TRAFFIC AND TILLAGE EFFECTS ON SOIL-CONDITIONS AND CROP GROWTH ON A SWELLING CLAY SOIL

Trafficked and non-trafficked (12 m gantry) crop production systems, w hich had been maintained on an Evesham series 60% clay soil since 1986 , were used again in 1993 during the cultivation and sowing of winter wheat. After a one year set-aside break, mouldboard ploughing, tine cu ltivation and rotary digging were compared. Measurements were made of tillage energy, soil tilth, cone penetration resistance, biological ac tivity and crop performance, and on specific plots, soil density, seed bed tilth and water release characteristics. Despite the one year's se t-aside break, the effect of the previously applied traffic treatments remained and resulted in a smaller specific plough resistance and til lage energy on the non-trafficked soil. Tine cultivator draught howeve r was greater on the non-trafficked compared with the trafficked plots . The specific energy required for rotary digging on non-trafficked so il was similar to that required during the ploughing of similar plots. A measure of indefinite biotic activity indicated that this was appar ently greater on the non-trafficked soil, while soil density was decre ased by up to 18% in these conditions compared with the trafficked lan d. Average cone resistance over the depth range 0 to 0.5 m was 1.51 MP a on the trafficked, compared with 1.24 MPa on the non-trafficked soil . Cone resistance also tended to be greater after tine cultivation com pared with that after ploughing. Water release curves were interpreted as showing more macropores within the topsoil of the non-trafficked c ompared with the trafficked plots. Tine cultivation on trafficked soil had more smaller pores than mouldboard plough cultivation. Winter whe at yield was increased by 25% (from 8 to 10 t/ha) on non-trafficked co mpared with trafficked soil.