SOIL AND CROP RESPONSES TO DIFFERENT TILLAGE SYSTEMS

An experiment was carried out over eight consecutive years at three sites, on clay or clay loam soils. In a split-plot design, two main treatments (mouldboard ploughing to 25 cm depth and disc or springtine cultivation to 13 cm depth) were combined with two seedbed preparation treatments (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 layer shallow cultivation resulted in significantly higher bulk density, degree of compactness and penetration resistance, and lower root density than in mouldboard ploughing. A reduced number of tractor passes achieved by using the PTO driven harrow resulted in significantly lower bulk density and penetration resistance in the unploughed soil, while still providing an adequate seedbed. At 25-30 cm depth, the volume of pores with equivalent diameter > 100 mum, saturated hydraulic conductivity 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 concentration of organic carbon and potassium in the upper 13 cm. Phosphorus distribution and pH were not altered by the tillage systems. The yield was improved by the PTO driven harrow both in ploughed and unploughed plots.