Soil health and soil degradation
Questions arose during discussion between SEDA Land and Abertay about the definition of soil health, what degrades soil and what can be done to regenerate and sustain it and the vegetation it supports. An indicator of soil status could be built into the game. Players could choose from among a range of options, practices that ensured a high soil status.
The following is a brief response from Geoff Squire and Lorna Dawson. [In progress, minor editing likely.]
Formation of soil
Soil is formed from (a) bedrock being ‘weathered’ into small inorganic particles, and (b) living things depositing organic matter during their life and when they die. Soil is a mix of this organic and inorganic.
In terrestrial ecosystems most of the organic matter originates from photosynthesis (plants using solar energy to fix CO2 in the air to make their structure). The plants then pass this organic matter to the soil as exudates from roots and as decaying or dead plant structures.
Soil organisms (e.g. bacteria, fungi, invertebrates) then re-work the organic matter into structures that bind the various components of the soil. The binding reducing their loss through erosion, and the pore space that develops allows soil to hold water and nutrients.
In turn, the plants take advantage of the stable soil to anchor their roots and take up what they need to support their growth. There are many criteria for soil health – see soils.org.uk. And a soil scientist Bruce Ball has developed practical guides to assessing a soil’s status – links on the livingfield web at VESS – Visual Evaluation of Soil.
Soil degradation and regeneration
In many parts of the world, the amount of organic matter in soil has decreased leading to mass erosion and loss of productivity. The main bad practices that result in loss of organic matter are severe physical disturbance (e.g. deep, regular ploughing; destruction during harvest of trees), leaving soil bare and exposed to the ‘elements’ for long periods and applying large amounts of mineral fertiliser and pesticide (which mess up the biological processes in soil).
Good practices can counter these by limiting physical disturbance, covering the soil for most or all of the year, and using legume plants to fix nitrogen from the air. In addition, growing mixes of crops, grazing and trees, together in the same field or in sequence, has a general positive effect on soil health.
Crop-grass-tree mixes have a comparable effect on the soil organisms to that recommended for human health, i.e. eat lots of different plant species for a happy gut microbiome.
In the context of a game, there’a need for an indicator of soil or substrate health determined by a few ‘good’ practices and a few ‘bad’ practices, each of which that can be visualised. For example, it should be possible to visualise reduced physical disturbance, ground coverage and plant mixtures.
Good practices
Here are some of the practices used to reduce degradation and to regenerate soil.
- No or minimum tillage: stop or reduce deep intrusive ploughing (examples of hyper-intrusive practices include some modern potato cultivation methods which mince and compact soil)
- Intensification: crops growing in fields as long as possible; covering the ground surface for as long as possible.
- Diversification: smart integration of different crops; including legumes (e.g. peas and beans) for biological N fixation, sometimes in sequence (crop rotation), sometimes mixed in the same field (intercrops, mixed crops); also growing crops such as hemp that produce a lot of organic matter.
- Integrated nutrient management: measuring nutrient status of soil, applying fertiliser where needed, recycling plant matter back to the soil, etc.
- Integrated pest management: reducing pesticide applications to crops and soil – long term effects of high pesticide dosage are still uncertain; instead support organisms that control insect pests, use crop rotation to control weeds, etc.
- Contour ploughing – along contours not up and down slopes.
- In the case of crop-based agriculture, growing ‘grass’ and/or trees with or in sequence with the crops: ‘grass’ (ideally, mixes of grasses, legumes and other plants) generally provides the soil with more stable and long-lived organic matter. Traditionally in Scotland, and to an extent still today, grass is grown for 2-3 seasons in a crop-based rotation (e.g. grass 1, grass 2, oats, barley, peas or beans, turnip, and then repeat). The grass ‘ley’ was known to re-build and stabilise soil.
- Mixed systems with animal manure returns: treating the farm or farms as an integrated unit, e.g. growing grain on one part for food or livestock feed, growing long-term grass on another part, grazing livestock on the grass or crop residues (manure deposited on the soil), using dung to fertilise the crops, etc.
- And in the case of modern forestry practices in Scotland (e.g. growing sitka spruce), using harvesting methods that do not reduce the land back to bedrock. Probably extend this to say that a completely different system of commercial forestry in Scotland is needed – one which builds soil and produces a diversity of high value products.