Determination of soil aggregate porosity using the modified water saturation method

Abstract

The need to find a simple method for measuring soil aggregate porosity (φ) is justified by the growing interest of researchers in this important parameter of soil physical status. The aim of this study was to present a simple method (AM) for estimating the total 0 of a single soil aggregate. In this case, soil aggregate 0 was calculated as the quotient between the pore volume, estimated from the weight of the aggregate saturated with ethanol, and the total volume (VT) of aggregate, calculated from the particle density and dry aggregate weight. The VT estimated with AM was compared with the corresponding volume measured with the photogrammetry (PHM) technique using soil aggregates of 8–16 mm in diameter and collected from three different tillage systems: conventional tillage (CT), reduced tillage (RT), and no tillage (NT). Next, the AM was used to study the effects of the tillage system on soil aggregate φ. Although a strong relationship (R2 = 0.99, P < 0.000 1) between aggregate VT measured with PHM and that estimated with AM was obtained, AM tended to underestimate aggregate VT with an average deviation of 2.85%. This difference may be due to ethanol evaporation during the first 10 s before the ethanol-saturated aggregate was weighed. The use of AM to determine the effects of different tillage systems on aggregate φ showed that this method was sensitive to detect significant differences among the tillage treatments. The results showed that AM could be an accurate, simple, and inexpensive alternative to estimate φ of a single soil aggregate.