English: Simple conceptual diagram of the carbon, nitrogen, and phosphorus (C,N,P) budgets in the shallow terrestrial subsurface. Organisms recycle nutrients when they degrade organic matter and form new organic compounds. Nutrients can also be added externally or removed from the soil, as indicated. The tree represents plants in general, not just woody vegetation. Root exudates from plants include sugars, amino acids, and organic acids (Canarini et al., 2019). Dust can serve as a major nutrient source for soil, particularly where nutrients have been depleted from the underlying bedrock by intense weathering (Aciego et al., 2017; Pett-Ridge, 2009). Fertilizer inputs include both chemical fertilizers as well as animal wastes. Subsurface transport represents leaching of nutrients and other compounds as water passes through soil. Mineral phosphorus includes primary and secondary phosphate minerals as well as phosphorus that is sorbed to mineral surfaces.