Little conclusive evidence was found to support the use of onland
rather than in-furrow wheeling during ploughing, in terms of
its effect on soil structure and yields, provided that ploughing is
performed at or below field capacity, with tyre inflation pressures
at or below 80 kPa and in the absence of wheel-slip. There is,
however, reason to be wary of using heavy tractors (>5 Mg), even
under such conditions. Such tractors negatively affected topsoil
structure and yield levels in some cases, but their effect on subsoil
properties was probably slight in these trials. With regard to
ploughing depth in organic cropping systems dominated by
cereals, the need to combat perennial weeds by deep ploughing
weighs probably at least as heavily as any possible beneficial effect
of shallow ploughing on stimulating nutrient turnover