This is, in many ways, the easiest method with the most instantaneous results. There are three main types of organic matter that can be added:
- Green organic matter - e.g. green manures
- Brown organic matter - e.g. compost and manures
- Black organic matter - e.g. biochar
It's important to also have a cultivation strategy that minimises losses, if adding organic matter in to a cultivated system.
Due to their nature, perennial cropping systems rarely involve cultivations, which is a major cause of soil carbon loss. They come in several categories:
- Pastures - e.g. grasses, clovers, etc.
- Trees - e.g. fruit, nut, timber
- Soft and vine fruits
- Energy crops - e.g. miscanthus, willow
Some of these can be integrated with other systems too - agroforestry, maximising the benefits to both systems.
Biologically active soils are more efficient at converting organic matter in to more stable forms of soil carbon and storing it deeper in the soil profile, ensuring it is less easily oxidised. Furthermore aggregate stability is increased where more soil microbial life is found, therefore reducing soil erosion and improving structure. As micro-organism levels build in healthy soils, their ability to decompose organic matter and create humus increases over time. The soil's ability to absorb organic matter also increases; whilst degraded soils that become well managed will grow at the fastest rates, all soils can continue to build organic matter.
Biologically active soils can be enhanced by:
- Regular supplies of organic matter
- Minimal cultivations
- Minimal compaction and/or poaching
- Introduction of beneficial bacterial or fungal innoculants where necessary
Rotating annual crops
A sustainable crop rotation for annual crops is an essential strategy for a soil carbon-friendly cultivation strategy. Ideally a sustainable crop rotation would include:
- A range of crops from different family groups
- Different rooting depths
- Different cultivation requirements
- Include medium to long term (2-5 years) green manures if possible
Read Rob Richmond's Nuffield report on building soil carbon