A handful of healthy soil is teeming with life. The billions of organisms, bacteria, and fungi that live and work in soil are responsible for what can almost be considered the basis for life on earth. Put another way, these organisms decompose dead plants and animals to release nutrients for future uptake by plants— and a step further up the food chain— for uptake by animals and humans once they have eaten the plants. This natural process of cycling nutrients creates vital material known as soil organic matter (SOM), the origin of plant nutrition.
Ultimately, healthy soil is crucial for maintaining Earth’s ecosystems. A working group established by the Soil Science Society of America defined soil health as “the continued capacity of soil to function as a vital living system…to sustain biological productivity, maintain the quality of air and water, and promote plant, animal, and human health.”
How Does Healthy Soil Impact Human Health?
Today’s renewed interest in the soil-human health connection comes from the modern ‘One Health’ concept that links human health to the health of the soil. SOM is crucial in providing nutritious food to humans because it assists micronutrient uptake through what is called the chelation effects of SOM. Chelation is a process that increases the absorption of nutrients rather than allowing for nutrient loss through excretion.
Unfortunately, the nutrient content in plant-based food is being reduced by the so-called dilution effect—where increases in fertilizer and water lead to higher yields but poorer nutritional quality of individual crops. In order to supplement traditional approaches to nutrition-enhancement—nitrogenous fertilizer, irrigation, and other energy-intensive inputs—emphasis is shifting now to the role of rhizospherical microbes that lurk near the root microbiome of plants.
Scientists are studying the services that rhizosphere bacteria provide, such as the promotion of plant growth and the immobilization of heavy metals in the soil. Research has shown that long-term overuse of chemical inputs acidifies the soil and reduces the diversity of these important microbes.
Can the Right Soil Provide More and Healthier Food—on Less Land?
Our growing global population requires an increase in the quantity and nutritional quality of food. Rather than expanding agriculture’s share of finite global lands, increases in crop production can be better achieved by restoring soil functionality and reducing land area under cultivation. It is in this context that building up the SOM content of degraded and depleted agricultural land is an important strategy.
Increasing SOM also grows soil organic carbon (SOC) stock. SOC—about 50% of the SOM—is depleted from agroecosystems by erosion, mineralization, and leaching. Accelerated erosion by water and wind transports SOC laterally along with clay and finer materials. The SOC removed by erosion is transferred to the hydrosphere (including oceans, rivers, and clouds) and atmosphere with adverse effects on ecosystem services.
Improving soil health promotes consistent and nutritious yields while also aiding carbon sequestration and reducing erosion.
Rather than focusing on the impact of SOM on maximizing crop yields, looking at its effects on maintaining a consistent yield—especially under stressed seasons of low rainfall—and nutritious food should provide a better framework for soil management.
One important tool for achieving consistent, quality yields is site-specific SOM management. There are over 300,000 global soil series—areas with distinctly different soils—therefore, site-specific relations must be established between SOM content and crop yield. Positive effects of SOM content on crop yield have been reported by several researchers.
Crop yield and SOM content are mutually reinforcing phenomena: increase in crop yield enhances SOM content and vice versa. Because of numerous and complex interacting factors, it is critical—and difficult—to establish a direct cause-effect relationship between crop yield and SOM content. Nonetheless, available data indicate that all other factors being equal, soils with high SOM content have high yields.
Addressing Key Farming Challenges Now and for the Future
Fertilizer use-efficiency: The overuse and inefficient use of fertilizer has severe impacts on soil and ecosystem health. Additionally, producing and applying excessive volumes of fertilizer wastes a tremendous amount of energy. In the US, fertilizer use-efficiency is only about forty percent. Attention and resources are needed to engage chemical engineers to develop better solutions that are not immediately soluble and will minimize degradation and pollution.
Region-by-region yield gap: Across the world, there are significant discrepancies between regional crop yields caused by limited understandings of best practices. Knowledge-sharing initiatives with national-level support are one strategy to improve yields. Dr. Lal led a 1971 study in Nigeria that produced a five-fold yield increase by incorporating no-till methods and core residue mulching.
Food for megacities: There are currently twenty-eight megacities in the world with the city of Lagos, Nigeria, projected to reach a population of ninety-three million by 2100. Producing food within city limits for the local people is a key need in these locations. Urban farming, home gardening, even growing a few tomato plants in pots, will help. Developing means to safely and hygienically recycle nutrients that enter the city and waste produced within will be an important advancement.
Plant-based diet: It is important to consider responsible strategies for feeding a projected population of eleven billion people with a healthy diet. The nutrients, water, and land required for animal-based protein production are much higher than those required for plant-based protein. Relying on the prevalent animal-based diet requires careful reconsideration. Plant-based diets have notable health benefits and are more environmentally sustainable.
Supporting farmers to promote soil health: Farmers and land managers are the front-line actors in charge of how soil is maintained. Incentive schemes are one possible policy that can be used to encourage investment in best practices to build SOM. To this end, it would be necessary to develop methods of monitoring and modeling soil health under field conditions that farmers and policy makers can relate to and understand.
Harnessing Waste is Critical for Soil Health
In nature, there is no such thing as waste. You can use what we call waste, whether it is animal or agricultural, to produce energy or to convert it into humus or compost for enhancing the soil. Soil dies when we take away the so-called waste (corn stalks or wheat chaff, for instance) that serves as food for soil-friendly organisms that convert it into SOM to feed healthy plants.
Enhancing SOM content is the critical strategy for making soil and agriculture important solutions to the environmental problems of the twenty-first century.
*Rattan Lal, Ph.D., is a distinguished professor of Soil Science in the School of Environment and Natural Resources and director of the CFAES Rattan Lal Center for Carbon Management and Sequestration at The Ohio State University.