Soil health critical for maintaining human health, biological diversity, researchers say

A farm in Mwala, Kenya. ICRAF/Kelvin Trautman

Healthy soil sustains life on Earth, channeling nutrients through plants, supporting essential water and land-based systems, absorbing carbon dioxide to fight climate change – yet most of us walk all over It without a thought.

However, with the theme “Keep soil alive, Protect soil biodiversity,” World Soil Day on Saturday is a reminder of the vital importance of restoring and sustaining soil health against degradation by winds, sun, harsh land use and farming practices that deplete nutrients.

The deep value of soil health is already acknowledged by global leaders,  featuring prominently in many key international conventions and programs. The U.N.’s Sustainable Development Goal 15, for example, urges numerous measures for soil protection. Restoring and rehabilitating degraded ecosystems and soil function for sustainable production and food security is highlighted by the U.N. Food Systems Summit in 2021.

This year, the key role of soil featured prominently on the global stage when expert Rattan Lal, who introduced innovative conservation agriculture techniques, became the latest winner of the prestigious World Food Prize, which is known as the “Nobel for food.”

Almost all the world’s food is produced in soil – directly or indirectly – yet an estimated 40 percent of it is degraded. The U.N. Decade on Ecosystem Restoration, which begins next year emphasizes the necessity of revitalizing the land, rebuilding its organic carbon stores and the micro-organisms that soak up water and maintain soils.

“There is a strong link between soil health and human health,” said Leigh Winowiecki, a soil systems scientist and Soils Theme leader at World Agroforestry (ICRAF). Just as human skin envelops and protects the human body, soil provides the Earth’s protective covering, said Winowiecki, who led a five-year soil restoration project working with farmers in arid parts of eastern Kenya, Niger, Ethiopia and Mali.

Farmers there, supported by ICRAF scientists, have integrated practices designed to reduce erosion and increase carbon and other biological materials in severely degraded soil to boost productivity while adding other ecosystem services.

“We identified the fact that soil erosion was very high and soil organic carbon levels were very low, and worked with farmers to develop locally appropriate restoration options,” Winowiecki said. For example, in eastern Kenya, to reduce erosion and nourish their soil, smallholder farmers worked the soil into basins instead of plowing their land into rows; then, applied composted manure and mulch to return organic material into it. Through the project, farmers benefitted from innovative agroforestry and crop diversification techniques, using these as an effective way to increase food security.

Farmers also planted some 30,000 trees across three countries during the project and found that by integrating trees and crops, and by implementing tailored soil-water conservation measures, yields were increased by two to six times the usual amount. Over the long term, the benefits of these techniques will make farmers and the land more resilient to the impacts of climate change, erosion, floods and droughts.

In addition to such innovative agroforestry practices, ICRAF, with partners, has developed innovations in soil analytics, including soil spectroscopy. In the ICRAF-hosted Soil-Plant Spectral Diagnostics Laboratory in Nairobi, light is used to measure the physical and chemical properties of enormous numbers of soil samples rapidly and inexpensively, creating the world’s largest geo-referenced library of the planet’s soil.

This includes measurements of soil organic carbon (SOC), which is a key indicator of soil health, due to its influence over numerous aspects of soil – such as soil’s ability to release minerals such as magnesium, potassium, and calcium which plants can then absorb and share with humans.

This SOC also Influences hydrologic cycles, including the land soil’s ability to infiltrate, absorb and store water; and holds the promise of providing a potent tool for climate change mitigation, Winowiecki said. Her research has indicated that managing soil erosion is a key strategy for reducing SOC loss and hence, supporting climate change mitigation and adaptation in affected landscapes.

“Feeding the soil by increasing carbon through the addition of organic amendments or promoting permanent coverage of the soil by integrating legumes in cropping systems, has the potential to increase the abundance and diversity of soil biota that are key to delivery and amplification of agricultural-related ecosystem services,” said Ebagnerin Jérôme Tondoh, associate professor in agro-ecology and soil ecology at Ivory Coast’s Nangui Abrogoua University in Abidjan and seconded Land Health Scientist at ICRAF.

Tackling soil erosion can also require reviewing farming techniques, as demonstrated by the eastern Kenya soil restoration project Winowiecki leads. “We know that soil has a huge potential to store carbon; however, unsustainable farming practices have decreased the original carbon pool by up to 50 percent, in some cases,” she said.

The use of robust soil sampling frameworks – such as ICRAF’s Land Degradation Surveillance Framework (LDSF) –  coupled with soil spectroscopy and cutting-edge data analysis has enabled landscape-scale assessments of key indicators of soil health, including soil organic carbon. By combining these with data from remote sensing platforms using predictive models, soil properties can be mapped across landscapes.

That, for example, can help to assess very specific soil and land health factors, such as levels of soil erosion, or the chemical composition of soils, including acidity levels. This is critical knowledge for restoration planning as well as assessments of existing projects.

“We need to understand the soil better, including its variability across spatial scales,” said Winowiecki. “Ultimately, we need to understand the role of healthy soil for agricultural productivity; the role of soil for achieving landscape restoration; and as a result, help in better and more holistic soil management. We believe that advances in soil analytics using novel methods, such as soil spectroscopy, combined with cutting-edge data science, represent huge future opportunities.”