EFFECTS OF CONVENTIONAL AND MINIMUM TILLAGE ON WINTER OILSEED RAPE (BRASSICA-NAPUS L) IN A SANDY SOIL

A 3-year (1986-1988) comparison between conventional (CT) (25 cm deep ploughing) and minimum (MT) (10-15 cm deep disk harrowing) tillage was carried out in southwest Tuscany on a very sandy soil (Typic Xeropsamment) where oil rapeseed was cultivated. The CT plots showed a greater water retention capacity in the deeper horizons than the MT plots. Moreover CT was characterized by a quicker water rate of depletion in the upper soil layers when evapotranspirative demand was high. The bulk density and penetration resistance of the ploughed soil, measured to 30 cm depth, were less under CT than under MT, The presence of subsurface compacted soil layers as the result of continuous MT caused a progressive worsening of soil conditions for plant root growth and, consequently, a reduction of root system mass and tap-root length compared with the ploughed plots. However, rapeseed grain and biomass yields under CT and MT never differed significantly. Finally, MT use was connected with remarkable reductions (55% on average) of working time, fuel consumption, energy requirement and cost when compared with CT.