Effects of reduced tillage and liming on microbial activity and soil properties in a weakly-structured soil

The effects of reduced tillage and lime on crop yield and soil physical and microbial properties were studied in a weakly structured silty clay loam s oil. Two autumn primary tillage practices were compared, mouldboard ploughi ng to 20-25 cm and cultivation to 12 cm. Seedbed preparation was carried ou t by several harrowing operations in the mouldboard ploughed treatment, and with a PTO-driven harrow in the same operation as sowing in the shallow cu ltivation treatment. The tillage treatments were applied alone or were comb ined with liming aimed at soil structural improvement. Lime was added as 6. 5 Mg CaO ha(-1) before the start of the experiment and mixed into the top 1 2 cm of soil with a disc cultivator. A 4-year crop rotation was used: sprin g barley, spring oilseed rape, spring/winter wheat and oats, and all crops were compared each year.:rop residues were retained in the experiment and i ncorporated at cultivation. Aggregate stability was improved by the shallow er tillage depth, probably as an effect of an increase in soil organic matt er and a more active microbial biomass. Liming had little effect on soil st ructure variables but increased microbial activity to some extent. This was reflected in higher crop yields, especially when the shallow tillage depth was combined with liming. Penetration resistance in the seedbed subsoil wa s highest when mouldboard ploughing was carried out in plots without liming . Data were examined with principal component analyses, and the structures in the data were presented as scores and loading plots, which revealed grou pings between samples and relationships between variables, respectively. (C ) 2000 Elsevier Science B.V. All rights reserved.