To build soil organic carbon, the supply of organic matter inputs, particularly legumes (through plant leaf and root residues and root exudates) must be greater than the loss of organic matter through microbial decomposition, leaching and erosion. Soil nutrients, particularly nitrogen, must also be in sufficient supply to aid sequestration of stable soil organic matter via microbial decomposition.

Increasing the clay content of sandy soils, through soil modification techniques such as clay spreading and delving, or inputs of composts/manures/biochars, may also have the potential to improve the amount of carbon held in the soil.

Future challenges

Further research is required to fill significant knowledge gaps, provide a better understanding of the soils that have the greatest potential for carbon improvement, and establish the likely impact of a drying climate on long term soil carbon levels.

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Managing to enhance soil carbon
Intercropping with legumes should enhance stable soil organic carbon and soil health. (Source: Ian and Fiona Koch, Moculta SA)