Long-term monitoring of microbial biomass, N mineralisation and enzyme activities of a Chernozem under different tillage management

 We investigated the influence of tillage (conventional, minimum and reduced) on selected soil microbial properties of a fine-sandy loamy Haplic Chernozem over a period of 8 years. The microbial biomass and soil microbial processes were affected mostly by type of tillage and to a lesser extent by the date of soil sampling. Whereas xylanase activity was significantly higher in the 0 to 10-cm soil layer of the reduced and minimum tillage systems within the first year of the experiment (protease and phosphatase activities were significantly higher in the second year), significant treatment effects on microbial biomass, N mineralisation and potential nitrification were observed after a 4-year period. The slow response of substrate-induced respiration to the change in type of tillage may have been due to the differences in the biomass C turnover rates. After a 4-year period, the stratification of the soil microbial biomass within the profile of reduced and minimum tillage systems was probably responsible for the more intensive soil microbial processes near the soil surface compared with conventional tillage. In the 20 to 30-cm layer, N mineralisation, potential nitrification and xylanase activity in the conventional treatment were significantly higher than in the minimum and reduced tillage plots due to buried organic materials. Discriminant analysis underlined the similarity of the enzyme activity patterns in the top layer of the reduced and minimum tillage treatments, and in both layers of the conventional tillage system. The trend towards a significant increase in functional diversity caused by reduced tillage became obvious within the first year of the experiment, and this effect was still manifest after 8 years. All relationships suggested that there were differences in available resources (e.g. organic matter) along the sequence of different tillage systems; this was reflected in part by enhanced enzymatic and microbial activities in the soil layers. In conclusion, this study showed that soils affected by tillage may be classified on the basis of their functional diversity. Therefore, the soil microbial properties chosen for microbiological soil monitoring (microbial biomass, N mineralisation and enzyme activities involved in C, N and P cycling) provide a reliable tool with which to estimate early changes in the dynamics and distribution of soil microbial processes within soil profiles. Received: 3 February 1998