SOIL AND CROP RESPONSES TO DIFFERENT TILLAGE SYSTEMS

An experiment was carried out over eight consecutive years at three si tes, on clay or clay loam soils. In a split-plot design, two main trea tments (mouldboard ploughing to 25 cm depth and disc or springtine cul tivation to 13 cm depth) were combined with two seedbed preparation tr eatments (three passes with a conventional harrow vs. one pass with a power take off (PTO) driven harrow). Seedbed characteristics-and bulk soil properties investigated at one of the sites in 1991 were similar in the different treatments in the 0-13 cm layer. In the 13-25 cm laye r shallow cultivation resulted in significantly higher bulk density, d egree of compactness and penetration resistance, and lower root densit y than in mouldboard ploughing. A reduced number of tractor passes ach ieved by using the PTO driven harrow resulted in significantly lower b ulk density and penetration resistance in the unploughed soil, while s till providing an adequate seedbed. At 25-30 cm depth, the volume of p ores with equivalent diameter > 100 mum, saturated hydraulic conductiv ity and air permeability were higher with ploughless tillage than with conventional tillage. Pore continuity was greater in unploughed soil at all depths investigated. In unploughed plots there was a concentrat ion of organic carbon and potassium in the upper 13 cm. Phosphorus dis tribution and pH were not altered by the tillage systems. The yield wa s improved by the PTO driven harrow both in ploughed and unploughed pl ots.