Plant residues: composition, decomposition dynamics and C:N balance

Notes

Summary from last lesson Typical Composition of Plants Typical Composition of Plants Compounds Plant Compounds • Carbohydrates are the most abundant – Sugars – Starches – Celluloses • Lignins or phenol structures are components of cell walls – They increase as the plant matures – More abundant in woody plants • Polyphenols e.g. tannins • Lignins and polyphenols are resistant to decomposition Plant Compounds Compounds Decomposability Sugars, starches, simple proteins Rapid decomposition Crude proteins Hemicellulose Fats and waxes Lignin and phenolic compounds Very slow decomposition Rates of Plant Residue Decomposition Kind of material (FAST --> Sugar, starches, proteins --> SLOWER hemicelluloses, cellulose, --> SLOWEST Fats waxes --> lignin • Rate decreases after the easy material has decomposed. Why? • Soil Conditions - water, temp., oxygen, nitrogen, phosphorus, • Decay Products = Energy (heat), carbon dioxide, N,P,S & Humus Decomposition • The breakdown of large organic molecules into smaller, simpler components 1. Enzymatic oxidation of C compounds to produce CO2, water and energy R-CH4 + 2O2 CO2 + 2H2O + energy 2. Release and/or immobilization of essential elements 3. Formatio...