Impact of different tillage intensities on weed populations in arable crops

In modem cropping systems, there is a tendency to reduce tillage intensity in order to decrease soil erosion, leaching of pesticides and nitrate and p roduction cost. These changes in tillage practices are expected to markedly alter the efficiency of weed control and, thus, weed populations. There is a lack of information on how reduced tillage systems, especially no-tillag e, affect the development of weed populations and the efficiency of weed co ntrol under humid temperate climate, which is typical for large parts of Eu rope. An experiment was conducted on a sandy loam and a loamy silt soil in the Sw iss midlands to investigate the impact of the time of chemical weed control on weed populations in different tillage systems. Pre- and post-emergence herbicides were applied in conventional tillage (CT) with mouldboard plough , minimum tillage (MT) with chisel plough, and no-tillage (NT) in a 'winter wheat - oilseed rape - winter wheat - maize' crop rotation. All crop resid ues were left on the fields and no stubble tillage was done. In this report , data of winter wheat are presented. In winter wheat grown after maize and winter wheat grown after oilseed rape , the density of weed species was significantly affected by tillage systems . The rank order of tillage systems in winter wheat grown after maize and w inter wheat grown after rape was NT < MT < CT and CT < MT < NT, respectivel y. Perennial weed species were more abundant in NT and MT than in CT. Gener ally, the efficiency of postemergence weed control was better than that of pre-emergence weed control.