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 Cherno zem over a period of 8 years. The microbial biomass and soil microbial proc esses 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 wit hin the first year of the experiment (protease and phosphatase activities w ere significantly higher in the second year), significant treatment effects on microbial biomass, N mineralisation and potential nitrification were ob served after a 4-year period. The slow response of substrate-induced respir ation 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 ti llage systems was probably responsible for the more intensive soil microbia l processes near the soil surface compared with conventional tillage. In th e 20 to 30-cm layer, N mineralisation, potential nitrification and xylanase activity in the conventional treatment were significantly higher than in t he minimum and reduced tillage plots due to buried organic materials. Discr iminant 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 t illage systems; this was reflected in part by enhanced enzymatic and microb ial activities in the soil layers. In conclusion, this study showed that so ils affected by tillage may be classified on the basis of their functional diversity. Therefore, the soil microbial properties chosen for microbiologi cal soil monitoring (microbial biomass, N mineralisation and enzyme activit ies involved in C, N and P cycling) provide a reliable tool with which to e stimate early changes in the dynamics and distribution of soil microbial pr ocesses within soil profiles.