Crop rotation and soil tillage effects observed in a hilly area using simplified crop systems. Note I. Yield of winter crops

摘要

In 1985 a research on crop rotation and soil tillage was started on a hilly area near Bologna, on a clay soil, classified as Inceptysoil Udertic Ustochrepts fine, mixed, mesic, with a prevalence of illite and smectite as clay minerals. In the experiment, which is still in progress, the following crop sequences are compared: 5 biennal rotations of wheat and other cereals (maize, grain sorghum, barley, oat, triticale) and 4 of wheat with industrial crops (sugarbeet, sunflower, soybean, oilseed rape, which was replaced by peas from 1993 onwards); a triticale-oat sequence; continuous crop of wheat, barley, triticale and oat (only until 1993), and the 4-year rotation: sugarbeet-wheat-sunftower-wheat, which, since 1990, was thus modified: sugarbeet-wheat-sunflower-barley. In each rotation the following soil tillage sequences are tested: (a) mouldboard ploughing to 50 cm depth followed, in the next year, by 25 cm ploughing for wheat sowing (ar50/ar25); (b) continuous ploughing to 25 cm (ar25/ar25); (c_1) two layer tillage (chiselling to 50 cm + 10-15 cm rotary hoeing), followed by rotary hoeing (10-15 cm) for winter species in the next year; (c_2) mouldboard ploughing to 25 cm depth for summer species, followed, in the next year, by rotary hoeing (10-15 cm) for winter species. Up to now wheat yield was found to be positively affected by oat and oilseed rape precession. Lower, but still beneficial, effects were observed for barley whilst triticale had null or scarce influence on subsequent wheat production. Yields of winter crops inserted in biennal successions resulted well correlated with weed infestation (mainly wild oat), foot and root fungal disease and barley virus attacks. With reduced tillage all these adversities incresead. Thus minimum cultivation worsened the detrimental effects on cereal yields of monosuccessions and of the 2-year sequences wheat-triticale, wheat-barley and wheat-oat, particularly in the presence of conditions favouring pathogenes and wild oat, respectively. Virus negative effects on yields were not evident in the last year (the 11~(th) and 12~(th) year since the beginning of the experiment), and recently it was less spread in unploughed plots. Tillage responses of triticale and barley were similar to those recorded for wheat, whilst its effects on oat were variable, mainly in relation to wild oat density.