WATER REPELLENCY OF POST-BOGGY SOILS WITH A VARIOUS CONTENT OF ORGANIC
MATTER
Andrzej Lachacz, Monika Nitkiewicz & Barbara Kalisz
Department of Soil Science and Soil Protection, University of Warmia and Mazury in Olsztyn,
Pl. Łódzki 3; 10-957 Olsztyn, Poland, phone: +4889-5233879, e-mail: andrzej.lachacz@uwm.edu.pl
The objective of this study was to estimate the water repellency of post-boggy soils in north-eastern
Poland. A total of 276 soil samples with a varied organic carbon (OC) content, ranging from trace
amounts in sandy subsoils to 44.4% in organic soils, were analyzed. The investigated material
represents peat-muck soils (Eutri-Sapric Histosols) and muck-like soils (Arenic Gleysols, Areni-Humic
Gleysols, Gleyic Arenosols). The mineral matter of the analyzed soils comprised loose sand. Soil
samples were divided into groups based on their organic matter content and depth in soil profile.
Surface layers containing more than 12% OC (> 20% LOI) were described as muck soil formations,
while surface layers with 1.3-12% OC content – as muck-like soil formations (humose sands). Organic
soil formations in soil profiles deeper than 20 cm comprise lowland alder peat, usually under muckforming process, and strongly decomposed alder peat in deeper layers. Another group of investigated
samples consisted of mineral soil formations (<1.3% OC) underlying muck soils and muck-like soils.
Soil samples collected at a depth of 0-20 cm were described as surface formations, while samples
obtained from deeper layers (20-100 cm) – as subsurface formations. Samples were air-dried, visible
plant remnants were removed by hand picking and the material was passed through a 2.0 mm mesh
sieve. Potential water repellency was determined based on the water drop penetration time (WDPT)
test and the alcohol percentage (AP) test (Doerr 1998).
The majority (60.9%) of the 276 investigated soil samples were hydrophilic, with water drop
penetration time below 5 seconds. Based on the above results, the samples were classified into the
first water repellency category (Table 1). The remaining samples showed different degrees of water
repellency.
Table 1. Hydrophobicity categories of investigated groups of soil formations
WDPT determination
Cat.
1
2
3
4
5
6
7
8
9
10
Time
(s)
<5
5-10
10-30
30-60
60-180
180-300
300-600
600-900
900-3600
3600-18000
Σ
All
samples
studied
n
168
20
17
9
10
9
5
5
10
23
276
%
60.9
7.2
6.2
3.3
3.6
3.3
1.8
1.8
3.6
8.3
100.0
>12% Corg
Depth
0-20 cm
n
%
12
21.8
0
0.0
6
10.9
3
5.5
5
9.1
7
12.7
2
3.6
3
5.5
7
12.7
10
18.2
55
100.0
20-100 cm
n
%
0
0.0
0
0.0
2
10.0
0
0.0
0
0.0
0
0.0
1
5.0
2
10.0
3
15.0
12
60.0
20
100.0
1.3-12% Corg
Depth
0-20 cm
n
%
92
74.8
15
12.2
6
4.9
4
3.3
3
2.4
2
1.6
1
0.8
0
0.0
0
0.0
0
0.0
123
100.0
20-100 cm
n
%
38
77.6
4
8.2
1
2.0
2
4.1
2
4.1
0
0.0
1
2.0
0
0.0
0
0.0
1
2.0
49
100.0
0-1.3% Corg
Depth
0-100 cm
n
%
26
89.7
1
3.4
2
6.9
0
0.0
0
0.0
0
0.0
0
0.0
0
0.0
0
0.0
0
0.0
29
100.0
The obtained results indicate that peat soil formations are marked by higher potential water repellency
than muck soil formations. The highest WDPT values (16 390 s) were reported in respect of an alder
peat sample with 41.9% OC content, collected at a depth of 55-60 cm. In the group of muck soil
formations, a sample with 36.7% OC content, collected at a depth of 15-20 cm, was marked by the
highest water repellency (WDPT 10 492 s). It can be concluded that the potential water repellency of
organic soil formations is not determined by the depth of their deposition in the soil profile.
Humus-rich surface soil formations with OC content of 1.3% to 12% were mostly hydrophilic, and
74.8% of samples were classified into category 1. Similar results were noted in respect of subsurface
formations with an identical OC content. Mineral formations containing less than 1.3% OC proved to
be hydrophilic and 89.7% of the samples were classified into category 1. This group of formations did
not contain samples with water drop penetration time longer than 30 seconds. None of all investigated
samples (n = 276) was characterized by water drop penetration time longer than 18 000 seconds (>5
hours), which permits their classification into the highest water repellency category (11) according to
Doerr (1998).
2
The water repellency of the studied soils is determined by their organic matter content and it is clearly
manifested only when organic matter content exceeds 20% (Fig. 1A). For this reason, the dependency
between WDPT and LOI is curvilinear.
A
B
18000,0
30
16000,0
y = 72.986x - 690.16
R2 = 0.605
n=55
20
AP (%)
12000,0
WDPT (s)
y = 0.6523x - 8.46
25
R2 = 0.504
n=276
14000,0
10000,0
8000,0
6000,0
15
10
4000,0
5
2000,0
0,0
0
0,0
10,0
20,0
30,0
40,0
50,0
60,0
70,0
80,0
90,0
100,0
0,00
5,00
10,00
15,00
Loss-on-ignition (%)
20,00
25,00
30,00
35,00
40,00
45,00
OC (%)
C
D
18000,0
8
y = -6220.7x + 46265
16000,0
14000,0
y = 0.5346x + 0.60
7
2
R = 0.564
2
R = 0.9178
n=20
n=276
6
5
10000,0
AP-cl.
WDPT (s)
12000,0
8000,0
4
3
6000,0
2
4000,0
1
2000,0
0,0
0
0,0
1,0
2,0
3,0
4,0
5,0
pH (H2O)
6,0
7,0
8,0
9,0
0
2
4
6
8
10
12
WDPT cat.
Fig. 1. Relationship between potential water repellency and some soil properties
Organic formations (>12% OC) are characterized by varied degrees of water repellency, but WDPT
values in excess of 2 000 s are demonstrated only by formations with OC content higher than 35%. In
the entire studied population (n = 276) a significant positive correlation was determined between the
content of organic matter, organic carbon, total nitrogen and all water repellency parameters. It should
be noted that the coefficients of correlation are higher for water repellency expressed as AP (%) than
for WDPT expressed as an arithmetic mean or median. In this group of soil formations, a significant
positive correlation was also stated between WDPT and the C:N ratio, while a significant negative
correlation was reported in respect of pH(H2O). A relatively strong correlation between the degree of
water repellency and organic matter content was also noted by other authors (e.g. Buczko et al. 2005).
There was a strong negative correlation between water repellency and pH for surface and subsurface
organic formations (Fig. 1C). The results of the WDPT test, expressed as the hydrophobicity category,
and of the AP test, expressed as the hydrophobicity class, were strongly correlated (Fig. 1D). It should
be noted, however, that AP of class 5 corresponds to as many as 7 WDPT categories. The above is
consistent with the findings of Doerr (1998).
Key words: hydrophobicity, potential water repellency, WDPT-test, soil organic matter, post-boggy
soils, sandy soils
References
Buczko U., Bens O. & Hüttl R.F. 2005. Variability of soil water repellency in sandy forest soils with
different stand structure under Scots pine (Pinus sylvestris) and beech (Fagus sylvatica). Geoderma
126(3-4): 317-336.
Doerr S.H. 1998. On standardizing the ‘Water Drop Penetration Time’ and the ‘Molarity of an Ethanol
Droplet’ techniques to classify soil hydrophobicity: a case study using medium textured soils. Earth
Surf. Process. Landforms 23: 663-668.