixture of mineral particles, organic material, organisms and liquids, and has various physical, chemical, biological and morphological properties. It sustains plant life, which in turn sustains the lives of animals and humans.

Since we rely on soil to supply food, feed and fibre to the world, it is an essential natural resource. Furthermore, it is not merely a substrate for the growth and proliferation of plants, but it also maintains environmental quality through services like the decontamination of water, sustaining biodiversity, maintaining ecosystems, and serving as a carbon sink.

Despite its significance to the survival of life, soil is constantly degraded mainly through agricultural processes. More than 50% of agricultural soils are moderately to highly degraded. Soil degradation is the result of erosion, pollution, extensive cultivation, overgrazing, and land clearing. Moreover, the growing human population increases the demand for feed, fibre and food, and puts immense pressure on all natural resources, including soil.

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What are soil health and quality?

Soil health is associated with the fitness of the soil to function as a system to sustain biological productivity, environmental quality, and animal and plant health. The concept considers the soil as a living system, which delivers services. The functioning of this system is mostly carried out by a myriad living organisms that require management and conservation.

Healthy soils are synonymous with sustainability, whereas life cannot thrive in unhealthy soil. Soil health is, therefore, a major contributor to agricultural productivity and sustainability, and indirectly affects human, animal, and plant health. Soil health varies according to the soil characteristics and properties and currently, mainly due to the complex nature of the soil, there is no consensus on what the exact requirement for healthy soil is.

Soil quality refers to the inherent properties of soil, including chemical and physical properties that are intertwined with regional ecosystems and climate. Practices such as mechanical soil cultivation and repeated production of crops on the same soil over many years can cause physical loss of soil through soil erosion. These farming methods also cause loss of organic matter in the soil and the release of CO2 into the atmosphere.

The conservation and maintenance of soil quality are non-negotiable in the quest for sustainable plant production systems, yet it can be a major challenge to develop agricultural systems that sustain high levels of plant production while conserving the land.

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Soil health and quality assessment

Soil health and quality vary across environments, climates and land use management types and can be measured in several ways. Soil organisms are surrogates for soil health and quality because the abundance, diversity and functions of these organisms strongly correlate with the health and quality status of the soil. As the environment and soil properties change, so does soil biology. These biological measures link directly with the abiotic environment in which the organisms live.

Soil organisms also respond to anthropogenic disruption and are indicators of soil ecosystem services. They live in soil and respond sensitively to climate and land management practices. These ecosystem services include contributions to water-holding capacity, decomposition of organic materials, recycling of nutrients, detoxifying toxins and promoting plant health by suppressing pathogenic organisms.

In addition, the organisms that live in the soil also reflect the properties of the soil – their abundance, diversity, community stability, and food web structure are indicators of the status of the soil. As a surrogate for soil health and quality, organisms that live in soil are relatively inexpensive and easy to measure.

For example, earthworms have for many years been used to measure soil health, but the diversity and abundance of nematodes, mites, bacteria and fungi also provide information on soil health, quality and functions. Thus, the measurement of soil organisms is sensitive to disturbance and is correlated with soil function and a reliable indicator of soil health and quality; however, the measurement of soil organisms must follow well-developed sampling protocols and the relevant soil organism’s identification processes.

Soil quality refers to the inherent properties of soil, including chemical and physical properties that are intertwined with regional ecosystems and climate

These organisms reflect land management decisions and ultimately the productivity and health of the plants and animals living off that soil. Indicators of soil health should be easy to understand for those who manage the land and are stewards of soil quality and health.

Assessments of soil health and quality are essential to sustainably managing land. These assessments help identify problems in production areas and help farmers and other land managers link science and practice when assessing the sustainability of their soils. Generally, soil health and quality indicators should assess both the biological (Table 1) and physiochemical (or abiotic) (Table 2) factors that contribute to high-quality and healthy soil.

The list of factors that contribute to soil health (Table 1 and 2) is not all-inclusive and other factors can also contribute to soil health and quality. Yet, this list gives an insight into the requirements of healthy soils and the factors that can be measured to assess whether a given soil is healthy or not.

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Table 1: Biological measures of soil health

Table 2: Abiotic or physiochemical measures of soil health

soil health
Table 2: Abiotic or physiochemical measures of soil health.

Need for holistic approaches

Holistic management approaches that conserve soil as a resource to optimise its multiple functions are needed in support of soil health and quality. Soil health and quality indicators still vary throughout the world and different soil management systems, and the indicators are useful to researchers, but not always to land managers. Consensus on the measurements is needed and the availability of quick, reliable and cost-effective measures of soil health parameters will support farmers and land managers to better manage soils in future.

Strategies for the sustainable management of soil include the conservation of organic matter. This can be achieved through reduced tilling, the use of animal manure, increasing plant diversity and the use of cover crops. Cover crops can also minimise soil erosion. The use of integrated pest and pathogen management strategies, which reduce the reliance on fossil fuels and petrochemicals, will also support biological diversity in soils, which in turn will contribute to healthy and high-quality soil.

Overall, it seems that the challenge of developing comprehensive sustainable soil management systems that will safeguard the health of the soil remains. A better understanding of what soil health and quality are will support decision-makers in the way forward. – Dr Ida Wilson, Science Lead: Organic Products, BioRevolution

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