ROTHAMSTED STUDIES OF SOIL STRUCTURE .2. MEASUREMENT AND CHARACTERIZATION OF MACROPOROSITY BY IMAGE ANALYSIS AND COMPARISON WITH DATA FROM WATER-RETENTION MEASUREMENTS

Macroporosity (>60 μm) in the three pairs of soils described in Part I was measured and characterized by image analyses. There are significant differences in macroporosity between the soils in each pair, particularly in the subsoil horizons. The results show that the Ragdale, Denchworth and Salop soils are more impervious than those of the Hanslope, Evesham and Flint soils. Comparison of the image analysis results with those derived from air content at 0.05 bar suction shows that in most cases macroporosity by the former is larger. In image analysis the maximum diameter of each pore is measured whereas the water retention method measures the diameter of the smallest exit point of each pore. Differences between the two types of measurement will thus be at a maximum in soils containing many large pores with narrow exit necks. Copyright © 1979, Wiley Blackwell. All rights reserved