Effect of crop rotation on the structure of a clayey soil

At the Swiss Federal Research Station for Agricultural Economics and Engineering (FAT) in Tänikon (Switzerland), a field trial was started in 1973 to examine the effects of three crop rotations (G = 60 % cereals, M = 60 % silage maize, V = different crops included 40 % clover grass) and two management intensities (IS = high intensity according to local practice, IP = integrated, moderate intensity) on the structure of a clayey calcaro-gleyic cambisol in a cool and humid climate. Observations within the period of 1990 and 2000 showed in all crop rotations that regular ploughing caused a plough pan which could not even be alleviated within the two years of clover grass in V. In general, a clear dependence of all measured physical soil parameters – especially aggregate stability – on clay and organic matter content was observed. In the topsoil, bulk density and large sized pores varied considerably from year to year as a result of cultivation practices; however, the variation was much smaller in the untilled subsoil. Apart from the bulk density in the topsoil which was highest during the two years of clover grass, the physical soil properties were more favorable in the crop rotation V than in G and M, where more tillage interventions were carried out and, therefore, the soil surface remained uncovered for longer periods. Differences between IS and IP only occurred in years with different soil tillage practices whereas fertilization and plant protection had no influence on physical soil properties. On arable sites with a strong tendency towards the occurrence of plough pans, conventional deep ploughing should be replaced by reduced tillage practices.