Effect of temperature on the mineralization of C and N of fresh and mature compost in sandy material

Information about the mineralization rate of compost at various temperatures is a precondition to optimize mineral N fertilization and to minimize N losses in compost-amended soils. Objectives were to quantify the influence of the temperature on the mineralization rate and leaching of dissolved organic carbon (DOC) and nitrogen (DON), NO3-, and NH4+ from a fresh (C : N = 15.4) and a mature (C : N = 9.2) organic household waste compost. Compost samples were mixed with quartz sand to ensure aerobic conditions, incubated at 5, 10, 15, 20, and 25 degreesC and irrigated weekly for 112 days. For the fresh compost, cumulative CO2 evolution after 112 days ranged from 36% of the initial C content at 5 degreesC to 54% at 25 degreesC. The CO2 evolution was only small in the experiments with mature compost (1 to 6% of the initial C content). The data were described satisfactorily by a combined first-order (fresh compost) or a first-order kinetic model (mature compost). For the fresh compost, cumulative DOC production was negatively related to the temperature, probably due to leaching of some of the partly metabolized easily degradable fractions at lower temperatures. The production ratios of DOC : CO2-C decreased with increasing temperature from 0.094 at 5 degreesC to 0.038 at 25 degreesC for the fresh and from 1.55 at 5 degreesC to 0.26 at 25 degreesC for the mature compost. In the experiments with fresh compost, net release of NO3- occurred after a time lag which depended on the temperature. Cumulative net release of NO3- after 112 days ranged from 1.8% of the initial N content at 5 degreesC to 14.3% at 25 degreesC. Approximately 10% of the initial N content of the mature compost was released as NO3- after 14 days at all temperatures. The DOC : DON ratios in the experiments using fresh compost ranged from 11.5 to 15.7 and no temperature dependency was observed. For the mature compost, DOC : DON ratios were slightly smaller (7.4 to 8.9). The DON : (NH4+ + NO3-) ratio decreased with increasing temperature from 0.91 at 5 degreesC to 0.19 at 25 degreesC for the fresh compost and from 0.21 at 5 degreesC to 0.12 at 25 degreesC for the mature compost. The results of the dynamics of C and N mineralization of fresh and mature compost can be used to assess the appropriate application (timing and amount) of compost to soils.