AN IMAGE-ANALYSIS EVALUATION OF SOIL COMPACTION IN GRASSLAND

In the fifth year of a traffic management experiment on grassland comp aring conventional (C), reduced ground pressure (R) and zero (Z) syste ms, differences in soil structure were characterized in the upper 100 mm. Soil bulk density and vane shear strength increased between system s in the order Z, R, C. A more detailed description of the soil struct ural differences between traffic systems, and between depths within sy stems, was obtained by an image-interpretation technique. Rapid-harden ing epoxy resin, containing fluorescent dye, was added to the soil in the field condition, and the macroporosity was quantified by image ana lysis. 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 sur face 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 conventio nal system. Macroporosity and roots were concentrated close to the soi l surface under the C and R systems. In the absence of traffic, or und er the R system, the surface of the ground was rougher than that under the C system.