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DIVISION S-1 - NOTES

Measurement of soil aggregate density by volume displacement in two non-mixing liquids

^a Facultad de Ciencias Agrarias, Univ. Nacional de La Plata, Calles 60 y 119, CC 31, 1900 La Plata, Argentina
^b Dep. of Environmental Sciences, Rutgers, The State Univ. of New Jersey, 14 College Farm Road, New Brunswick, NJ 08901-8551

* Corresponding author (gimenez{at}envsci.rutgers.edu)

Soil aggregate density is an important property influencing soil biological, chemical, and physical processes. Current methods used to estimate soil aggregate density are based on more or less restrictive assumptions or require specialized equipment. This study was conducted to develop an alternative method for measuring aggregate density of soil and other porous objects that is both simple and theoretically sound. The proposed method solves the balance of forces resulting when a kerosene-saturated aggregate is immersed in a mix of water and glycerin. We tested the accuracy of the method by measuring the volume of 40 aggregates with diameters ranging from 4 to 20 mm and with variable densities. Soil aggregates were saturated in kerosene, drained at a tension of -30 mm, and their volume estimated using a pycnometer. Upon resaturation, aggregates were suspended from a thread and successively weighed in air, in kerosene, and in a mix of water and glycerin. Aggregate volumes and densities varied between 1.20 x 10^-7 and 3.85 x 10^-6 m³ and between 1.05 to 1.86 Mg m^-3, respectively. On average, aggregate volumes estimated with the pycnometric method were 2.6% smaller than the volumes obtained with the proposed technique, suggesting that the new method is less aggressive in evacuating pores open to the surface than a tension of -30 mm. The new method was easier to use, did not require previous preparation of the sample, and was less time-consuming than older methods.