AN IMAGE-ANALYSIS EVALUATION OF SOIL COMPACTION IN GRASSLAND

In the fifth year of a traffic management experiment on grassland comparing conventional (C), reduced ground pressure (R) and zero (Z) systems, differences in soil structure were characterized in the upper 100 mm. Soil bulk density and vane shear strength increased between systems in the order Z, R, C. A more detailed description of the soil structural differences between traffic systems, and between depths within systems, was obtained by an image-interpretation technique. Rapid-hardening epoxy resin, containing fluorescent dye, was added to the soil in the field condition, and the macroporosity was quantified by image analysis. All measured attributes (bulk density, vane shear strength and those from image analysis) showed that soil structure was superior in the zero (Z) and reduced ground pressure (R) traffic systems compared to that of the conventional (C) system. Porosity and pore or solid surface area of the Z system were greater, and aggregate size was smaller, than in the C system. In general, R was intermediate between Z and C. At about 10-30 mm in the reduced ground pressure system, there was a zone of low porosity that resembled much of the soil in the conventional system. Macroporosity and roots were concentrated close to the soil surface under the C and R systems. In the absence of traffic, or under the R system, the surface of the ground was rougher than that under the C system.