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Wind erosion and sand accumulation effects on soil properties in Horqin Sandy Farmland, Inner Mongolia
Catena 65 (2006) 71 – 79 www.elsevier.com/locate/catena
Wind erosion and sand accumulation effects on soil properties in Horqin Sandy Farmland, Inner Mongolia Ha-Lin Zhao a, Xiao-Yong Yi a, Rui-Lian Zhou a, Xue-Yong Zhao a, Tong-Hui Zhang a, Sam Drake b,* a
Cold and Arid Regions Environment and Engineering Institute, Chinese Academy of Sciences, 260 Donggang West Road, 730000, Lanzhou, P.R. China b Office of Arid Lands Studies, University of Arizona, 1955 E. 6th Street, Tucson, AZ 85719, USA Received 9 March 2004; received in revised form 14 September 2005; accepted 3 October 2005
Abstract Rain-fed agriculture is widespread in Inner Mongolia, northern China, where wind erosion of farmland is very common because of sandy soil and dry, windy weather. However, very little is known about the effects of wind erosion on soil physical and chemical properties in this region. A field experiment was conducted in sandy farmland, where erosional and depositional gradients were established to evaluate the effects of wind erosion and leeward sand accumulation on soil texture, nutrient content, soil water, and soil temperature. The research showed that long term wind erosion could result in significant soil coarseness, infertility and dryness. Severe erosion reduced clay by 59.6%, organic C by 71.2%, total N by 67.4%, total P by 31.4%, available N by 64.5%, available P by 38.8%, and average soil water content by 51.8%, compared with non-eroded farmland in the study region. The sand fraction (particles > 0.05 mm), pH and ground-surface temperature increased by 6.2%, 3.7%, and 2.2 -C, respectively. Accumulated sand also caused a decrease in nutrients and soil water content. Under severe sand accumulation, clay was reduced by 2.0%, organic C by 19.3%, total N by 21.7%, total P by 13.7%, available N by 52.5%, and average soil water content by 26.6%. The sand fraction, pH, available P, and ground-surface temperature increased by 0.2%, 0.9%, 5.8% and 2.8 -C, respectively. D 2005 Elsevier B.V. All rights reserved. Keywords: Wind erosion; Particle size distribution; Soil nutrients; Soil moisture; Sandy farmland; Inner Mongolia
1. Introduction Wind erosion not only results in destruction of soil structure, but also affects land production potential (Lopez, 1998). Thus wind erosion is considered to be a principal mechanism of land degradation (Hennessy and Kies, 1986; Okin et al., 2001) and is one of the most serious environmental and agricultural problems in many arid and semiarid agricultural regions of the world (Gomes et al., 2003). Although it is not a new phenomenon, wind erosion is currently recognized as a major source of environmental degradation. Areas of wind erosion have increased, and current knowledge of its environmental and economic impacts suggests that appropriate measures need to be taken for soil protection (Pimentel et al., 1995; Saxton, 1995). * Corresponding author. Tel.: +1 520 621 4501; fax: +1 520 621 3816. E-mail address: [email protected] (S. Drake). 0341-8162/$ - see front matter D 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.catena.2005.10.001
Research on wind erosion has increased in recent years (Gomes et al., 2003). Farmland soils are vulnerable to erosion by wind in arid and semiarid regions because such soils are relatively coarse-grained and generally lack crop coverage in the windy season (Su and Zhao, 2003; Li et al., 2004). Therefore, there is a need for additional studies of the characteristics and management of this kind of farmland (Ba¨rring et al., 2003; Larney et al., 1998). Over the last 50 years in China, about 9.1 107 ha of farmland have been damaged by wind erosion each year, and 6.7 106 ha of farmland have been buried by mobile dunes, mostly in the sandy rain-fed agricultural regions of Inner Mongolia, northern China (Wang, 2000; Zhao et al., 2003). To understand the effects of wind erosion on the ecoenvironment, researchers have investigated the mechanisms of erosion on different types of farmland and the spatial distribution of eroded farmland in this area (Zhu and Chen, 1994; Wang, 2000), the characteristics of soil degradation
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caused by wind erosion (Su et al., 2002; Su and Zhao, 2003), and the effects of wind-blown sand on crop growth (Xu and Liou, 1997; Li et al., 2004). However, some effects of wind erosion are still not well known, particularly the effect of accumulated sand on the agricultural soil environment in semi-arid areas of China (Zhao et al., 2003). Thus, the objectives of this study were to analyze changes in the physical and chemical properties of agricultural soils due to long-term wind erosion and leeward sand accumulation, and to evaluate the relationships among different soil properties and soil degradation processes.
2. Materials and methods 2.1. Study area The study area is located in the Horqin sand land (42- 55V N, 120- 42VE, 345 m above sea level) in the eastern part of Inner Mongolia, which belongs to the continental semi-arid monsoon climate in the temperate zone. Mean annual precipitation is 366 mm, mean annual potential evaporation is 1935 mm, and the mean annual temperature is 6.8 - C. The annual frost-free period is about 130– 150 days. The average annual wind speed is 3.4 m s 1 and mean wind speed in the wind erosion season (spring) is 4.3 m s 1. The landscape in this region is characterized by different types of dunes alternating with gently undulating lowland areas. The thickness of the soil layer in the farmlands is about 30 – 45 cm and the soil consists mainly of coarse sand and silt; the C Horizon is sand aggraded during the Quaternary period. Corn (Zea mays L.) monoculture dominates the cultivated land. In this system, the corn is planted at the end of April and harvested at the end of September, leaving the soil bare for about 7 months, from October through April of the following year. Wind erosion is very pronounced during the spring season. From the thawing of the frozen surface in mid-March until the sowing of crops at the end of April, the loose soil surface is dry and bare, and thus extremely susceptible to wind erosion (Li et al., 2004).
operated by the Naiman Desertification Research Center and instrumented with gauges to measure changes in soil height. Depths of erosion and sand accumulation described herein are relative to reference heights established in the late 1980s. An oblong depression (150 80 m with maximum depth 45 –50 cm) eroded by wind was located at the windward margin of the research site. Signs of increased erosion in the depression and increased deposition in the lee of the depression were observed. There was a marked gradient of erosion intensity in the depression and sand accumulation intensity in the lee of the depression. Four parallel sample belts were established along this gradient, running from the bottom to the leeward side of the depression. The width and length of each sample belt was 4 75 m, and the space between each sample belt was 10– 15 m. Seven quadrats (2 2 m) were set up along each belt, and the space between each quadrat was 10– 12 m. Based on the depth of soil eroded or thickness of accumulated sand, the quadrats in each belt were classified into 7 grades or ‘‘classes’’ on an ordinal scale: severe wind erosion (SWE), moderate wind erosion (MWE), light wind erosion (LWE), transition region, light sand accumulation (LSA), moderate sand accumulation (MSA) and severe sand accumulation (SSA) (Table 1). The transition region was omitted from analysis. The original surface soil layer was completely destroyed in severely eroded sites (SWE), and the soil layer was partly destroyed in the moderate and lightly eroded sites. Though there was 4 to 20 cm of accumulated sand leeward of the depression, the soil layer under the deposited sand was not destroyed. In addition, a sample site to the lee of the depression 300 m distant, which was not affected by erosion or sand accumulation, was selected as control farmland (Ctrl) to compare with the other sites. Corn was planted and managed with the same cultural practices across the whole farmland experiment. Planting, fertilization, weeding and other practices were performed by the local farmer under researcher guidance during the experiment period. 2.3. Data collection and analysis
2.2. Experimental design This study was conducted during 2000 to 2001. An open and level farmland area (1000 800 m) was selected for this experiment. This area is part of a long-term monitoring site
In all the quadrats, soil samples were collected from 0- to 20-cm depth after plowing and before seeding in April, 2001 and 2002. Each sample was an aggregate obtained by combining five sub-samples collected from five points in
Table 1 Wind erosion depth and thickness of accumulated sand at sampling sites Quadrats, ordinal
1
Site types
Wind-erosion sites
Degrees
Severe
Moderate
Light
Eroded depth (cm) or thickness (cm)
45 T 2 0
23 T 1 0
10 T 2 0
Values are means T SD.
2
3
4
5
Transition zone
Sand-accumulation sites
0T1 0T1
6
7
8 Ctrl farmland
Light
Moderate
Severe
0 +4 T 1
0 +10 T 2
0 +20 T 1
0 0
H.-L. Zhao et al. / Catena 65 (2006) 71 – 79
each quadrat. Soil bulk density was determined using a soil corer (stainless steel cylinder with volume of 100 cm3) to obtain three samples at each of three depths (0– 5, 5 –10 and 10 –30 cm) in each quadrat (i.e., nine bulk density samples per quadrat). Soil samples were placed in sealed plastic bags and transported to the laboratory. In the laboratory, each sample was thoroughly sieved to 2 mm to remove roots and incorporated litter. Part of each sieved sample was air-dried for analysis of particle size distribution and chemical properties. Soil particle size distribution was determined by the pipette method in a sedimentation cylinder, using Na-hexamethaphosphate as the dispersing agent (Day, 1965). Soil pH was determined with a combination pH electrode (Multiline F/SET-3, Germany) in a 1 : 1 soil – water slurry. Soil organic matter was measured by the K2Cr2O7 –H2SO4 oxidation method of Walkey and Black (Nelson and Sommers, 1982), total N by the Kjeldahl procedure (UDK 140 Automatic Steam Distilling Unit, Automatic Titroline 96, Italy) (ISSCAS, 1978) and total P by UV-1601 Spectrophotometer (HAYASHI Co., Japan), after H2SO4 – HCIO4 digestion (ISSCAS,1978). Soil available N was determined by the alkaline diffusion method, and available P by the Bray method (ISSCAS, 1978). In each quadrat, soil temperature and water content during the growing season were determined by geothermometers (HH82, Exphil Calibration Labs, Bohemia, NY, USA) and hygrometers (TRIME-FM, IMKO, GmbH, Ettlingen, Germany), with an observation interval of 10 days. All data were analyzed using SPSS software. Multiple comparisons and analyses of variance (ANOVA) were used to determine the differences among the treatments (Sokal and Rohlf, 1995).
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3. Results 3.1. Changes in soil particle size distribution and bulk density There was little clay (particles < 0.005 mm) and abundant sand (particles > 0.05 mm) in the Horqin sandy farmland. Sand content was up to 70.2% in the Ctrl sites. Long-term wind erosion increased the sand content significantly, and decreased clay and silt content significantly, in the eroded sites compared with the Ctrl sites ( P < 0.05) (Fig. 1). The sand, silt and clay contents in the severely eroded sites were 115.0%, 71.6% and 40.4% of those in the Ctrl sites. Sand content in the lightly eroded sites was higher than that in the severely eroded sites as a result of some sand, driven by the wind force, creeping from the bottom to the upper side of the depression. Sand accumulation also resulted in significant changes ( P < 0.05) in soil particle size distribution (Fig. 1). Compared to the Ctrl sites, sand and clay contents decreased by 6.7% and 13.1%, and silt increased by 24.3%, in the light sand-accumulation sites (LSA). Sand content increased by 3.7%, and silt and clay decreased by 12.7% and 2.0%, in the severe sand-accumulation sites (SSA). Compared to the wind-eroded sites, silt and clay contents were significantly higher ( P < 0.05) and sand content was significant lower ( P < 0.05) in the sandaccumulation sites, which showed that the effects of sand accumulation on soil particle size distribution were less than those of wind erosion. Although the bulk densities in the 0- to 5-cm soil layer showed some differences among sampling sites (Fig. 2), these were not significant ( P > 0.05) except in the severely
Fig. 1. Soil particle size distribution in sandy farmland affected by long-term wind erosion and sand accumulation in the Horqin sand land of Inner Mongolia. Values are means T SD. Classes: SWE, severe wind erosion; MWE, moderate wind erosion; LWE, light wind erosion; LSA, light sand-accumulation; MSA, moderate sand-accumulation; SSA, severe sand-accumulation; Ctrl, control sites with no erosion or sand accumulation.
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Fig. 2. Soil bulk density at different depths in sandy farmland affected by long-term wind erosion and sand accumulation in the Horqin sand land of Inner Mongolia. Values are means T SD. Classes: SWE, severe wind erosion; MWE, moderate wind erosion; LWE, light wind erosion; LSA, light sand-accumulation; MSA, moderate sand-accumulation; SSA, severe sand-accumulation; Ctrl, control sites with no erosion or sand accumulation. For MWE 10 – 30 cm depth SD = 0.015.
eroded sites ( P < 0.05), where bulk density decreased by 5.3% compared to the Ctrl sites. Compared to the Ctrl sites, the bulk densities in the 5 – 10 cm soil layer increased significantly ( P < 0.05) in the lightly and moderately eroded sites and the moderate sand-accumulation sites, but the changes in the other sites were not significant ( P > 0.05). In the 10 –30 cm soil layer, the bulk densities in the severely eroded sites and the light sandaccumulation sites were significantly lower than in the Ctrl sites ( P < 0.05), but the changes in the other sites
were not significant ( P > 0.05) compared with the Ctrl sites. 3.2. Changes in soil organic C and pH Soil organic C decreased significantly ( P < 0.05) with an increase in the eroded depth (Fig. 3), with decreases of 38.6% and 71.1%, respectively, in the lightly and severely eroded sites compared with the Ctrl sites. Accumulated sand also resulted in a significant decrease in soil organic
Fig. 3. Soil organic C and pH in sandy farmland affected by long-term wind erosion and sand accumulation in the Horqin sand land of Inner Mongolia. Values are means T SD. Classes: SWE, severe wind erosion; MWE, moderate wind erosion; LWE, light wind erosion; LSA, light sand-accumulation; MSA, moderate sand-accumulation; SSA, severe sand-accumulation; Ctrl, control sites with no erosion or sand accumulation.
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Fig. 4. Soil total nutrients in sandy farmland affected by long-term wind erosion and sand accumulation in the Horqin sand land of Inner Mongolia. Values are means T SD. Classes: SWE, severe wind erosion; MWE, moderate wind erosion; LWE, light wind erosion; LSA, light sand-accumulation; MSA, moderate sand-accumulation; SSA, severe sand-accumulation; Ctrl, control sites with no erosion or sand accumulation.
C ( P < 0.05), but the magnitude of decrease was significantly lower than that in the wind-eroded sites ( P < 0.05); organic C decreased by 11.8% and 19.1%, respectively, in the light-and severe sand-accumulation sites, compared to the Ctrl sites. Soil pH increased in eroded areas. The pH value in the severely eroded sites was significantly higher than that in the Ctrl sites ( P < 0.05). Although sand accumulation also resulted in an apparent increase in soil pH (Fig. 3), the
differences were not significant compared with the Ctrl sites ( P > 0.05). 3.3. Changes in N, P and K contents Total N and total P contents decreased significantly ( P < 0.05), while total K tended to increase ( P > 0.05) with an increase in wind erosion depth (Fig. 4). Total N and total P decreased by 67.4% and 31.4% respectively, and total K
Fig. 5. Soil available nutrients in sandy farmland affected by long-term wind erosion and sand accumulation in the Horqin sand land of Inner Mongolia. Values are means T SD. Classes: SWE, severe wind erosion; MWE, moderate wind erosion; LWE, light wind erosion; LSA, light sand-accumulation; MSA, moderate sand-accumulation; SSA, severe sand-accumulation; Ctrl, control sites with no erosion or sand accumulation.
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Table 2 Soil water content (% by weight, drying method) at different depths as affected by long-term wind erosion and sand accumulation in the Horqin sand land of Inner Mongolia 0 – 5 cm depth
SWE MWE LWE LSA MSA SSA Ctrl
5 – 10 cm depth
10 – 30 cm depth
Mean
cv
Max.
Min.
Mean
cv
Max.
Min.
Mean
cv
Max.
Min.
7.6 T 6.6a 7.8 T 6.0a 7.9 T 6.4a 7.4 T 6.0a 7.3 T 5.9a 7.1 T 5.9a 7.8 T 5.9a
0.87 0.78 0.81 0.81 0.81 0.83 0.76
23.1 22.3 23.6 21.9 21.4 21.5 22.1
3.0 3.5 3.4 2.1 2.7 2.1 2.3
9.0 T 6.5a 10.0 T 6.0a 11.5 T 6.2a 9.6 T 6.4a 9.9 T 6.0a 10.0 T 6.1a 12.0 T 7.6a
0.72 0.60 0.54 0.67 0.61 0.61 0.63
22.6 23.2 25.7 25.1 23.5 23.2 29.6
4.7 6.7 5.7 4.5 4.0 4.3 3.6
8.8 T 6.3a 10.2 T 6.2a 13.7 T 5.6b 21.5 T 6.6cd 18.9 T 6.1c 18.1 T 6.2c 26.3 T 8.8d
0.71 0.61 0.41 0.31 0.32 0.34 0.33
23.3 23.8 26.6 34.6 32.3 29.9 40.7
4.1 5.6 7.8 11.8 10.0 6.6 11.6
Values are means T SD. Values with the same letters are not significantly different at P 0.05. Classes: SWE, severe wind erosion; MWE, moderate wind erosion; LWE, light wind erosion; LSA, light sand-accumulation; MSA, moderate sandaccumulation; SSA, severe sand-accumulation; Ctrl, control sites with no erosion or sand accumulation.
increased by 12.2%, in the severely eroded sites compared to the Ctrl sites. Although total N and total P showed some decrease in the accumulated-sand sites compared to the Ctrl sites, the difference was not significant ( P > 0.05), and total K did not show any changes. Average content of total N and total P were higher by 67.4% and 17.6% in the accumulated-sand sites than in the wind-erosion sites, but the average content of total K was lower by 7.7%. Available N content decreased significantly ( P < 0.05) with an increase in both wind erosion depth and accumulated sand thickness (Fig. 5). Compared to the Ctrl sites, available N decreased by 52.8% and 64.5%, respectively, in the lightly and severely eroded sites, and decreased by 36.7% and 52.5%, respectively, in the light-and severe sandaccumulation sites. Available P content decreased significantly ( P < 0.05) with increasing wind erosion depth, with decreases of 38.8% in the severely eroded sites compared to the Ctrl sites. Although available P content differed between
the accumulated-sand sites and the Ctrl sites, the difference was not significant ( P > 0.05) except for the moderate sandaccumulation sites. Compared to the Ctrl sites, available K content was significantly lower ( P < 0.05) in all winderoded and sand-accumulation sites except for the moderate sand-accumulation sites. Available K decreased by 29.1% and 43.8%, respectively, in the lightly and severely eroded sites, and by 22.0% and 13.8%, respectively, in the lightand severe sand-accumulation sites. 3.4. Changes in soil water and temperature status Soil water content was calculated as (wet weight dry weight / wet weight) 100%. Wind erosion and sand accumulation did not result in significant changes in average soil water content in the 0– 5 or 5– 10 cm soil layers at any of the sites (Table 2), but average soil water decreased significantly ( P < 0.05) in the 10 –30 cm soil layer with an
Fig. 6. Soil temperature at different depths in sandy farmland affected by long-term wind erosion and sand accumulation in the Horqin sand land of Inner Mongolia. Values are means T SD. Classes: SWE, severe wind erosion; MWE, moderate wind erosion; LWE, light wind erosion; LSA, light sand-accumulation; MSA, moderate sand-accumulation; SSA, severe sand-accumulation; Ctrl, control sites with no erosion or sand accumulation.
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increase in wind erosion depth and accumulated sand thickness. Compared to the Ctrl sites, soil water content decreased by 47.9% and 66.5% in the lightly and severely eroded sites, and by 18.3% and 31.2%, respectively, in the light- and severe sand-accumulation sites (10 – 30 cm depth). Importantly, the minimum soil moisture in the 10 – 30 cm layer was lower than the wilting point of local corn in the moderately and severely eroded sites (Zhao et al., 1996), which was very unfavorable for corn growth and yield. Average temperatures at the ground surface during the growing season increased significantly ( P < 0.05) in the wind-erosion sites and accumulated-sand sites compared to the Ctrl sites, with increases from 1.6 to 2.2 -C in the winderoded sites and from 2.8 to 4.0-C in the accumulated-sand sites (Fig. 6). Although there were some changes in soil temperature in the 5 –20 cm layer in both the wind-eroded sites and the accumulated-sand sites compared to the Ctrl sites, the differences were not significant ( P > 0.05).
4. Discussion 4.1. Interrelations among soil properties Soil is a material with multiple properties, including physical, chemical, and biological properties (Su et al., 2002), and there are interrelations and interactions among these properties (Lowery et al., 1995). Thus, when some soil properties change, related soil factors may be affected (Lowery et al., 1995; Grieve, 2001). In the present research, a correlative analysis showed that in the change processes of the soil environment, there were significant ( P < 0.05) positive correlations between soil clay content and soil organic C (r 2 = 0.95), total N (r 2 = 0.93), total P (r 2 = 0.87), and water content (r 2 = 0.89) (Table 3). There were significant negative correlations between clay content and pH (r 2 = 0.98), and total K (r 2 = 0.94). This showed that loss of soil clay resulted in a reduction of nutrients, and soil coarseness resulted in a decrease in soil water-holding capacity and an increase in soil alkalinity. This is in agreement with observations by Li et al. (2004) and Su
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and Zhao (2003) in the Horqin sand land. The correlation analysis also showed that there were significant ( P < 0.05) positive correlations between pH values and organic C, total N and total P. There were also significant positive correlations between organic C and total N, total P, and soil moisture (Table 3). But there was a significant negative correlation ( P < 0.001) between pH and soil water (Table 3). These values suggest that there is a significant interaction among soil moisture, nutrients and acidity, and they together are controlled by soil particle size distribution and organic matter content, which is in agreement with research by Su and Zhao (2003) and Larney et al. (1998). Changes in soil temperature did not show significant correlation with soil moisture, soil particle size distribution or nutrients ( P > 0.05). 4.2. Wind erosion and sand accumulation effects on the soil environment It is well known that wind erosion can cause a loss of fine soil particles and an increase in soil coarseness (Gomes et al., 2003; Su et al., 2002). Some scientists have suggested also that soil structure is a dominant factor in organic matter breakdown within soils. Loss of soil fine particles could result in loss of soil organic matter and poor soil structure because most organic matter is combined with soil fine particles (Garcia and Hernandez, 1996; Su and Zhao, 2003; Lopez, 1998). This conclusion was confirmed by our study, in which soil clay and organic C decreased with an increase in erosion depth, by 59.6% and 71.2%, respectively, in the severely eroded sites compared to the non-eroded control sites. Regression analysis showed that there was an exponential decline in soil organic C (SOC) content with a loss of clay (v, %), described by the function: SOC content ðg kg 1 Þ ¼ 1:43540:6365 P < 0:0001; r 2 ¼ 0:97 Wezel et al. (2000) indicate that in arid and semiarid ecosystems, soil organic matter concentration is one of the most important factors influencing the storage of nutrients
Table 3 Pearson correlation among soil properties
Sand pH Org. C Total N Total P Total K Av. N Av. P Av. K Moist. Temp.
Clay
Sand
pH
Org. C
Total N
Total P
Total K
Av. N
Av. P
Av. K
Moist.
0.982*** 0.975*** 0.950** 0.928** 0.886** 0.935** 0.626 0.501 0.930** 0.890** 0.736
0.969*** 0.931** 0.914** 0.880** 0.950*** 0.619 0.552 0.878** 0.885** 0.711
0.983*** 0.972*** 0.958*** 0.931** 0.764* 0.525 0.945** 0.968*** 0.606
0.992*** 0.952*** 0.925** 0.752 0.608 0.968*** 0.966*** 0.620
0.952*** 0.937** 0.755* 0.644 0.965*** 0.970*** 0.613
0.879* 0.148 0.439 0.886* 0.982*** 0.402
0.595 0.665 0.871* 0.865 0.740
0.148 0.675 0.876* 0.029
0.566 0.450 0.652
0.925*** 0.675
0.434
*Correlation is significant at the 0.05 level; **significant at the 0.01 level; ***significant at the 0.001 level.
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and water in nutrient-poor sandy soils. In our study, soil nutrients and soil moisture decreased significantly with a reduction in organic C and clay content, with total N and available N decreasing by 67.4% and 64.5%, and total P and available P decreasing by 31.4% and 38.8%, respectively, and average soil moisture decreasing by 51.8%, in the severely eroded farmland compared to the Ctrl farmland. In particular, the lowest soil moisture content during the dry season was lower than the wilting point for local corn. This indicated that soil nutrient status and water-holding capacity worsened markedly after the loss of clay and soil organic C by long term wind erosion, which was evidently unfavorable for crop growth (Lal, 1998; Larney et al., 1998). Lowery et al. (1995) and Larney et al. (1998) had confirmed that the consequences of wind erosion include a reduction in crop production by selective removal of the finest soil particles with nutrients and organic matter, a reduction in soil water-holding capacity, and increased degradation of soil structure. Thus wind erosion has been considered one of the main limiting factors for plant productivity in some areas (Ettershank et al., 1978). Although sand accumulation also had a significant effect on particle size distribution, nutrient content and waterholding capacity, this effect was significantly less than that of wind erosion ( P < 0.05). For example, in the severe sandaccumulation sites, the content of clay, organic C, total N, total P and soil water decreased by 2.0%, 19.3%, 21.7%, 13.7% and 26.7%, respectively, compared with the Ctrl sites, while in the severely eroded sites the same factors decreased by 59.6%, 71.2%, 68.8%, 31.6% and 66.4%. It is evident that wind erosion can result in a loss of the finest soil particles and soil nutrients, and in degradation of soil structure (Lowery et al., 1995; Larney et al., 1998), but sand accumulation does not result in any loss of original soil clay particles or nutrients, only in a reduction of clay and nutrient concentration because of additional sand deposited in the soil. Moreover, the original cultivated surface layer can be destroyed by continual wind erosion, but this phenomenon does not occur in the sand-accumulation areas. These results are in agreement with observations by Su et al. (2002), Zhao et al. (2003), and Gomes et al. (2003).
5. Conclusion The research results showed that long-term wind erosion significantly changed some soil properties, including increased sand content and pH values, and decreased clay content, organic matter, nutrients, and soil water. These changes resulted in soil barrenness, dryness and coarseness, and caused deterioration of land resources. In particular, severe wind erosion not only resulted in a rapid decrease of soil nutrients and water-holding capacity, but also destroyed the surface soil layer and led to exposure of the sandy parent material to wind erosion, which could lead to more intense land degradation. Some sand-
accumulation sites showed a decrease in soil nutrient concentration and water content, but these decreases were significantly less than in wind-eroded sites. However, the effects of more severe sand accumulation on farmland soil need to be further studied.
Acknowledgements The authors are grateful to the anonymous reviewers for their critical review and comments on drafts of this manuscript. This research was funded as one of the Chinese National Fund Projects (40471004).
References ˚ hman, R., 2003. Wind erosion on Ba¨rring, L., Jo¨nsson, P., Mattsson, J.O., A arable land in Scania, Sweden and the relation to the wind climate—a review. Catena 52, 173 – 190. Day, P.R., 1965. Particle fractionation and particle-size distribution. In: Black, C.A., Evans, D.D., White, J.L., Clark, F.E. (Eds.), Methods of Soil Analysis, Agronomy, vol. 9. ASA, Madison, WI, pp. 548 – 549. Ettershank, G., Ettershank, J.A., Bryant, M., Withford, W.G., 1978. Effect of nitrogen fertilization on primary production in a Chihuahuan Desert ecosystem. Journal of Arid Environments 1, 135 – 139. Garcia, C., Hernandez, T., 1996. Organic matter in bare soils of the Mediterranean region with a semiarid climate. Arid Soil Research and Rehabilitation 10, 31 – 41. Gomes, L., Arrue, J.L., Lopez, M.V., Sterk, G., Richard, D., Gracia, R., Sabre, J.M., Gaudichet, A., Frangi, J.P., 2003. Wind erosion in a semiarid area of Spain: the WELSONS project. Catena 52, 235 – 256. Grieve, C.I., 2001. Human impacts on soil properties and their implications for the sensitivity of the soil system in Scotland. Catena 42, 361 – 374. Hennessy, T., Kies, B., 1986. Soil sorting by forty-five years of wind erosion on a southern New Mexico range. Soil Science Society of America Journal 56, 391 – 394. Institute of Soil Science, Chinese Academy of Sciences (ISSCAS), 1978. Physical and Chemical Analysis Methods of Soils. China Shanghai Science Technology Press, pp. 7 – 59. Lal, R., 1998. Soil erosion impact on agronomic productivity and environment quality. Critical Reviews in Plant Sciences 17, 319 – 464. Larney, F.J., Bullock, M.S., Janzen, H.H., Ellert, B.H., Olson, E.C.S., 1998. Wind erosion effects on nutrient redistribution and soil productivity. Journal of Soil and Water Conservation 53, 133 – 140. Li, F.R., Zhao, L.Y., Zhang, T.H., 2004. Wind erosion and airborne dust deposition in farmland during spring in the Horqin sandy land of eastern Inner Mongolia, China. Soil and Tillage Research 75, 121 – 130. Lopez, M.V., 1998. Wind erosion in agricultural soil: an example of limited supply of particles available for erosion. Catena 33, 17 – 28. Lowery, B., Swan, J., Schumacher, T., Jones, A., 1995. Physical properties of selected soils by erosion class. Journal of Soil and Water Conservation 50, 306 – 311. Nelson, D.W., Sommers, L.E., 1982. Total carbon, organic carbon and organic matter. In: Page, A.L., Miller, R.H., Keeney, D.R. (Eds.), Methods of Soil Analysis, 2nd edition. Agronomy, Madison, WI, USA. Part 2, pp. 539 – 577. Okin, G.S., Murray, B., Schlesinger, W.H., 2001. Degradation of sandy arid shrub-land environments: observations, process modeling, and management implications. Journal of Arid Environments 47 (2), 123 – 144. Pimentel, D., Harvey, P., Sinclair, K., Kurz, D., Menair, M., Crist, S., Shpritz, L., Fitton, L., Saffouri, R., Blair, R., 1995. Environmental and economic costs of soil erosion and conservation benefits. Science 267, 1117 – 1123.
H.-L. Zhao et al. / Catena 65 (2006) 71 – 79 Saxton, K.E., 1995. Wind erosion and its impact on off-site air quality in the Columbia Plateau—an integrated research plan. Transactions of the ASAE 38, 1031 – 1038. Sokal, R.R., Rohlf, F.J., 1995. Biometry. W. H. Freeman, New York. Su, Y.Z., Zhao, H.L., 2003. Losses of soil organic carbon and nitrogen and their mechanisms in the desertification process of farmlands in Horqin sandy land. Agriculture Sciences in China 2 (8), 890 – 897. Su, Y.Z., Zhao, H.L., Zhang, T.H., Li, Y.L., 2002. Processes and characteristics of soil degradation in rainfed farmland in the Horqin sandy land. Journal of Soil and Water Conservation 16, 25 – 28. Wang, T., 2000. Land use and sandy desertification in north China. Journal of Desert Research 20 (2), 103 – 113 (in Chinese). Wezel, A., Rajot, J.L., Herbring, C., 2000. Influence of shrubs on soil characteristics and their function in Sahelian agro-ecosystems in semiarid Niger. Journal of Arid Environments 44, 383 – 398.
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Xu, B., Liou, X.M., 1997. Field study on wind – sand flow affecting crop seedling and farm soil erosion. Journal of Desert Research 17 (1), 78 – 84 (in Chinese). Zhao, H.L, Huang, X.W., Heng, Z.Y., 1996. Study on desertification processes in sandy farmland in Horqin region, China. Acta Pedologica Sinica 33 (3), 238 – 241. Zhao, H.L., Zhang, T.H., Zhou, R.L., 2003. Soil environment and productivity formation processes of corn in five types of farmland of Horqin sandy land. Acta Pedologica Sinica 40 (2), 194 – 199. Zhu, Z.D., Chen, G.T., 1994. Sandy Desertification in China. Science Press, Beijing, pp. 240 – 253 (in Chinese).
Wind erosion and sand accumulation effects on soil properties in Horqin Sandy Farmland, Inner Mongolia Ha-Lin Zhao a, Xiao-Yong Yi a, Rui-Lian Zhou a, Xue-Yong Zhao a, Tong-Hui Zhang a, Sam Drake b,* a
Cold and Arid Regions Environment and Engineering Institute, Chinese Academy of Sciences, 260 Donggang West Road, 730000, Lanzhou, P.R. China b Office of Arid Lands Studies, University of Arizona, 1955 E. 6th Street, Tucson, AZ 85719, USA Received 9 March 2004; received in revised form 14 September 2005; accepted 3 October 2005
Abstract Rain-fed agriculture is widespread in Inner Mongolia, northern China, where wind erosion of farmland is very common because of sandy soil and dry, windy weather. However, very little is known about the effects of wind erosion on soil physical and chemical properties in this region. A field experiment was conducted in sandy farmland, where erosional and depositional gradients were established to evaluate the effects of wind erosion and leeward sand accumulation on soil texture, nutrient content, soil water, and soil temperature. The research showed that long term wind erosion could result in significant soil coarseness, infertility and dryness. Severe erosion reduced clay by 59.6%, organic C by 71.2%, total N by 67.4%, total P by 31.4%, available N by 64.5%, available P by 38.8%, and average soil water content by 51.8%, compared with non-eroded farmland in the study region. The sand fraction (particles > 0.05 mm), pH and ground-surface temperature increased by 6.2%, 3.7%, and 2.2 -C, respectively. Accumulated sand also caused a decrease in nutrients and soil water content. Under severe sand accumulation, clay was reduced by 2.0%, organic C by 19.3%, total N by 21.7%, total P by 13.7%, available N by 52.5%, and average soil water content by 26.6%. The sand fraction, pH, available P, and ground-surface temperature increased by 0.2%, 0.9%, 5.8% and 2.8 -C, respectively. D 2005 Elsevier B.V. All rights reserved. Keywords: Wind erosion; Particle size distribution; Soil nutrients; Soil moisture; Sandy farmland; Inner Mongolia
1. Introduction Wind erosion not only results in destruction of soil structure, but also affects land production potential (Lopez, 1998). Thus wind erosion is considered to be a principal mechanism of land degradation (Hennessy and Kies, 1986; Okin et al., 2001) and is one of the most serious environmental and agricultural problems in many arid and semiarid agricultural regions of the world (Gomes et al., 2003). Although it is not a new phenomenon, wind erosion is currently recognized as a major source of environmental degradation. Areas of wind erosion have increased, and current knowledge of its environmental and economic impacts suggests that appropriate measures need to be taken for soil protection (Pimentel et al., 1995; Saxton, 1995). * Corresponding author. Tel.: +1 520 621 4501; fax: +1 520 621 3816. E-mail address: [email protected] (S. Drake). 0341-8162/$ - see front matter D 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.catena.2005.10.001
Research on wind erosion has increased in recent years (Gomes et al., 2003). Farmland soils are vulnerable to erosion by wind in arid and semiarid regions because such soils are relatively coarse-grained and generally lack crop coverage in the windy season (Su and Zhao, 2003; Li et al., 2004). Therefore, there is a need for additional studies of the characteristics and management of this kind of farmland (Ba¨rring et al., 2003; Larney et al., 1998). Over the last 50 years in China, about 9.1 107 ha of farmland have been damaged by wind erosion each year, and 6.7 106 ha of farmland have been buried by mobile dunes, mostly in the sandy rain-fed agricultural regions of Inner Mongolia, northern China (Wang, 2000; Zhao et al., 2003). To understand the effects of wind erosion on the ecoenvironment, researchers have investigated the mechanisms of erosion on different types of farmland and the spatial distribution of eroded farmland in this area (Zhu and Chen, 1994; Wang, 2000), the characteristics of soil degradation
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caused by wind erosion (Su et al., 2002; Su and Zhao, 2003), and the effects of wind-blown sand on crop growth (Xu and Liou, 1997; Li et al., 2004). However, some effects of wind erosion are still not well known, particularly the effect of accumulated sand on the agricultural soil environment in semi-arid areas of China (Zhao et al., 2003). Thus, the objectives of this study were to analyze changes in the physical and chemical properties of agricultural soils due to long-term wind erosion and leeward sand accumulation, and to evaluate the relationships among different soil properties and soil degradation processes.
2. Materials and methods 2.1. Study area The study area is located in the Horqin sand land (42- 55V N, 120- 42VE, 345 m above sea level) in the eastern part of Inner Mongolia, which belongs to the continental semi-arid monsoon climate in the temperate zone. Mean annual precipitation is 366 mm, mean annual potential evaporation is 1935 mm, and the mean annual temperature is 6.8 - C. The annual frost-free period is about 130– 150 days. The average annual wind speed is 3.4 m s 1 and mean wind speed in the wind erosion season (spring) is 4.3 m s 1. The landscape in this region is characterized by different types of dunes alternating with gently undulating lowland areas. The thickness of the soil layer in the farmlands is about 30 – 45 cm and the soil consists mainly of coarse sand and silt; the C Horizon is sand aggraded during the Quaternary period. Corn (Zea mays L.) monoculture dominates the cultivated land. In this system, the corn is planted at the end of April and harvested at the end of September, leaving the soil bare for about 7 months, from October through April of the following year. Wind erosion is very pronounced during the spring season. From the thawing of the frozen surface in mid-March until the sowing of crops at the end of April, the loose soil surface is dry and bare, and thus extremely susceptible to wind erosion (Li et al., 2004).
operated by the Naiman Desertification Research Center and instrumented with gauges to measure changes in soil height. Depths of erosion and sand accumulation described herein are relative to reference heights established in the late 1980s. An oblong depression (150 80 m with maximum depth 45 –50 cm) eroded by wind was located at the windward margin of the research site. Signs of increased erosion in the depression and increased deposition in the lee of the depression were observed. There was a marked gradient of erosion intensity in the depression and sand accumulation intensity in the lee of the depression. Four parallel sample belts were established along this gradient, running from the bottom to the leeward side of the depression. The width and length of each sample belt was 4 75 m, and the space between each sample belt was 10– 15 m. Seven quadrats (2 2 m) were set up along each belt, and the space between each quadrat was 10– 12 m. Based on the depth of soil eroded or thickness of accumulated sand, the quadrats in each belt were classified into 7 grades or ‘‘classes’’ on an ordinal scale: severe wind erosion (SWE), moderate wind erosion (MWE), light wind erosion (LWE), transition region, light sand accumulation (LSA), moderate sand accumulation (MSA) and severe sand accumulation (SSA) (Table 1). The transition region was omitted from analysis. The original surface soil layer was completely destroyed in severely eroded sites (SWE), and the soil layer was partly destroyed in the moderate and lightly eroded sites. Though there was 4 to 20 cm of accumulated sand leeward of the depression, the soil layer under the deposited sand was not destroyed. In addition, a sample site to the lee of the depression 300 m distant, which was not affected by erosion or sand accumulation, was selected as control farmland (Ctrl) to compare with the other sites. Corn was planted and managed with the same cultural practices across the whole farmland experiment. Planting, fertilization, weeding and other practices were performed by the local farmer under researcher guidance during the experiment period. 2.3. Data collection and analysis
2.2. Experimental design This study was conducted during 2000 to 2001. An open and level farmland area (1000 800 m) was selected for this experiment. This area is part of a long-term monitoring site
In all the quadrats, soil samples were collected from 0- to 20-cm depth after plowing and before seeding in April, 2001 and 2002. Each sample was an aggregate obtained by combining five sub-samples collected from five points in
Table 1 Wind erosion depth and thickness of accumulated sand at sampling sites Quadrats, ordinal
1
Site types
Wind-erosion sites
Degrees
Severe
Moderate
Light
Eroded depth (cm) or thickness (cm)
45 T 2 0
23 T 1 0
10 T 2 0
Values are means T SD.
2
3
4
5
Transition zone
Sand-accumulation sites
0T1 0T1
6
7
8 Ctrl farmland
Light
Moderate
Severe
0 +4 T 1
0 +10 T 2
0 +20 T 1
0 0
H.-L. Zhao et al. / Catena 65 (2006) 71 – 79
each quadrat. Soil bulk density was determined using a soil corer (stainless steel cylinder with volume of 100 cm3) to obtain three samples at each of three depths (0– 5, 5 –10 and 10 –30 cm) in each quadrat (i.e., nine bulk density samples per quadrat). Soil samples were placed in sealed plastic bags and transported to the laboratory. In the laboratory, each sample was thoroughly sieved to 2 mm to remove roots and incorporated litter. Part of each sieved sample was air-dried for analysis of particle size distribution and chemical properties. Soil particle size distribution was determined by the pipette method in a sedimentation cylinder, using Na-hexamethaphosphate as the dispersing agent (Day, 1965). Soil pH was determined with a combination pH electrode (Multiline F/SET-3, Germany) in a 1 : 1 soil – water slurry. Soil organic matter was measured by the K2Cr2O7 –H2SO4 oxidation method of Walkey and Black (Nelson and Sommers, 1982), total N by the Kjeldahl procedure (UDK 140 Automatic Steam Distilling Unit, Automatic Titroline 96, Italy) (ISSCAS, 1978) and total P by UV-1601 Spectrophotometer (HAYASHI Co., Japan), after H2SO4 – HCIO4 digestion (ISSCAS,1978). Soil available N was determined by the alkaline diffusion method, and available P by the Bray method (ISSCAS, 1978). In each quadrat, soil temperature and water content during the growing season were determined by geothermometers (HH82, Exphil Calibration Labs, Bohemia, NY, USA) and hygrometers (TRIME-FM, IMKO, GmbH, Ettlingen, Germany), with an observation interval of 10 days. All data were analyzed using SPSS software. Multiple comparisons and analyses of variance (ANOVA) were used to determine the differences among the treatments (Sokal and Rohlf, 1995).
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3. Results 3.1. Changes in soil particle size distribution and bulk density There was little clay (particles < 0.005 mm) and abundant sand (particles > 0.05 mm) in the Horqin sandy farmland. Sand content was up to 70.2% in the Ctrl sites. Long-term wind erosion increased the sand content significantly, and decreased clay and silt content significantly, in the eroded sites compared with the Ctrl sites ( P < 0.05) (Fig. 1). The sand, silt and clay contents in the severely eroded sites were 115.0%, 71.6% and 40.4% of those in the Ctrl sites. Sand content in the lightly eroded sites was higher than that in the severely eroded sites as a result of some sand, driven by the wind force, creeping from the bottom to the upper side of the depression. Sand accumulation also resulted in significant changes ( P < 0.05) in soil particle size distribution (Fig. 1). Compared to the Ctrl sites, sand and clay contents decreased by 6.7% and 13.1%, and silt increased by 24.3%, in the light sand-accumulation sites (LSA). Sand content increased by 3.7%, and silt and clay decreased by 12.7% and 2.0%, in the severe sand-accumulation sites (SSA). Compared to the wind-eroded sites, silt and clay contents were significantly higher ( P < 0.05) and sand content was significant lower ( P < 0.05) in the sandaccumulation sites, which showed that the effects of sand accumulation on soil particle size distribution were less than those of wind erosion. Although the bulk densities in the 0- to 5-cm soil layer showed some differences among sampling sites (Fig. 2), these were not significant ( P > 0.05) except in the severely
Fig. 1. Soil particle size distribution in sandy farmland affected by long-term wind erosion and sand accumulation in the Horqin sand land of Inner Mongolia. Values are means T SD. Classes: SWE, severe wind erosion; MWE, moderate wind erosion; LWE, light wind erosion; LSA, light sand-accumulation; MSA, moderate sand-accumulation; SSA, severe sand-accumulation; Ctrl, control sites with no erosion or sand accumulation.
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Fig. 2. Soil bulk density at different depths in sandy farmland affected by long-term wind erosion and sand accumulation in the Horqin sand land of Inner Mongolia. Values are means T SD. Classes: SWE, severe wind erosion; MWE, moderate wind erosion; LWE, light wind erosion; LSA, light sand-accumulation; MSA, moderate sand-accumulation; SSA, severe sand-accumulation; Ctrl, control sites with no erosion or sand accumulation. For MWE 10 – 30 cm depth SD = 0.015.
eroded sites ( P < 0.05), where bulk density decreased by 5.3% compared to the Ctrl sites. Compared to the Ctrl sites, the bulk densities in the 5 – 10 cm soil layer increased significantly ( P < 0.05) in the lightly and moderately eroded sites and the moderate sand-accumulation sites, but the changes in the other sites were not significant ( P > 0.05). In the 10 –30 cm soil layer, the bulk densities in the severely eroded sites and the light sandaccumulation sites were significantly lower than in the Ctrl sites ( P < 0.05), but the changes in the other sites
were not significant ( P > 0.05) compared with the Ctrl sites. 3.2. Changes in soil organic C and pH Soil organic C decreased significantly ( P < 0.05) with an increase in the eroded depth (Fig. 3), with decreases of 38.6% and 71.1%, respectively, in the lightly and severely eroded sites compared with the Ctrl sites. Accumulated sand also resulted in a significant decrease in soil organic
Fig. 3. Soil organic C and pH in sandy farmland affected by long-term wind erosion and sand accumulation in the Horqin sand land of Inner Mongolia. Values are means T SD. Classes: SWE, severe wind erosion; MWE, moderate wind erosion; LWE, light wind erosion; LSA, light sand-accumulation; MSA, moderate sand-accumulation; SSA, severe sand-accumulation; Ctrl, control sites with no erosion or sand accumulation.
H.-L. Zhao et al. / Catena 65 (2006) 71 – 79
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Fig. 4. Soil total nutrients in sandy farmland affected by long-term wind erosion and sand accumulation in the Horqin sand land of Inner Mongolia. Values are means T SD. Classes: SWE, severe wind erosion; MWE, moderate wind erosion; LWE, light wind erosion; LSA, light sand-accumulation; MSA, moderate sand-accumulation; SSA, severe sand-accumulation; Ctrl, control sites with no erosion or sand accumulation.
C ( P < 0.05), but the magnitude of decrease was significantly lower than that in the wind-eroded sites ( P < 0.05); organic C decreased by 11.8% and 19.1%, respectively, in the light-and severe sand-accumulation sites, compared to the Ctrl sites. Soil pH increased in eroded areas. The pH value in the severely eroded sites was significantly higher than that in the Ctrl sites ( P < 0.05). Although sand accumulation also resulted in an apparent increase in soil pH (Fig. 3), the
differences were not significant compared with the Ctrl sites ( P > 0.05). 3.3. Changes in N, P and K contents Total N and total P contents decreased significantly ( P < 0.05), while total K tended to increase ( P > 0.05) with an increase in wind erosion depth (Fig. 4). Total N and total P decreased by 67.4% and 31.4% respectively, and total K
Fig. 5. Soil available nutrients in sandy farmland affected by long-term wind erosion and sand accumulation in the Horqin sand land of Inner Mongolia. Values are means T SD. Classes: SWE, severe wind erosion; MWE, moderate wind erosion; LWE, light wind erosion; LSA, light sand-accumulation; MSA, moderate sand-accumulation; SSA, severe sand-accumulation; Ctrl, control sites with no erosion or sand accumulation.
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Table 2 Soil water content (% by weight, drying method) at different depths as affected by long-term wind erosion and sand accumulation in the Horqin sand land of Inner Mongolia 0 – 5 cm depth
SWE MWE LWE LSA MSA SSA Ctrl
5 – 10 cm depth
10 – 30 cm depth
Mean
cv
Max.
Min.
Mean
cv
Max.
Min.
Mean
cv
Max.
Min.
7.6 T 6.6a 7.8 T 6.0a 7.9 T 6.4a 7.4 T 6.0a 7.3 T 5.9a 7.1 T 5.9a 7.8 T 5.9a
0.87 0.78 0.81 0.81 0.81 0.83 0.76
23.1 22.3 23.6 21.9 21.4 21.5 22.1
3.0 3.5 3.4 2.1 2.7 2.1 2.3
9.0 T 6.5a 10.0 T 6.0a 11.5 T 6.2a 9.6 T 6.4a 9.9 T 6.0a 10.0 T 6.1a 12.0 T 7.6a
0.72 0.60 0.54 0.67 0.61 0.61 0.63
22.6 23.2 25.7 25.1 23.5 23.2 29.6
4.7 6.7 5.7 4.5 4.0 4.3 3.6
8.8 T 6.3a 10.2 T 6.2a 13.7 T 5.6b 21.5 T 6.6cd 18.9 T 6.1c 18.1 T 6.2c 26.3 T 8.8d
0.71 0.61 0.41 0.31 0.32 0.34 0.33
23.3 23.8 26.6 34.6 32.3 29.9 40.7
4.1 5.6 7.8 11.8 10.0 6.6 11.6
Values are means T SD. Values with the same letters are not significantly different at P 0.05. Classes: SWE, severe wind erosion; MWE, moderate wind erosion; LWE, light wind erosion; LSA, light sand-accumulation; MSA, moderate sandaccumulation; SSA, severe sand-accumulation; Ctrl, control sites with no erosion or sand accumulation.
increased by 12.2%, in the severely eroded sites compared to the Ctrl sites. Although total N and total P showed some decrease in the accumulated-sand sites compared to the Ctrl sites, the difference was not significant ( P > 0.05), and total K did not show any changes. Average content of total N and total P were higher by 67.4% and 17.6% in the accumulated-sand sites than in the wind-erosion sites, but the average content of total K was lower by 7.7%. Available N content decreased significantly ( P < 0.05) with an increase in both wind erosion depth and accumulated sand thickness (Fig. 5). Compared to the Ctrl sites, available N decreased by 52.8% and 64.5%, respectively, in the lightly and severely eroded sites, and decreased by 36.7% and 52.5%, respectively, in the light-and severe sandaccumulation sites. Available P content decreased significantly ( P < 0.05) with increasing wind erosion depth, with decreases of 38.8% in the severely eroded sites compared to the Ctrl sites. Although available P content differed between
the accumulated-sand sites and the Ctrl sites, the difference was not significant ( P > 0.05) except for the moderate sandaccumulation sites. Compared to the Ctrl sites, available K content was significantly lower ( P < 0.05) in all winderoded and sand-accumulation sites except for the moderate sand-accumulation sites. Available K decreased by 29.1% and 43.8%, respectively, in the lightly and severely eroded sites, and by 22.0% and 13.8%, respectively, in the lightand severe sand-accumulation sites. 3.4. Changes in soil water and temperature status Soil water content was calculated as (wet weight dry weight / wet weight) 100%. Wind erosion and sand accumulation did not result in significant changes in average soil water content in the 0– 5 or 5– 10 cm soil layers at any of the sites (Table 2), but average soil water decreased significantly ( P < 0.05) in the 10 –30 cm soil layer with an
Fig. 6. Soil temperature at different depths in sandy farmland affected by long-term wind erosion and sand accumulation in the Horqin sand land of Inner Mongolia. Values are means T SD. Classes: SWE, severe wind erosion; MWE, moderate wind erosion; LWE, light wind erosion; LSA, light sand-accumulation; MSA, moderate sand-accumulation; SSA, severe sand-accumulation; Ctrl, control sites with no erosion or sand accumulation.
H.-L. Zhao et al. / Catena 65 (2006) 71 – 79
increase in wind erosion depth and accumulated sand thickness. Compared to the Ctrl sites, soil water content decreased by 47.9% and 66.5% in the lightly and severely eroded sites, and by 18.3% and 31.2%, respectively, in the light- and severe sand-accumulation sites (10 – 30 cm depth). Importantly, the minimum soil moisture in the 10 – 30 cm layer was lower than the wilting point of local corn in the moderately and severely eroded sites (Zhao et al., 1996), which was very unfavorable for corn growth and yield. Average temperatures at the ground surface during the growing season increased significantly ( P < 0.05) in the wind-erosion sites and accumulated-sand sites compared to the Ctrl sites, with increases from 1.6 to 2.2 -C in the winderoded sites and from 2.8 to 4.0-C in the accumulated-sand sites (Fig. 6). Although there were some changes in soil temperature in the 5 –20 cm layer in both the wind-eroded sites and the accumulated-sand sites compared to the Ctrl sites, the differences were not significant ( P > 0.05).
4. Discussion 4.1. Interrelations among soil properties Soil is a material with multiple properties, including physical, chemical, and biological properties (Su et al., 2002), and there are interrelations and interactions among these properties (Lowery et al., 1995). Thus, when some soil properties change, related soil factors may be affected (Lowery et al., 1995; Grieve, 2001). In the present research, a correlative analysis showed that in the change processes of the soil environment, there were significant ( P < 0.05) positive correlations between soil clay content and soil organic C (r 2 = 0.95), total N (r 2 = 0.93), total P (r 2 = 0.87), and water content (r 2 = 0.89) (Table 3). There were significant negative correlations between clay content and pH (r 2 = 0.98), and total K (r 2 = 0.94). This showed that loss of soil clay resulted in a reduction of nutrients, and soil coarseness resulted in a decrease in soil water-holding capacity and an increase in soil alkalinity. This is in agreement with observations by Li et al. (2004) and Su
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and Zhao (2003) in the Horqin sand land. The correlation analysis also showed that there were significant ( P < 0.05) positive correlations between pH values and organic C, total N and total P. There were also significant positive correlations between organic C and total N, total P, and soil moisture (Table 3). But there was a significant negative correlation ( P < 0.001) between pH and soil water (Table 3). These values suggest that there is a significant interaction among soil moisture, nutrients and acidity, and they together are controlled by soil particle size distribution and organic matter content, which is in agreement with research by Su and Zhao (2003) and Larney et al. (1998). Changes in soil temperature did not show significant correlation with soil moisture, soil particle size distribution or nutrients ( P > 0.05). 4.2. Wind erosion and sand accumulation effects on the soil environment It is well known that wind erosion can cause a loss of fine soil particles and an increase in soil coarseness (Gomes et al., 2003; Su et al., 2002). Some scientists have suggested also that soil structure is a dominant factor in organic matter breakdown within soils. Loss of soil fine particles could result in loss of soil organic matter and poor soil structure because most organic matter is combined with soil fine particles (Garcia and Hernandez, 1996; Su and Zhao, 2003; Lopez, 1998). This conclusion was confirmed by our study, in which soil clay and organic C decreased with an increase in erosion depth, by 59.6% and 71.2%, respectively, in the severely eroded sites compared to the non-eroded control sites. Regression analysis showed that there was an exponential decline in soil organic C (SOC) content with a loss of clay (v, %), described by the function: SOC content ðg kg 1 Þ ¼ 1:43540:6365 P < 0:0001; r 2 ¼ 0:97 Wezel et al. (2000) indicate that in arid and semiarid ecosystems, soil organic matter concentration is one of the most important factors influencing the storage of nutrients
Table 3 Pearson correlation among soil properties
Sand pH Org. C Total N Total P Total K Av. N Av. P Av. K Moist. Temp.
Clay
Sand
pH
Org. C
Total N
Total P
Total K
Av. N
Av. P
Av. K
Moist.
0.982*** 0.975*** 0.950** 0.928** 0.886** 0.935** 0.626 0.501 0.930** 0.890** 0.736
0.969*** 0.931** 0.914** 0.880** 0.950*** 0.619 0.552 0.878** 0.885** 0.711
0.983*** 0.972*** 0.958*** 0.931** 0.764* 0.525 0.945** 0.968*** 0.606
0.992*** 0.952*** 0.925** 0.752 0.608 0.968*** 0.966*** 0.620
0.952*** 0.937** 0.755* 0.644 0.965*** 0.970*** 0.613
0.879* 0.148 0.439 0.886* 0.982*** 0.402
0.595 0.665 0.871* 0.865 0.740
0.148 0.675 0.876* 0.029
0.566 0.450 0.652
0.925*** 0.675
0.434
*Correlation is significant at the 0.05 level; **significant at the 0.01 level; ***significant at the 0.001 level.
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and water in nutrient-poor sandy soils. In our study, soil nutrients and soil moisture decreased significantly with a reduction in organic C and clay content, with total N and available N decreasing by 67.4% and 64.5%, and total P and available P decreasing by 31.4% and 38.8%, respectively, and average soil moisture decreasing by 51.8%, in the severely eroded farmland compared to the Ctrl farmland. In particular, the lowest soil moisture content during the dry season was lower than the wilting point for local corn. This indicated that soil nutrient status and water-holding capacity worsened markedly after the loss of clay and soil organic C by long term wind erosion, which was evidently unfavorable for crop growth (Lal, 1998; Larney et al., 1998). Lowery et al. (1995) and Larney et al. (1998) had confirmed that the consequences of wind erosion include a reduction in crop production by selective removal of the finest soil particles with nutrients and organic matter, a reduction in soil water-holding capacity, and increased degradation of soil structure. Thus wind erosion has been considered one of the main limiting factors for plant productivity in some areas (Ettershank et al., 1978). Although sand accumulation also had a significant effect on particle size distribution, nutrient content and waterholding capacity, this effect was significantly less than that of wind erosion ( P < 0.05). For example, in the severe sandaccumulation sites, the content of clay, organic C, total N, total P and soil water decreased by 2.0%, 19.3%, 21.7%, 13.7% and 26.7%, respectively, compared with the Ctrl sites, while in the severely eroded sites the same factors decreased by 59.6%, 71.2%, 68.8%, 31.6% and 66.4%. It is evident that wind erosion can result in a loss of the finest soil particles and soil nutrients, and in degradation of soil structure (Lowery et al., 1995; Larney et al., 1998), but sand accumulation does not result in any loss of original soil clay particles or nutrients, only in a reduction of clay and nutrient concentration because of additional sand deposited in the soil. Moreover, the original cultivated surface layer can be destroyed by continual wind erosion, but this phenomenon does not occur in the sand-accumulation areas. These results are in agreement with observations by Su et al. (2002), Zhao et al. (2003), and Gomes et al. (2003).
5. Conclusion The research results showed that long-term wind erosion significantly changed some soil properties, including increased sand content and pH values, and decreased clay content, organic matter, nutrients, and soil water. These changes resulted in soil barrenness, dryness and coarseness, and caused deterioration of land resources. In particular, severe wind erosion not only resulted in a rapid decrease of soil nutrients and water-holding capacity, but also destroyed the surface soil layer and led to exposure of the sandy parent material to wind erosion, which could lead to more intense land degradation. Some sand-
accumulation sites showed a decrease in soil nutrient concentration and water content, but these decreases were significantly less than in wind-eroded sites. However, the effects of more severe sand accumulation on farmland soil need to be further studied.
Acknowledgements The authors are grateful to the anonymous reviewers for their critical review and comments on drafts of this manuscript. This research was funded as one of the Chinese National Fund Projects (40471004).
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