Soil biology, soil health, and soil carbon
The challenge
While interest in a more active northern agriculture grows, information on northern agricultural regions suffers from a lack of locally relevant data and from a lack of coherent verification of existing data quality. This is critical, because northern agriculture may take place in microclimatic niches with unique soil and infrastructural conditions – a gap that can only be filled with a locally relevant, but nationally consistent, approach to data collection, verification and implementation.
A first step toward a northern solution for crop adaptation, through locally relevant plant-soil function systems, is an understanding of the soil food webs and phytobiomes: the soil biota, its functioning, and the microbiology along the soil-to-plant continuum. Functions are governed by the interrelationship between soil and plants as a continuum of habitats for microbiota and microfauna. To modify these functions – by introducing preferred (micro)organisms, or through in-situ, management-directed selection (i.e. by modifying the relevant abiotic conditions) – one must understand the governing drivers. Local, resource-based soil management must be verified and tuned to ensure the best functioning of soil biota and microbiota.
Key insight
Stable, functional soil food webs, facilitated by adaptive crops and cropping practices, can naturally enhance carbon sequestration, mitigate agriculture’s carbon footprint, and lower greenhouse-gas emissions.
Assessing soil quality
There is currently no standard indicator, or set of indicators, of soil quality or sustainability – though several countries have developed assessment approaches. The USA, Canada and the Netherlands each use national frameworks, yet each assesses different sets of indicators, at different spatial scales, across different land uses and management. The ten most frequently used indicators are: soil organic matter, acidity, available phosphorus, water storage, bulk density, available potassium, texture, total nitrogen, electrical conductivity, and cation-exchange capacity.
Beyond these traditional abiotic measures, biological indicators can quantify sustainability in the face of land-use and land-cover change (LULUC) and help us understand soil quality. An optimal indicator is practical to sample and measure, reliable and cost-efficient, sensitive to changes in soil conditions and management, and comes with a clear interpretation scheme. A good biological indicator must be meaningful, standardized, measurable, cost-efficient, policy-relevant, validated across spatial and temporal scales, easily understood, and accurate. Microbes and free-living nematodes – rooted in the organic-farming movement – are, for example, widely used across Europe to assess soil quality.
Biological indicators of soil quality
Most often considered
- Soil microbial biomass.
- Microbial communities (from metagenomics to metabolomics and metatranscriptomics) as indicators of functional status.
- Soil respiration – the cumulative CO₂ released from below-ground plant material by biota; an indicator of decomposition and mineralization that also accounts for root respiration.
- Protozoa.
- Earthworms – of variable utility given their naturally non-uniform distribution and presence across latitudes.
- (Micro)arthropods – contributors to nutrient fluxes through the decomposition of organic matter, regulating microbiomes.
- Free-living nematodes – essential to the fluxes of carbon, nutrients and energy in soil; they occupy a range of food-web nodes (bacterivores, fungivores, herbivores, omnivores and predators) and are a food source for other fauna, so their measurement can describe whole food-web function.