Biological activity and organic matter mineralization of soils amended with biowaste composts

This study aims to elucidate the significance of compost and soil characteristics for the biological activity of compost-amended soils. Two agricultural soils (Ap horizon, loamy arable Orthic Luvisol and Ah horizon, sandy meadow Dystric Cambisol) and a humus-free sandy mineral substrate were amended with two biowaste composts of different maturity in a controlled microcosm system for 18 months at 5°C and 14°C, respectively. Compost application increased the organic matter mineralization, the C_mic : C_org ratio, and the metabolic quotients significantly in all treatments. The total amount of C_org mineralized ranged from < 1% (control plots) to 20% (compost amended Dystric Cambisol). Incubation at 14°C resulted in 2.7- to 4-fold higher cumulative C_org mineralization compared to 5°C. The C_mic : C_org ratios of the compost-amended plots declined rapidly during the first 6 months and reached a similar range as the control plots at the end of the experiment. This effect may identify the compost-derived microbial biomass as an easily degradable C source. Decreasing mineralization rates and metabolic quotients indicated a shift from a compost-derived to a soil-adapted microbial community. The C_org mineralization of the compost amended soils was mainly regulated by the compost maturity and the soil texture (higher activity in the sandy textured soils). The pattern of biological activity in the compost-amended mineral substrate did not differ markedly from that of the compost-amended agricultural soils, showing that the turnover of compost-derived organic matter dominated the overall decay process in each soil. However, a priming effect occurring for the Dystric Cambisol indicated, that the effect of compost application may be soil specific.