A Rapid Method for Analysis of Soil Macropore Structure. I. Specimen Preparation and Digital Binary Image Production

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Abstract
Previously the use of direct observation of soil pore structure in assessing tillage trials has been restricted by the slowness of specimen preparation and data generation. It is desirable that pore structure assessment be performed within a similar time‐scale required for other routine chemical and physical measurements. This would aid the interpretation of routine measurements and enhance the ability to make management decisions in the same growing season as sampling. A method developed for rapid analysis of soil pore structure is presented in two parts. In this paper, a new technique for production of an undisturbed planar face through soil with pore space in the field condition is described. Field impregnation with opaque epoxy resin, that will cure in moist soil, is followed by sawing, laboratory impregnation of the exposed face, and grinding back beyond the original surface to a smooth finish. Grinding is followed by digitization, and digital grey‐level image segmentation to produce a binary image. Methods of image production are described, explained, and illustrated. Samples of Vertisols from a tillage and fallow management trial are shown as examples of the technique. The method can be completed in 4 d for a single specimen. It is emphasized that high quality binary images should be used for image measurement. The discipline of mathematical morphology is used to ensure this quality. This paper finishes with production of high quality digital images that provide graphic illustration of the nature of the pore structure in the vertical plane under the different tillage treatments.