Complete characterization of pore size distribution of tilled and orchard soil using water retention curve, mercury porosimetry, nitrogen adsorption, and water desorption methods

Abstract

Pore size distribution (PSD) affects numerous soil functions and root growth. The PSD is largely influenced by soil management practices. We have compared the PSD in a wide pore size range of conventionally tilled (CT) and orchard (OR) loamy soil, determined by different methods. Water retention curve, mercury intrusion porosimetry, nitrogen adsorption isotherm and water desorption isotherm were used to quantify the PSD for equivalent pore radii > 50 to 0.1 μm, 7.5 to 0.0037 μm, 0.1 to 0.001 μm and 0.05 to 0.001 μm, respectively. Soil samples were taken from 0–10, 10–20, 20–30 and 30–40 cm depths. The PSD was presented in the form of cumulative pore volume and logarithmically differential pore volume curves with respect to the pore radius. The cumulative curve showed that at depth 0–10 cm the volume of larger pores (> 45 μm radius) was greater under CT soil than OR. However, in deeper layers up to 40 cm, the concentration of the larger pores was greater and that of smaller pores fewer in OR than CT. As shown by the differential pore curve, both OR and CT soil exhibited peaks within textural (primary) and secondary (structural) pore systems. The textural peaks of the pore throat radius (0.0017 μm) as determined by the nitrogen adsorption method were of greater magnitude at depths 20–40 cm than 0–20 cm and at depths 20–40 cm they were more defined under CT than OR. The textural peaks of approximately 1 μm radius were more defined on the PSD from the mercury intrusion porosimetry than water retention curve. The structural peaks in pore radius 70–80 μm were of greater magnitude under OR than CT at all depths. The results show that the approach employing four methods is a suitable tool for characterising a wide range of pore radii influenced by soil management practices.