IJERD – International Journal of Environmental and Rural Development (2012) 3-1

Research article
erd

Effects of Burning Crop Residues on Soil Quality inWenshui, Shanxi of China
LIEXIANG LI
Graduate School of Agriculture, Tokyo University of Agriculture, Tokyo, Japan
Email: liexiang_1@163.com

YUTA ISHIKAWA
Graduate School of Agriculture, Tokyo University of Agriculture, Tokyo, Japan

MACHITO MIHARA*
Faculty of Regional Environment Science, Tokyo University of Agriculture, Tokyo, Japan
Email: m-mihara@nodai.ac.jp
Received 16 December 2011

Accepted 7 February 2012(*: Corresponding Author)

Abstract Large amount of crop residues are produced every year in China. Although cropresidues are rich in organic matter, nitrogen, phosphorus, potassium, calcium andmagnesium, local farmers tend to burn residues in the fields in order to simplify
preparation for following cultivations and to enhance the development of economicconditions. Thus, attention has been paid to the effects of crop residues burning on soilenvironment. The objectives of this study are to observe changes in burning density and toevaluate changes in soil quality caused by burning practices in Wenshui, Shanxi of China.
Burning density was analyzed based on the Fire Information for Resource Management
System (FIRMS). In addition, onsite experiment on residue burning was conducted inWenshui and soil samples were collected for evaluating the change of soil quality and soil
fauna. It was observed that the burning density in Wenshui of Shanxi in 2009 was muchlarger at 0.0467 events/km2/year than that in 2001 at 0.00141 events/km2/year. Also, theresults of onsite experiment on residue burning conducted in Wenshui indicated that soil
surface temperature rose to 415 degrees Celsius resulting in the sudden decrease ofmicroorganism population. In addition, values of electrical conductivity (EC) and pH
increased to 219 mS/m and 9.04, respectively. However, there was a slight decrease in soil
permeability. Burning crop residues on farmland may accelerate nitrogen loss. Besides,
concentration of phosphorous in soil tended to increase with the burning process.
Therefore, it was concluded that the burning of residues significantly affects soil
ecosystem and its quality.
Keywords burning crop residues, soil quality, microorganism

INTRODUCTIONIn China, the yield of crop residues is 79,454.4×104 tons per year and increases steadily at a rate of
1,251.2×104 tons every year (Zhong et al., 2003). Crop residues were important sources of energy
in many parts of China, where crop residues were mainly utilized as domestic fuel. However, cropresidues utilized as domestic fuel has been disregarded due to the adaptation of other fuel sources(Yan et al., 2005). This situation causes a significant increase of crop residues in fields as Song etal. (1995) breported that crop residues used as domestic fuel decreased about 50%. Therefore, local
farmers tended to burn residues in the field in order to simplify the preparation for the following
cultivation. Although there were many reports on the effects of crop residue burning on soil quality,
few studies have been conducted in China, especially in Shanxi. Therefore, this study has beenproposed. The objectives of this study are to observe changes in burning density and to evaluatechanges in soil quality caused by burning practices in Wenshui, Shanxi of China. On the other hand,Srimuang et al. (2004) reported that the burning process affects soil physical and chemicalⒸ ISERD

30IJERD – International Journal of Environmental and Rural Development (2012) 3-1properties up to 15 cm deep from soil surface. In addition, high soil temperatures may kill soil
microbes and plant roots, destroy soil organic matter, and degrade soil nutrients as well as water
holding capacity (Srimuang, 2006).
METHODOLOGY
The research site is located in Xiaqu Village, Wenshui of Shanxi Province, in the central part ofChina (37˚26’N, 112˚01’E, 767 m above sea level). The region has a continental monsoon climate
and is rather arid having an average annual precipitation around 350-700 mm. Upland field farmingis the main agricultural activity in Shanxi Province. The total area in Wenshui is 1,064 km2 inwhich upland field occupies about 400 km2 or about 40% of the total area. The dominant soil typein the study is SL as shown in Table 1.
Table 1 Soil texture of Wenshui, Shanxi, China

Depth (cm)0-20Specificgravity
2.77

Particle size distribution (%)
Gravel Coarse sand Fine sand00.3866.54

Silt
23.80

Soil texture
Clay9.28

SLThe burning density was analyzed based on the Fire Information for Resource Management
System (FIRMS). FIRMS integrates remote sensing and GIS technologies to deliver global MODIS
hotspot/fire locations and burned area information to natural resource managers and otherstakeholders around the world (Web Fire Mapper, 2010). The area monitored was comprised in a30 km radius from the center of Wenshui, Shanxi of China. Data were gathered in a yearly basis
from 2001 to 2009.

20012009

Fig. 1 Changes in burning density around Shanxi of China
For the field burning experiment, an observation pit of 1 m wide, 1 m long and 1 m deep wasexcavated in the corn field, near a burned pile of crop residues for observing soil temperature andvolumetric water content. Dried corn residues were burned within 30 minutes right beside the pit asshown in Fig. 2-a. Soil temperature and moisture were measured by using a thermocouple and awater content reflect meter inserted into the wall of the pit (Fig. 2-b) at different depths of 1, 5, 10,20, 30 and 40 cm from soil surface. Measurements were done at 5, 10, 30, 60, 120, 180, 240, 300,320, 360 and 420 minutes passed after burning.
For laboratory analysis, two different types of soil were collected from field site: unburnedsoil and burned soil. Both soils were collected from the same field. However, burned soil wascollected from a burning experimental plot. To observe the effects of burning on general
microorganisms, some amounts of unburned soils were burned by oven at 415 degrees CelsiusⒸ ISERD31

IJERD – International Journal of Environmental and Rural Development (2012) 3-11mwithin 30 minutes to correspond to the condition of soil during the burning at the field site. Forburned soil as well as unburned soil, analysis of general microorganisms was carried out with anagar plate.

1m(a)

(b)

(c)

(d)
Fig. 2 Field burning experiment conducted in Wenshui Shanxi of China

In addition, saturated permeability test was conducted by falling head method. Both unburnedand burned soils were undergone for soil general bacteria, electrical conductivity (EC) and pH, tomake out the effects of residue burning on soil chemical and physical properties. Also, changes intotal nitrogen and total phosphorous in soil were analyzed under different temperatures.
RESULTS AND DISCUSSION
Burning density was analyzed on the basis of the Fire Information for Resource Management
System (FIRMS). Results from the analysis on changes in burning density showed that burning
density in Wenshui of Shanxi in 2009 at 0.0467 events/km2/year was much larger than that in 2001
at 0.00141 events/km2/year. It was observed that burning density in 2009 was 33 times higher thanthat in 2001 as shown in Fig. 3.
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Burning density (number/km2/year)

0.05
y = 0.0048x - 9.5078
R = 0.8061

0.04
0.03
0.02
0.01
02001

2003

2005

2007

2009

Time (year)

Fig. 3 Burning density occurred from the year 2001 to 2009
On site burning was conducted to measure soil volumetric water content (VWC) and soil
temperature in a corn field located at Wenshui, Shanxi of China. Experimental results indicated thattemperature of surface soil rose to 415 degrees Celsius (Fig. 4) immediately after starting theburning, and then it decreased gradually with time after ceasing the burning. Also, it was observedthat soil volumetric water content at depths of 1 cm to 40 cm decreased with burning. However,this decreasing tendency of soil volumetric water content at 1 cm deep lasted until the end of theobservation. In addition, at other depths, there was some fluctuation of soil volumetric watercontent as shown in Fig. 5.
For evaluating changes in soil quality with the burning, values of EC and pH were analyzed.
The changes in EC and pH values were measured by glass electrode method. The values of pH
increased from 8.23 to 9.04 with the burning and there was a significant difference between pH
values of unburned and burned soils at 99% confidence interval (Fig. 6). Also, values of electricalconductivity (EC) increased to 219 mS/m from 128 mS/m with the burning (Fig. 7).
surface
soil
1cm

400

5cm
10cm

300

20cm
30cm

200

40cm

10000100200
300
Time（minute)20
Volumetric water content (%)

Temperature （℃）

500

5cm
10cm

1220cm

830cm
40cm

400100

200

300

400

Time（minute)

B**

Fig. 5 Changes in VWC with burning
B**250A**200EC (mS/m)

86pH

16400

Fig. 4 Changes in temperature with burning

101cm42A**
150
100
500Unburned soil

0Burned soil

Unburned soil

Fig. 6 Changes in pH with burning

Burned soil

Fig. 7 Changes in EC with burningⒸ ISERD

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IJERD – International Journal of Environmental and Rural Development (2012) 3-1

The population of general microorganisms in unburned and burned soils was measured
employing an agar plate. Results indicated that general microorganisms existing in unburned soil
were 3.0×107 cfu/g while there was no general bacteria found in the burned soil (Fig. 8). Results
indicated that general bacteria cannot live at 415 degrees Celsius that was observed in the fieldburning experiment in Wenshui, Shanxi of China. Thus, the effect on the destruction of soil
microorganisms is a big concern for soil environment researchers.
However, no significant change was observed in permeability between unburned and burnedsoils. Also, a significant difference was not observed as shown in Fig. 9.
0.0040Coefficient of permeability (cm/s)

A**

General bacteria (cfu/g)

3.00E+07
3×107

2.00E+07
2×107

1×107
1.00E+07

B**

0.0030AA0.0020

unburned soil

0.0010burned soil

0.000000.00E+00
Unburned soil

0Burned soil

10203040

50

60

Amount of flow (ml)Fig. 8 Changes in general bacteria with burning

Fig. 9 Changes in water permeabilitywith burning

The changes in total nitrogen and total phosphorous concentration with the burning are shownin Fig. 10 and Fig. 11. A tendency for total nitrogen to decrease with the burning temperature wasobserved. This tendency may be caused by the release of nitrogen components into the air with theburning (Fig.10). However, total phosphorous tended to increase with the burning temperature dueto the decomposition of phosphorus component in soil.

14

unburned soil

12burned soil

108y = -0.0463x + 19.6
R = 0.8772

64
200

100

200

300

400

unburned soil

34
Total phosphorous (10-5 kg/kg)

Total nitrogen (10-5 kg/kg)

16500

burned soil

32
30
28
26

y = 0.0162x + 22.953
R = 0.92422200Temperature (℃）

100200300

400500Temperature (℃)

Fig. 10 Changes in total nitrogen with burning Fig. 11 Changes in total phosphorouswith burning
CONCLUSION
The results from the observation of changes in burning density showed that burning density in
Wenshui of Shanxi in 2009 at 0.0467 event/km2/year was much larger than that in 2001 at 0.00141
event/km2/year. Also, the results of onsite experiment on residue burning conducted in Wenshui
indicated that when soil surface temperature rose to 415 degrees Celsius, it caused the decrease ofmicroorganism population. Therefore, burning of crop residues significantly affects the micro
fauna in the soil. In addition, burning of crop residues also influenced the acidity of soil asⒸ ISERD34IJERD – International Journal of Environmental and Rural Development (2012) 3-1

indicated by the increase of soil electrical conductivity (EC) and pH. Moreover, a significant
decrease of total nitrogen component in the soil was observed. However, burning of crop residue
has no significant effect on soil permeability as observed in the permeability test.
It was concluded that the burning of crop residues influenced the degradation of soil
ecosystem and its quality. Therefore, treating of crop residues such as composting, for bio-fertilizer
on crop is strongly recommended.
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China Biogas, 23 (2), 11-14.
Song, J. 1995. The investigation and research on the straw resources in Zhejiang province. Soil andFertilizers, (2), 23-26.
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Han, L. and Yan, Q. 2002. Straw resources and their utilization in China. Transactions of the Chinese Societyof Agriculture Engineering, 18 (3), 87-91.

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