MICROBIAL BIOMASS AND ACTIVITY OF A RECLAIMED-POLDER SOIL UNDER A CONVENTIONAL OR A REDUCED-INPUT FARMING SYSTEM

The size and activity of the microbial biomass were measured during 3 yr in two fields. One field was cultivated as a reduced-input farming system, the other as a conventional system. In the top 25 cm the size and activity of the biomass were greater in the reduced-input field. Below a depth of 40 cm no differences were apparent. There were still substantial amounts of biomass and considerable microbial activity to a depth of 1 m. Compared with the field treated as a conventional system, the relative increases in total N, N flush and N-mineralisation rate in the reduced-input field were greater than the relative increases in organic C, microbial biomass C and C respiration. In the case of C, the relative increases in the reduced-input field were greater for microbial activity (respiration) than for organic C and microbial biomass C. Microbial biomass decreased with increasing soil moisture stress and increased strongly after remoistening of the soil.