Abstract

A differential staining procedure was developed to study the degree of association between soil structural form parameters, derived using the SOLICON image analysis system, and the root growth of cotton plants. Under the climatic conditions that prevailed during the experimental period, severe impedance of taproots was associated with a clod width in the range 28 mm to ≥30 mm and a macroporosity value in the range 0.00–0.04 m³/m³. The new root assessment procedure detected soil structural features, for example, well-aerated zones adjacent to near-surface roots in degraded soil not shown by other methods and allowed direct measurement of the proportion of a root’s surface in contact with the soil atmosphere. However, the assessment method should be complemented by direct measurement of the morphology of nearby cotton taproots that have been pulled from the soil. Features that can be assessed include root flatness, the number of lateral roots, root obliquity, and the degree of tapering. In this experiment the lack of flattening in roots pulled from the compacted soil suggested that poor aeration was a bigger problem for the cotton plants than mechanical impedance. Root deformation was not associated with a large decline in lint yield at this site because the crop was irrigated frequently and did not suffer any nutritional stress, and the relatively steep field slope permitted rapid surface drainage.