Healthy soil is the foundation for healthy crops and profitable agricultural systems and insights into soil health will help in a profitable agricultural production system. As soil is a natural resource where plant roots and microbiota bind with mineral nutrients, regulating soil aeration, water, and nutrition, soil health is of utmost importance because it sustains the agricultural systems and protects natural ecosystems.
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Soil is a complex environment that sustains plants, animals, and humans. Along with plants and animals, soil also provides a home to millions of microbial communities. These microscopic entities greatly contribute to soil health and its ecosystem. Soil serves as a medium for plant growth and development. It is a system of water supply, nutrient recycling, and decomposition of organic matter. In addition to that, soil is a provider of 98.8% of food to humanity. Therefore, soil health is one of the most important factors when considering food security as well as soil leading to the foundations of sustainable agriculture.
According to Doran and Walsh (1996) soil health is "the continued capacity of soil to function as a vital living system, within an ecosystem and land-use boundaries, to sustain biological productivity, maintain or enhance the quality of air and water, and promote plant, animal and human health”. Simply put, soil is a multifunctional system that serves the ecosystem with a wide range of services.
Soil Services to Humankind
Soil is a great component of the natural ecosystem and provides tremendous services. These services ultimately fulfill the needs of humankind including the provision of food, fiber, wood, and the alleviation of the climate impacts. Soil is also responsible for the recycling of nutrients through its local microbiota.
Soil as a Source of Food and Fiber
One of the most important services of soil to humanity is the provision of food and fiber as soil provides physical support to plant roots and nutrition. Soil microbial communities help to promote plant growth and development. These microbes also prevent plants from pathogenic microbes which eventually contributes to the production of food.
Soil as a Habitat for Millions of Microbes
A wide variety of microbial communities inhabit the soil. This soil microbiota plays a vital role in soil and plant health as the microbes help to decompose soil organic matter (SOM) and maintain plant nutrition such as plant growth-promoting rhizobacteria (PGPR) and arbuscular mycorrhizal fungi (AMF). These microbes do not only maintain plant growth but also accumulate beneficial microbiota at the plant root zone.
Soil as a Provision of Biofuels (Energy)
Another important service of soil is the provision of biofuel. These biofuels are produced from sugarcane, maize, canola, soybean, and rapeseed. However, the use of soil for biofuels requires proper care and examination to circumvent the impacts of intensive practices for higher production.
What are the Factors that Deteriorate Soil Health?
Extreme weather conditions and agricultural intensification are factors that contribute to soil health deterioration. These factors disrupt the functional profiles of soil's beneficial microbes thereby impairing the soil's natural ecosystem as well as damaging the soil's services to humanity.
Agricultural intensification damages soil health unsustainably. According to the FAO, in 2015 almost 33% of soil is degraded due to the excessive application of agrochemicals, erosion, and contamination. If soil degradation continues, it will reduce food productivity by 12% and increase food prices by 30%.
Intensive agricultural practices are employed to obtain higher crop yields with minimum inputs. Intensive agricultural systems involve the production of diverse crops with similar cultivation methods whilst using agrochemicals (pesticides, fertilizers, and agricultural machinery). These chemical applications with similar cultivation methods favor the homogenization of agricultural land thus harming the diversity of soil.
Soil Degradation due to Excessive Application of Agrochemicals
Agrochemicals such as fertilizers are applied to achieve maximum crop yields, and the application of these synthetic nutrients helps farmers to yield higher productions regardless of soil health. It is estimated that up to a 30 - 50% increase in crop yield has been achieved through nitrogen fertilizers. However, the excessive application of nitrogen fertilizers not only decreases their efficiency in the agriculture production system. But also causes the loss of nitrogen into the environment and soil.
The over-application of nitrogen fertilizer acidifies the soil and damages its physical structure. The higher levels of nitrogen also contribute to the emission of nitrous oxide—a greenhouse gas. Therefore, the excessive amounts of nitrogen in soil not only impacts the soil's production capacity but also impacts the environment through greenhouse gas emissions.
Soil Degradation due to Contamination
Soil becomes contaminated due to various agricultural cultivation methods. One such example is irrigation water. The irrigation water may be contaminated with fertilizers, pesticides, and industrial chemicals. The use of contaminated water for irrigation contaminates the soil and as a result, alters the composition of soil microbiota whilst depriving the soil of its nutrients and beneficial microbes.
Soil Health Improvement
The well-being of soil depends on agricultural management practices. For example, the practices that involve the reduction or reversing of soil degradation. These are contour plowing, zero tillage, and cover crops. Healthy approaches improve soil nutrition through nutrient storage. Soil organic matter (SOM) plays an important role in soil health as soil organic matter enhances microbial activity and adds nutrients to the soil.
Cover crops benefit the soil in terms of health and crop productivity. These crops protect the soil during heavy rains, wind, and erosion as well as enhancing the soil's organic matter and preventing nutrient leaching. Legume cover crops retain nutrients and add nitrogen to the soil through nitrogen fixation.
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