THE DISTRIBUTION OF SOIL COMPACTION WITH DEPTH AND THE RESPONSE OF A PERENNIAL FORAGE CROP

As a result of the great intensity of vehicular traffic to which peren nial forage crops are subjected, the avoidance of long-term induced su bsoil compaction is difficult. The object of this work was to study th e alternatives of using either a light tractor with a high number of p asses or a heavier one with a reduced amount of wheeling on the field. Field tests were carried out on grassland on a Typic Argiudol with a soil moisture below but near field capacity. Three different numbers o f passes, with two tractors with different weights but the same ground pressure, were used to obtain six different traffic intensities. In t he soil profile analysed, ranging from 0 to 600 mm, bulk density and p enetration resistance were measured before and after traffic. Six mont hs later grassland yield was evaluated, both in and out of the vehicle track. Decreases in grass yield ranging from 7 to 25%, were measured in out-of-track areas, and 52 to 76% in intrack areas. If results are compared for the same number of passes, then the heavier tractor appea rs to give either the same or a greater reduction in grassland yield t han the lighter tractor. If the results are compared on a basis of tra ffic intensity, the picture is less clear but it seems likely that the lighter tractor, with a larger number of passes, can do as much or ev en greater damage than the heavier tractor with fewer passes. (C) 1997 Silsoe Research Institute.