13th International Conference on Integrated Diffuse Pollution Management (IWA DIPCON 2009). Lotte Hotel
World, Seoul, Republic of Korea : 12-15 October 2009
Effects of drying and rewetting on dissolved organic carbon (DOC) of two
alfisols in the north of Iran
1*
1
Amir Lakzian , Akram hallajnia and Hadiseh Rahmani
1
1
Department of Soil Science, Faculty of Agriculture, Ferdowsi University of Mashhad, Mashhad 91779, Iran
* Corresponding author. Tel: +98-511-8795612-7 (Ext. 294); fax: +98-511-8787430.
Email addresses lakzian@ferdowsi.um.ac.ir & alakzian@ yahoo.com
Abstracts
Drying and rewetting cycles affect many different
soil characteristics. Dissolved organic carbon is a very
important soil property, which can be affected by
drying and rewetting cycles. In the present study, the
effect of one to five drying and rewetting cycles was
investigated on two different soil samples collected
from north of Iran. The results showed that different
soil samples had different DOC concentration and it
was decreased by drying and rewetting cycles in both
soils.
Keywords: Alfisols, Dissolved Organic Carbon
(DOC), Drying and Rewetting.
Introduction
Drying and rewetting (DRW) are physical events that
occur commonly in the most agricultural land
especially in mediterranean-type climates (Buttery et
al 2008). The short and long-term effects of soil DRW
cycles on soil properties have not been well known.
Understanding the effects of DRW cycles on soil
chemical, physical and biological properties are
important because DRW affect aggregation processes
(Six et al 2000), humus decomposition (Birch 1958),
soil respiration (Franzluebbers et al 2000), changes in
microbial communities (Buttery et al 2008) and soil
nutrient cycling. Gordon et al (2007) showed that
DRW cycles leads to greater nutrient leaching from
improved than unimproved grassland soils, which
have a greater microbial biomass and abundance of
fungi relative to bacteria, in north Lancashire, UK.
Lundquist et al. (1999) suggested that increasing
DOC concentrations in two agricultural soils
subjected to drying and wetting may be partly
ascribed to the release of organic substrates from
plant roots. Fierer and Schimel (2001) reported that
DRW cycles induced significant changes in soil N
dynamics. Increasing N mineralization has been
referred to the exposure of easily decomposable
compounds originated from the death of microbial
organisms and fine roots and desorption of particle
surfaces (Bottner 1985; Denef et al. 2001; Van Gestel
et al. 1993). Alternatively, DRW cycles may cause
soil aggregates to break apart, exposing physically
protected organic matter (Lundquist et al 1999).
The aim of the present work was to investigate the
effects of multiple cycles of drying and rewetting
(slow-drying and fast rewetting) events on dissolved
organic carbon (DOC) and different forms of soil
nitrogen and phosphorus in two soils taken from
adjacent agricultural land in the north of Iran.
Materials and Methods
Soil sampling and experimental design
A microcosm pot experiment was set up in a
completely randomized design with three replications.
Soil samples were taken from 0-25 cm of soil surface
of two adjacent agricultural lands located at Lahyijan
37°11′N, 50°1’ ′W ( Soil 1) and 37°25′N, 49°25′W
(soil 2) in the north of Iran. Air-dried soil samples
sieved (< 2 mm), homogenized and stored at room
temperature for next use. Sub samples (60 g) of both
soils prepared for seven treatments (continuously dry
and wet, 1, 2, 3, 4 and 5 cycles of drying and
rewetting). Each cycle include three days drying (airdried) and two days wetting (at field capacity
moisture content). Figure 1 shows a schematic of the
experimental design.
FC level
23 days dry (1 cycle)
Air dry level
18 days dry (2 cycles)
13 days dry (3 cycles)
Sampling
Point
8 days dry (4 cycles)
3 day dry
(5 cycles)
Continuously wet
Continuously dry
Incubation Time (25 days)
Fig. 1. Sequence of treatments, water content during
DRW cycles and sampling time. Each dry/wet cycle
started by drying. Three days incubation dry and two
days incubation wet. Two soil samples considered as
control (continuously dry and wet)
Soil Extraction and analysis
Soil suspension (1:2.5 w/w) prepared and shacked for
240 minutes at 200 rpm. Soil suspensions were passed
through a filter paper (Whattman 42) and 0.45-µm
filter respectively. Dissolve organic C was determined
after filtration, acidification and purging (NPOC),
using a Shimadzu 5000A TOC-V CPH analyzer.
both examined soil. DOC strongly affected by the
amount of organic matter in soil samples.
b
200
180
Table 1 shows some chemical and physical
characteristics of two alfisols located in the north of
Iran, Lahyijan city.
DOC(mg/kg)
160
Results and Discussion
140
120
100
a
80
60
40
Table 1: Chemical and physical properties of two
examined soils
Conclusions
Drying and rewetting had a significant effect on the
concentration of dissolved organic carbon (DOC) in
a
250
b
b
d
e
e
e
5 cycles
a
4 cycles
a
3 cycles
200
150
c
c
c
4 cycles
b
100
3 cycles
c
50
1 cycle
2 cycles
Always wet
Always dry
0
5 cycles
The results of soil analysis showed that the amount of
organic carbon in soil 2 was 1.7 times higher than soil
1. In view of the fact that organic carbon is a very
important factor, it affects the dissolved organic
carbon of soils. Therefore, the amount of DOC
between two examined soils was remarkably
different. DOC content in soil 2 was 205mg/kg while
it was 87 mg /kg in soil 1 (Figure 1). It seems that the
difference between DOC in two tested soils was due
to the difference between the amount of organic
matter in soil samples.
The results also revealed that drying and rewetting
cycles treatments had a significant effect on DOC of
both soil samples. DOC concentration decreased by
increasing drying and rewetting cycles. Those
samples that permently were kept wet had the highest
amount of DOC. Then permanently dry treatments
had the highest amount of DOC compared to the
drying and rewetting treatments. The least amount of
DOC was observed when soil samples were treated by
5 cycles of drying and rewetting (Figure 2). The trend
of reduction in both soils was more or less similar.
DOC was reduced to 40 mg /kg in soil 1 while it
reached to 170 mg /kg in soil 2 after five cycles of
drying and rewetting treatments.
soil2
300
1 cycle
SL
24
5.1
0.63
31
0.64
5.23
8680
56
51.3
1.31
soil1
Figure1: The comparison of DOC in soil 1 and soil 2
2 cycles
%
dS.m-1
Cmol/kg
%
%
ppm
ppm
%
cm3/ g
Soil12
Always wet
Texture
Clay
pH
EC
CEC
CaCO3
OC
Total N
Inorganic N
SP
Bd
Soil1
1
CL
42
6
0.42
50
1.51
3.12
2520
168
50.8
1.28
Always dry
Unit
0
DOC (mg/kg)
Characteristics
20
Treatments
Figure2: Effects of drying and rewetting cycles on
DOC of soil 1 and soil 2 (Dark columns shows soil1
and white columns shows soil 2)
Acknowledgments
This research was financially supported by Ferdowsi
University of Mashhad,
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