Temperature effects on C- and N-mineralization from vegetable crop residues

Net N-mineralization and nitrification from soil organic matter and from vegetable crop residues (leaf-blades of cauliflower and stems of red cabbage) were measured at 4 temperatures during aerobic incubation in the laboratory. C-mineralization from leaf-blades of cauliflower was monitored at 3 different temperatures. N-mineralization from soil organic matter was best described by zero order kinetics N(t)=kt whereas N- and C-mineralization from the crop residues were described by single first order kinetics. Stems of red cabbage mineralized much more slowly than leaf-blades of cauliflower. S-shaped functions were fitted to the relationship between the rate constants of both C and N-mineralization and temperature. The rate parameter kappa of the S-shaped function reflects the temperature dependence of the mineralization rate k. The parameter kappa for N-mineralization of the stem material (kappa=5.36) was significantly higher than for the leaf-blades (kappa=3.38), indicating that there is a strong interaction between temperature and resistance to degradation in the soil. N-mineralization from soil organic matter was least sensitive to temperature (kappa=2.63). Temperature dependence of nitrification was not significantly different from mineralization over the temperature range considered. Rate constants for C-mineralization of cauliflower leaf-blades were higher than for N-mineralization, but the temperature dependence of the rate constants was not significantly different for both processes