Washington Soil Health Initiative Roadmap

Soils are vitally important to national security, food and nutritional security, water quality and renewability, climate change mitigation and adaptation, human health, and biological diversity (NASEM 2017). Though soils impact human lives in a myriad of ways, agricultural production is perhaps the most direct connection. Land degradation afflicts over a quarter of Earth’s ice-free land (Olsson et al. 2019). In the U.S., agricultural soils have lost as much as 60% of their carbon content over the last century (Lal 2004). Historic farming practices have resulted in compromised soil health in agricultural systems throughout Washington State, as measured by reduced soil carbon and fertility levels, wind and water erosion, soil compaction, increased incidence and severity of soilborne crop disease, and detrimental impacts to air and water quality. It is imperative to prevent (and reverse) land degradation on agricultural soils occurring through soil erosion, nutrient losses, and losses of ecological integrity (IPCC 2019) if the ecosystem services that healthy soils provide (e.g., nutrient holding capacity, water holding capacity, filtration of nutrients and contaminants, food and fiber production) are desired.

Farmers have long known that taking care of the soil is a critical part of crop production. The Dust Bowl era gave rise to an emphasis on minimizing soil erosion (e.g., conservation agriculture), and more recently attention has shifted to rebuilding degraded soil (e.g., regenerative agriculture). Historically, emphasis on soil management for crop production has been focused on managing the chemical (e.g., pH, nutrient levels) and physical (e.g., compaction) characteristics of soil. However, with a growing awareness of the complexity of soil systems there is a better understanding of the critical role of soil biology.

The concept of “soil health” recognizes soil as a dynamic living system and emphasizes the multiple functions of a soil essential to sustaining agricultural production: plant production, nutrient cycling, water storage and availability, and diversity of biological habitats. The USDA Natural Resources Conservation Service (USDA-NRCS) has adopted the description of soil health proposed by Doran et al. (1996) “the continued capacity of soil to function as a vital living system, within ecosystem and land-use boundaries, to sustain biological productivity, maintain the quality of air and water environments, and promote plant, animal, and human health.”

Healthy soils are resilient against disturbances such as flooding, drought, or high winds; support crop production with suitable nutrient, moisture, and physical conditions; support beneficial biological activity that decomposes crop residues, cycles nutrients, forms soil structure, and helps suppress disease; and contribute to environmental sustainability by filtering pollutants and reducing run-off. While the specific characteristics that constitute a healthy agricultural soil are context dependent, they generally include high levels of crop productivity; stable structure; high water-holding capacity, infiltration, and drainage and a level of organic matter that sustains all these; nutrient retention and recycling; the presence of beneficial soil organisms within the microbial community; low populations of plant pathogens and pests; minimal erosion; and an ability to quickly recover from stresses. In contrast, soils that are not healthy have properties that limit crop productivity and are constrained by problems such as erosion, compaction, poor structure, poor water and nutrient retention, and high levels pest pressures (Larkin 2015).

Soil health is assessed by evaluating the soil’s ability to perform desired ecosystem functions and involves measuring soil physical, chemical, and biological indicators in response to changes in management (Awale et al. 2017).