Macropore Characterization for Two Tillage Systems Using Resin‐Impregnation Technique

Abstract

AbstractThis study used resin impregnation and image analysis to characterize macroporosity of a Nicollet loam soil (fine‐loamy, mixed, mesic Aquic Hapludoll) under no‐tillage and conventional tillage. Soil samples (7.5 by 5 by 5 cm) were taken at each 5‐cm depth interval to determine macroporosity after conducting solute‐leaching experiments on undisturbed soil columns. These soil samples were impregnated with either polyester or epoxy resin. Impregnated soil blocks were sectioned in the middle and ground to a smooth finish. Photographic slides were made of the horizontal faces and an automatic image analyzer was used to calculate the percentage of area occupied by macropores, and total perimeter, number, and size‐frequency distribution of macropores. Percentage of area, perimeter, and number of macropores were not statistically different for the two treatments. Macroporosity data obtained from the samples did not support the observations made in the solute‐leaching studies on saturated soil columns (i.e., a greater degree of preferential flow in no‐tillage columns) because the air‐dried samples and the saturated columns had different porosity characteristics and because small, two‐dimensional images were unable to sample any less frequently occurring larger pores. Another source of discrepancy between the results of the two studies may be macropore continuity. Two‐dimensional analysis of porosity images does not provide a measure of pore continuity, which can be a decisive factor in solute transport through soil columns under different tillage systems. Results from the resin‐impregnation study were not consistent with the results of a related field study. Inconsistency between the macroporosity data of these two studies were attributed to: the difference in minimum cut‐off diameter of macropores in the two studies, the difference in sample size, and the difference in moisture status of the field and lab samples.