FACTORS AFFECTING THE TENSILE-STRENGTH OF SOIL AGGREGATES

The influence of water content, organic matter content, aggregate size and the interaction of these factors on the tensile strength of natural aggregates of a sandy loam and of a clay soil were studied. Within the range of conditions studied, which included water contents from field capacity to air dry, tensile strength depended mainly on water content, especially for the sandy loam where organic matter only varied between 1.2 and 3.9%. For the clay soil, with organic matter varying from 1.3 to 10.4%, a large organic matter content appeared to strengthen wet soil aggregates and weaken dry ones. The tensile strength of the smallest aggregates was about 50% higher than the biggest ones. The effect of size was different at different water contents. A knowledge of the interaction was used in an attempt to assess soil friability. However, to relate friability to soil break up during tillage, intermediate matric potentials and a wider range of aggregate sizes are needed.