5.1.8—Soil flow diagrams

A useful soil diagram links stores to named inputs, outputs, transfers and transformations for one material and boundary.

Start with water, organic carbon or mineral nutrients; draw arrows with direction and process. Check whether each arrow changes location, chemical form or both.

Leaf litter adds organic carbon and nitrogen to a soil store. Decomposition returns some carbon to the atmosphere as CO2 and mineralizes organic nitrogen into forms plants can absorb; infiltration, uptake and leaching link the same soil boundary to the water and nitrogen cycles.

An auditable arrow names the material, source, destination and process; unlabeled arrows cannot distinguish a transfer from a transformation.

A diagram is not complete because it has many arrows—every arrow needs a defined boundary and mechanism.