Tillage
The same specially modified, single-furrow, reversible ploughs
were used at both sites, in order to achieve wheel-by-wheel tractor
passes over the whole soil surface each year. Although this
represents a roughly three-fold increase over the normal traffic
intensity associated with ploughing, we considered that total
wheel coverage was necessary each year due to the limited time
available for the study of tractor weight and wheel placement. For
deep ploughing, a Kverneland plough body no. 8 was used, with
disc coulter and skimmer. The depth wheel was set at 25 cm and
furrow width was 40 cm, resulting in semi-inverted furrow slices.
For shallow ploughing, a Kverneland Ecomat plough body was
used, with share knife and skimmer. The depth wheel was set at
15 cm and furrow width was 35 cm, resulting in completely
inverted slices. This difference in slice inversion is a normal
characteristic of these two plough designs. The plough bodies
could be moved laterally on the plough frame to facilitate wheeling
either in the furrow or on-land.