沙漠研究 24-1, 81-84 (2014)
Ἃ₍◊✲ 24-1, 81 - 84 (2014)
Journal of Arid Land Studies
Journal of Arid Land Studies－ DT11 Refereed Paper －㸫DT11 Refereed Paper㸫

Evaluation of Salt Transport in the Amelioration of Salt-Affected Soil in China
by Using Low-Quality Coal Bio-Briquette AshYuji SAKAI*1), Hitomi SETO1) and Hidetoshi NAGAMOTO1)
Abstract: In countries with arid and semiarid regions, a decrease in agricultural production due to excessive salts in the soil is a very
serious problem. Recently, the need for development of new, clean coal-refining technologies has risen in China. In this study, weameliorated salt-affected soil by using coal bio-briquette ash, and the positive effects of this amelioration have been confirmed. Inaddition, we investigated the effect of salts leaching into coal bio-briquette ash by using a soil column equipped with tensiometers and4-electrode sensors. Ashes from 2 coal bio-briquettes made from low-quality coal (sulfur content = 2.1% and 4.1%), biomass (cornstem), and a desulfurizer (Ca(OH)2) were added to salt-affected soil. Consequently, initial sodium (Na) leaching was confirmed fromthe results of the leachate electroconductivity (EC) and Na content of the leachate at a 3.0wt% application rate. The effect of soil
amelioration by using coal bio-briquette ash originating from high-sulfur coal was more effective than that from low-sulfur coal. Our
research also indicates that ash has the capability of ameliorating high-EC and high exchangeable sodium percentage soils. Finally,
we predicted the necessary water volume for Na leaching in all fields by using the experimental results from the soil column and themeteorological data from all cities. Consequently, we could estimate the quantity of irrigation water necessary in all cities. Theseresults indicated the effectiveness of using low-quality coal bio-briquette ash as an amendment to salt-affected soil, and its use inpredicting the reclamation time and necessary volume of water for soil amelioration.
Key Words: Coal bio-briquette, Hydraulic conductivity, Salt-affected soil, Salt transport, Soil amelioration

1. Introduction
Salt-affected soils occur in more than 100 countries
worldwide, with variations in the extent of affected soil andnature and properties of the soil (Rengasamy, 2006). The
decrease in agricultural production due to excessive salts in thesoil is a very serious problem, because insoluble salts that haveaccumulated in the soil obstruct the growth of vegetation
because of the osmotic pressure that they exert. Moreover,
the accumulation of monovalent cations (mainly sodium, Na+)
causes deterioration of the soil’s physical properties from thedispersion and swelling of clay, which makes it difficult forplants to grow. These processes adversely affect water
penetration, infiltration speed, and moisture transport
properties of the soil.
Therefore, leaching unwanted
chemicals from the soil by using large amounts of water isrequired to improve such salt-affected soils.
The use of chemical amendments is an effective method toreclaim salt-affected soils. Amelioration of salt-affected soil
involves the replacement of exchangeable Na with calcium(Ca) supplied by the presence or addition of gypsum, soil lime,
or both (Oster and Frenkel, 1980). Reclamation can beachieved by leaching with chemical amendments added to the* Corresponding Author: sakai@cc.kogakuin.ac.jp2665-1 Nakano-machi, Hachioji-shi, Tokyo 192-0015, Japan1) Department of Environmental and Energy Chemistry, Kogakuin University, Japansoil or irrigation water (Keren and Miyamoto, 1990). Soilsalinity can be directly measured using buried porous electricalconductivity (EC) sensors, 4-electrode probe systems,
electromagnetic induction sensors, or time domainreflectometry systems (Rhoades and Oster, 1986; Rhoades,1992). In particular, a 4-electrode probe has been shown assuitable for observing the salt concentration in a column withwater flow (Inoue et al., 2000).
On the other hand, in China, air pollution is also a serious
environmental problem. Recently, desulfurization equipment
was installed at large facilities such as coal-fired power plants.
However, low-quality coal containing high percentages ofsulfur and ash are used for cooking and heating in rural
households in China; therefore, indoor pollution from coal
combustion in rural areas is a critical problem, and there aremany concerns about damage to health. Hence, we used coalbio-briquettes that also have merits because of theirdesulfurization ability and can be made using low-quality coaland biomass in China. Moreover, Sakai et al. used thecombustion ash of coal bio-briquettes as salt-affected soil
amendments in China and effective reclamation results havebeen confirmed (Sakai et al., 2011).
In this study, our objective was to investigate the effect ofNa leaching and the water volume necessary for Na leaching㸦Received, September 14th, 2013; Accepted, February 10th, 2014㸧

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Table 1. Soil chemical properties, hydraulic conductivity (KW), andsoil texture of 4 tested soils.
pH [-]
Soil 1
Soil 210.5
10.1

Soil 39.3

EC[dS m-1]
0.8

ESP*[%]
25.0

0.6
2.1

20.4
35.0

K w**[cms-1]
6.6 × 10-8
1.9 × 10-6
2.6 × 10-6

ST ***SCLLSSCL*ESP: exchangeable sodium percentage, **Kw: Saturated hydraulicconductivity, ***ST: Soil Texture
Table 2. Chemical properties of soil amendments.
BB 1*
BB 2**CaSO4

CaSO4 + Ca(OH)2***

pH[-]
8.5
10.9
7.4
12.7

EC [dS m-1]
2.3
2.4
2.1
8.9

ex. Ca**** [mmoldm-3]
14.7
27.4
152277*BB 1: Combustion ash from coal bio-briquette (S content in coal = 2.1%)**BB 2: Combustion ash from coal bio-briquette (S content in coal =4.1%), ***: CaSO4:Ca(OH)2 = 1:1 (weight ratio), ****ex. Ca:
exchangeable calcium concentrationby using coal bio-briquette ash made from low-quality coal as
an amendment for salt-affected soil. In addition, we predicted
the necessary volume of irrigation water for field tests fromboth the experimental results and meteorological data fromeach test site.

2. Materials and Methods
2.1. Soil properties and soil amendments
Three soils (Soil 1, Soil 2, and Soil 3) were used for thecolumn infiltration experiment. Soil 1, Soil 2 and Soil 3 weresampled in Shenyang, Datong and Yinchuan, China,respectively. Chemical properties such as soil pH, EC, andexchangeable sodium percentage (ESP) are provided in Table
1. All soils are characterized by a high pH and high ESP. In
particular, EC and ESP in Soil 3 were higher than that in othersoils. Saturated hydraulic conductivity (KW) of Soil 1 waslower than that in other soils. Two types of ash from coalbio-briquettes made with low-quality coal with sulfur (S)contents of 2.1% and 4.1% were used for soil amendment.
Ashes were labeled BB 1 (S = 2.1%) and BB 2 (S = 4.1%).
For reference, the CaSO4 and CaSO4 + Ca(OH)2 (weight ratio= 1:1) properties are provided in Table 2. The pH, EC andion concentration of a 50-mL solution mixed with 10 g soil
were measured using a pH meter and an EC meter (F-55,Horiba) and an ICP-AES (SPS3500UV, SII), respectively.
The chemical properties of the soil amendments weremeasured in solution (soil: water = 1:10 (weight ratio)). The
pH in BB 2 and CaSO4 + Ca(OH)2 was higher than that in BB
1 and CaSO4. EC in CaSO4 + Ca(OH)2 was the highest in all
soil amendments. The concentration of exchangeablecalcium (Ca) in BB ash was lower than that in Ca compounds.

Fig. 1. Schematic illustration of the experimental column setup.

2.2. Column Infiltration Test
Soil samples < 2 mm were mixed uniformly with BB ashes
at application rates of 3.0 wt% at a bulk density of 1.53 g cm-3.
An acrylic ring with an outer diameter of 60 mm, innerdiameter of 50 mm, and height of 20 mm was filled to 20 cm.
Degassed water was poured onto the top of the column at a rateof 1.0 × 10-3 – 2.0 × 10-3 cm3 s-1 by using a peristaltic pump.
Tensiometers and 4-electrode sensors (Inoue et al., 2000) wereinserted into the column at depths of 5, 9, 13 and 17 cm, and at
5 and 17 cm (where soil surface z = 0 cm), respectively. In
our research, we used a 4-electrode sensor as an indicator of
total salt concentration in the soil column to observe the runoff
rate of salts. Tensiometers were equipped with a transducer
to measure the pressure (cmH2O) of the soil in theexperimental column. Transducers (TD 1 [z = 5 cm], TD 2 [z= 9 cm], TD 3 [z = 13 cm] and TD 4 [z = 17 cm]) connected to
4 tensiometers and two 4-electrode sensors (FES; FES 1 [z = 5cm] and FES 2 [z = 17 cm]), were connected to a data logger(CR10X, Campbell Scientific, Inc.) using a PC (Fig. 1). The
measurements were controlled in the program by using theapplication software (PC208W, Campbell Scientific, Inc.).
Moreover, to examine the soil solution that seeped from thelower part of the experimental column, we collected theinfiltration solution at constant time intervals using a fraction
collector. The water volume was measured at each timeinterval. The ion concentrations (Na+, Ca2+, magnesium(Mg2+), potassium (K+) and chlorine (Cl-)) in the effluent
solution were quantified using ICP-AES. The soil pH andEC of each solution were also measured. These experiments
were performed at 25°C.

3. Results and Discussion
We examined the effect of Na leaching using BB 1 and BB
2 in Soil 2. The effect of Na and electrolyte concentrations inrelation to Kc and infiltration were discussed. Swelling and83

Fig. 2. Change in Na concentration of leachate at the application rateof 3.0 wt% (BB 1, BB 2).

Fig. 4. Change in hydraulic conductivity (Kc) in the soil column at
the application rate of 3.0 wt% (BB 1, BB 2).

Fig. 3. Change in electrical conductivity (EC) of leachate at theapplication rate of 3.0 wt% (BB 1 and BB 2).

Fig. 5. Change in sodium (Na) concentration of leachate at 3.0 wt%
application rate of BB 2 (Soils 1, 2 and 3).

dispersion are the primary processes responsible fordegradation of the physical properties of soil in the presence of
Na. The Na concentration in effluent after infiltration into thecolumn decreased by about 1 PV (pore volume) (Fig. 2). The
behavior of leachate EC in the BB 1 and BB 2 applications
was similar to Na concentration in BB 1 and BB 2,respectively (Fig. 3). The necessary water volume under 4
dS m-1 was 0.77 PV (0.116 dm3) in BB 1 and 0.78 PV (0.107dm3) in BB 2 (Fig. 3).
In a previous study in Soil 1, that was 0.90 PV (0.142 dm3)
in 0.5 wt% application rate of CaSO4 (Sakai et al., 2009).
This result indicates that the necessary water volume for soil
amelioration in coal bio-briquette ash is smaller than that ingypsum. The Kc in the soil column after 1 PV in BB 1 andBB 2 was approximately 10-4 cm s-1 and 10-6 cm s-1,respectively (Fig. 4). The difference between the 2 hydraulicconductivities is a result of the difference of exchangeable Caconcentration (Table 2).
Next, BB 2 was added to Soil 1, Soil 2 and Soil 3 at theapplication rate of 3.0 wt%. Na concentration and EC in theleachate of all soils increased at the beginning of the leachingprocess and then drastically decreased (Figs. 5 and 6). Most

Fig. 6. Change in electrical conductivity (EC) of leachate at 3.0 wt%
application rate of BB 2 (Soils 1, 2 and 3).

of the salts, mainly Na, were leached in 1 PV; therefore, thewater volume for salt leaching in soil was nearly the same, andthe total time for soil reclamation depended on the water
penetration speed. The order of Kc in the soil column wasalmost the same as that in the original soil (Fig. 7 and Table 1).
This addition of divalent cations to the soil solution can reduceclay dispersion and increase Kc in the soil profile (Keren andMiyamoto, 1990); therefore, Ca ion originating from coalbio-briquette ash was effective for reclamation of Kc in soil.

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low-quality, high-sulfur coal was effective for Na leaching insalt-affected soil amelioration.
Coal bio-briquette ashcontaining a large amount of exchangeable Ca is highly
capable of Kc reclamation and salt leaching. By using thecolumn infiltration test, the necessary water volume for saltleaching was found to be nearly constant and the period ofreclamation depended on the Kc. Thus, by using oursimulation model, the necessary irrigation water volume could
be calculated.

Fig. 7. Change in hydraulic conductivity (Kc) in the soil column at
3.0 wt% application rate of BB 2 (Soils 1, 2 and 3).
Table 3. Simulated necessary irrigation water volume in all sites in China.
Water quantity for Naleaching in column
3experiment (Q) [dm3]Soil 1
Soil 2
Soil 30.24980.23840.3479Quantity of infiltration
3

water to soil (I) [dm ]0.13340.20160.1027

Necessary irrigationwater volume (Q-I)[dm3]
0.11640.03680.2452

We predicted the completion time for salt leaching in thetest field by using the results obtained from the column
experiment, water balance equation, evapotranspiration
equations, and meteorological data (Sakai et al., 2009). In
this study, the effect of coal bio-briquette ash was comparedwith that of desulfurization gypsum (Sakai et al., 2009). This
simulation method is the same concept; however, both averagetemperature and precipitation during the corn-growing season(from April to October) in 3 cities was introduced to thewater-balance equation, and the quantity of irrigation water andtotal shortwave radiation was assumed to be the same value inthe 3 cities. Consequently, the necessary water quantities for
Na leaching in the soil column experiment (Q) were 0.2498
dm3 in Soil 1, 0.2384 dm3 in Soil 2 and 0.3479 dm3 in Soil 3(Table 3).
Considering the average temperature andprecipitation in each city, the quantity of infiltration water tosoil (I) was 0.1334 dm3 in Soil 1, 0.2016 dm3 in Soil 2 and0.1027 dm3 in Soil 3 (Table 3); therefore, their water quantity
was insufficient for leaching nearly all Na in the soil. Since
the average irrigation water quantity in China is approximately
0.1472 dm3 (Tian et al., 2003), the necessary irrigation water
volume for Soil 1 and Soil 2 was within this average volume;
however, in Soil 3, the irrigation water volume had to be
increased.

4. Conclusion
Combustion ashes from coal bio-briquette made using

Acknowledgement
We express our appreciation to Prof. Changhe Chen(Tsinghua University) and Prof. Chang Wang (Tianjin
University of Science & Technology) for their assistance in thisexperiment and investigation. This study was supported by
the Kurita Water and Environment Foundation (KWEF).

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