Extraction of compounds associated with water repellency in sandy soils of different origin

Abstract

After an initial evaluation of several solvents, the efficiency of Soxhlet extractions with isopropanol/ammonia (s.g. 0.88) (70 : 30 v : v; 24 h) in extracting compounds associated with water repellency in sandy soils was examined using a range of repellent and wettable control soils (n = 15 and 4) from Australia, Greece, Portugal, The Netherlands, and the UK. Extraction efficiency and the role of the extracts in causing soil water repellency was examined by determining extract mass, sample organic carbon content and water repellency (after drying at 20°C and 105°C) pre- and post-extraction, and amounts of aliphatic C–H removed using DRIFT, and by assessing the ability of extracts to cause repellency in acid-washed sand (AWS). Key findings are: (i) none of organic carbon content, amount of aliphatic C–H, or amount of material extracted give any significant correlation with repellency for this diverse range of soils; (ii) sample drying at 105°C is not necessarily useful before extraction, but may provide additional information on extraction effectiveness when used after extraction; (iii) the extraction removed repellency completely from 13 of the 15 repellent samples; (iv) extracts from all repellent and wettable control soils were capable of inducing repellency in AWS. The findings suggest that compounds responsible for repellency represent only a fraction of the extract composition and that their presence does not necessarily always cause repellency.

A brief overview of the causes, impacts and amelioration of soil water repellency - a review

“…Capriel (1997) suggested using Diffuse-Reflectance Infrared Fourier Transform (DRIFT) Spectroscopy to detect hydrophobic compounds in soil. Again, links between DRIFT and actual measurements of water repellency are unconvincing (Doerr et al 2005).…”

Eucalyptus reforestation induces soil water repellency

“…Humic material generally consists of a mixture of large, aromatic-based polymers with phenolic and carboxylic functionality capable of interacting with the surface of soil particles. Alternatively, several studies (Franco et al 2000;Doerr et al 2005;Mainwaring et al 2013) investigated the contribution of waxcontaining compounds and particles to the development of water repellency in soils. They suggested that the main components of these waxes were unbranched and branched C 16 -C 36 fatty acids and their esters, as well as alkanes, phytanols, phytanes and sterols.…”

Variability of water repellency in sandy forest soils under broadleaves and conifers in north-western Jutland/Denmark

“…the wetting and drying history of the soil (Doerr & Thomas 2000), temperature (Dekker et al 1998(Dekker et al , 2001, content and type of soil organic matter (Doerr et al 2005), thus by tree species respectively forest type . The infiltration capacity of water repellent soils can be distinctly lower than those of wettable soils (e.g.…”