5.1.4—Soil system inputs

Soil inputs can be natural internal recycling, externally transported material or deliberate management additions.

Plant litter, dead animals, manure and decomposition add organic matter; weathering, wind- or water-borne deposition and precipitation add minerals or water; air, gases, humidity and solar energy also cross the boundary. Managed systems add compost, fertilizer, agrochemicals and irrigation, which can also increase salinity.

Compost added to a field is a managed carbon and nutrient input, while leaf fall is a natural seasonal input.

Rainfall and irrigation both add water, but irrigation is a human-controlled input whose timing, dissolved salts and allocation can alter the soil system.

‘Natural’ describes source, not whether the input is beneficial; excess natural sediment can still bury soil.