Soil biology, soil health, and soil carbon

While interest in a more active Northern agriculture grows, the information on Northern agricultural regions suffers from the overall lack of locally relevant data and from a lack of coherent verification of the quality of extant data. This is critical as northern agriculture might take place in microclimatic niches within the region, with unique soil and infrastructural conditions. This gap can only be filled with locally relevant, but a nationally consistent, approach to data collection, verification and implementation. A first step towards a northern solution to Northern crop adaptation through locally relevant plant-soil functions systems is an understanding of the locally relevant soil food webs and phytobiomes. This involves an understanding of soil biota and its functioning and the microbiology along the soil-to-plant continuum. Functions are thus governed by the interrelationship between soil and plants as a continuum of habitats for microbiota and microfauna. To modify functions within this soil-to-plant domain by taxonomic and functional modification of the biological communities, either by introducing preferred (micro)organisms or by their in-situ management directed selection (i.e., through modification in the relevant abiotic conditions), one must understand the governing drivers. Local-resource based management of soils must be verified  and tuned to ensure best functioning of soil biota and microbiota.

Thus, it is argued that stable, functional soil food webs, facilitated by adaptive crops and cropping practices can naturally enhance C sequestration mitigate agriculture’s C footprint, and lower GHG emissions.

Currently, there is no standard indicator or set of indicators of soil quality or sustainability though several countries have developed soil quality assessment approaches. For example, the USA, Canada, and the Netherlands all use national frameworks to assess soil quality yet each of these programs assess different sets of indicators at different spatial scales with different types of land use and managements. SOM, acidity, available phosphorus, water storage, bulk density, available potassium, texture, total N, electrical conductivity, and cation exchange capacity are the top ten most frequently used indicators in soil quality assessments. In addition to these traditional abiotic indicators, biological indicators can be used to quantify sustainability in the face of LULUC and to understand soil quality.

An optimal indicator of soil quality is practical to sample and measure, reliable and cost-efficient, sensitive to changes in soil conditions and management and has a clear interpretation scheme. Biological indicators of soil quality must be meaningful, standardized, measurable and cost-efficient, policy-relevant, validated across spatial and temporal scales, be easily understood, and accurate in describing the changes they monitor. Biological indicators such as microbes and free-living nematodes have a root in the organic farming movement and are, for example, often used across Europe to assess soil quality.

Examples of most often considered biological indicators are:

Soil microbial biomass

Microbial communities (from metagenomics to metabolomics and metatranscriptomics) as indicators of soil functional status

Soil respiration (i.e., the cumulative CO₂ released from below ground plant material by biota, thus an indicator of system decomposition and mineralization while also taking root respiration into consideration

Protozoa

Earthworms (of variable utility given their natural non-uniform distribution and presence across latitudes!) rthworms, along.

(Micro)arthropods (as contributors to nutrient fluxes through the decomposition of OM, regulating microbiomes).

Free-living nematodes (essential to the fluxes of C, nutrients, and energy in soil systems; occupy a range of nodes in the soil food web: bacterivores, fungivores, herbivores, omnivores, and predators and a food source for other fauna. Their measurements might be descriptive of the entire food web functions)