Catena 124 (2015) 68–76

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Rates of soil erosion in China: A study based on runoff plot data

Qiankun Guo, Yanfang Hao, Baoyuan Liu ⁎State Key Laboratory of Earth Surface Processes and Resources Ecology, School of Geography, Beijing Normal University, 100875, Beijing, China

⁎ Corresponding author at: State Key Laboratory oResources Ecology, School of Geography, Beijing Norma19, Haidian, 100875, Beijing, China. Tel.: +86 10 5880995

E-mail address: baoyuan@bnu.edu.cn (B. Liu).

http://dx.doi.org/10.1016/j.catena.2014.08.0130341-8162/© 2014 Elsevier B.V. All rights reserved.

a b s t r a c t

a r t i c l e i n f o

Article history:Received 17 December 2013Received in revised form 14 August 2014Accepted 18 August 2014Available online xxxx

Keywords:Runoff plotsSoil loss ratesLand useRunoffChina

Soil erosion has been a major environmental issue in China. However, the overall rate and the variability inrunoff and soil loss of different regions and land uses in China have not been reported in the literature. Inthis study, an extensive database of runoff plots in China was compiled. Runoff and soil loss rates of sheetand rill erosion under natural conditions based on plot studies, are reviewed. The history of plot studiesin China is briefly introduced, and basic information, such as the geographic distribution of soil erosionmonitoring sites, the distribution of slope length and the slope gradient of runoff plots, is described. Therunoff and soil loss rates of five water erosion regions in China were analyzed in terms of the main landuse types. The soil loss rate was 30.87–107.44 t ha−1 a−1 on fallow land and 7.65–49.38 t ha−1 a−1 on farm-land under conventional tillage. The land use types with permanent cover experienced the lowest soil lossrates, which were 0–1.89, 0.28–8.06 and 3.98–1.57 t ha−1 a−1 for forest, shrub and grassland, respectively.In China, the regional differences in the soil loss rate were mainly observed on fallow land and farmland,whereas almost no differences were observed on forest, shrub and grasslands. The soil loss rates of forest,shrub and grasslands showed no significant differences worldwide. However, the soil loss rates of farmlandwith conventional tillage in northwest and southwest China were much higher than in most other coun-tries. This indicated that farmlands in China are still suffering from a very serious erosion problem thatrequires additional future attention. This study provided a broad assessment of sheet and rill erosion for pri-oritizing problems and selecting the appropriate erosion control practices.

© 2014 Elsevier B.V. All rights reserved.

1. Introduction

Soil erosion causes significant problems, both on-site and off-site.The on-site effects include a loss of productivity from a shift in soiltexture and breakdown of soil structure resulting from loss of finesand organic matter, among other problems. The off-site problemsarise from sedimentation downstream, which reduces the capacityof rivers and drainage ditches, enhances the risk of flooding andshortens the design life of reservoirs. Such sediment problems resultin huge economic costs (Morgan, 2005). Therefore, the protection ofsoil resources has been identified as an important objective of envi-ronmental policy (CEC, 2006). This requires a correct assessment oferosion rates and their distribution (Cerdan et al., 2010). In theUnited States, this assessment has been conducted as a national ero-sion inventory (Holeman, 1981), which was part of national resourcesinventory (NRI) (Nusser and Goebel, 1997). NRI was conducted since1977 and much valuable data was acquired. The soil loss rates were

f Earth Surface Processes andl University, Xinjiekou Wai St.9.

calculated by USLE and RUSLE, which were developed on the basisof field plot data. Satellite remote sensing was also widely used duringthe past 30 years for regional-scale water erosion assessments. How-ever, the main concern with this methodology is the lack of validationdata or ground truthing (Vrieling, 2006). Field measured data are nec-essary to support the interpretation and model calculation of an ero-sion assessment. The USLE-type runoff plots seem to be the onlystandard method for field measurements because this quantificationtechnique enables the comparison of results from different areasand different studies (Visser et al., 2004).

Extensive assessments of soil loss over large areas were conduct-ed in different nations or continents by adopting field-measured datafrom runoff plots. The United States has collected soil erosion dataover a long period of time and has used a standardized methodologyto analyze the data, which led to the development of the UniversalSoil Loss Equation (Wischmeier and Smith, 1965, 1978) and the Re-vised Universal Soil Loss Equation (Renard et al., 1997). These twoequations are used worldwide. Various erosion assessment modelshave also been developed for Europe (Goblin et al., 2004; Kirkbyet al., 2008). Soil loss rates were reported in Europe (Cerdan et al.,2010), Africa (Stocking, 1984; Roose, 1976) and Australia (Lu et al.,2003). These data provided a basic magnitude of soil erosion for

69Q. Guo et al. / Catena 124 (2015) 68–76

different countries or continents. However, few data were reportedfrom China. This information could be used as a reference for a na-tional soil conservation strategy.

Over the last 80 years, numerous experimental studies of runoff andsoil loss have been conducted in China using runoff plots. Despite theconsiderable differences in plot size, conservation measures and lengthof the measurement period, the runoff plot data provided valuable in-formation about runoff and soil loss rates in China. Various local erosionassessment models have been developed in China from these data(Zhang et al., 1992; Zhou et al., 1995; Lin et al., 1997; Wu et al., 1998;Yang, 2002; Bi et al., 2006). However, few studies were conductedthat comprehensively and quantitatively explored the national scale ofsoil erosion.

Consequently, a large dataset of runoff and soil loss rates measuredon runoff plots under natural rainfall conditions across the countrywas compiled, and this database was used to provide a comprehensiveassessment of both runoff and soil loss rates measured at the plot scale.The specific objectives of this paper are as follows: 1) to briefly intro-duce the history of plot studies in China; 2) to develop a database ofsoil erosion under various land use types in different erosion regions;and 3) to assess the variability of both runoff and soil loss rates ofsheet and rill erosion among regions, land uses and soils. The soil lossrates obtained in this study will be compared with other regions ofthe world and used to provide an important reference for furthererosion studies and the application of erosion control programs at aregional scale.

Table 1Data sources used for the database compilation.

Region Provinces Reference

Northeast Heilongjiang Chen et al., 2006; Zhao and Wei, 2009; Nenjiang;InnerMongolia

Chen et al., 2006; Central experimental station of soiland water conservation in Hulunbuir, 1994;

Jilin Chen et al., 2006; Han et al., 2007;North Liaoning Chen et al., 2006; Han et al., 2007; Lin et al., 1997; Sun

et al., 1997;Beijing Miyun, Fangshan, Huairou, Mentougou and Yanqing;Hebei Gu et al., 1994; Lv et al., 1999; Wang and Xie, 1999;Henan Huang et al., 2000;Shandong Han and Guo, 1991; Liu et al., 2007;Jiangsu Zhang et al., 2009;

Northwest InnerMongolia

Zhungeer banner (Personnel communication);

Shaanxi Hou and Cao, 1990; Lu et al., 1988; Soil and waterconservation committee in the middle reach of YellowRiver, 1965; Zhang and Lu, 1993;

Gansu He et al., 1992; Soil and water conservation committeein the middle reach of Yellow River, 1965;

Henan Li et al., 1992;Qinghai Xu et al., 2007; Zhu et al., 2008a;

Southwest Hubei Gao et al., 2004; Huang et al., 1998; Xiang et al., 2001;Yong, 2011; Zheng and Zhang, 2006;

Hunan Liu and Tan, 1992; Zhang and Zhong, 1999; Zhou et al.,2009, 2010;

Sichuan Chen et al., 2002, 2009; Li et al., 2005; Lin et al., 2007a,b; Lv et al., 2000; Soil and water conservationcommittee of Sichuan Province, 1991; Wu et al., 2007;

Chongqing Jiang et al., 2011; Li and Li, 1991;Guizhou Zhang et al., 2000, 2001a; Zhu et al., 2008b;Yunnan Mi et al., 2006; Wang et al., 1982; Yang, 1999;

South Zhejiang Jin and Wang, 2000; Li and Zhang, 2000; Yang et al.,2004; Yuan et al., 2001;

Jiangxi Fan et al., 2005; He, 1995; Liu, 2006; Liu and Cheng,2003; Wang et al., 2008; Xie et al., 2004; Zhang et al.,2001b; Zuo et al., 2003;

Fujian Chen, 1999, 2006; Ding et al., 2006; Huang et al., 2007;Lin et al., 1998; Zhou et al., 1995; Zhu et al., 2003;

Guangdong Chen and Wang, 1992; Liu et al., 2000;Guangxi Huang et al., 2010, 2012; Huang and Liang, 1999;Hainan Yi et al., 2004;

* Field data of “Nenjiang, Miyun, Fangshan, Huairou, Mentougou and Yanqing” were mea-sured by the soil conservation research group at Beijing Normal University (BNU).

2. Materials and methods

2.1. Plot database: selection criteria and compilation

The database was mainly compiled from Soil Conservation Stationbulletins, journal papers and PhD dissertations (Table 1). Three soil ero-sion regions in China were divided according to the dominant erosiveagents:water erosion region, wind erosion region and frozen-thaw ero-sion region. For water erosion, five water erosion regions wereestablished for China: the northeast (NE) black soil region; the northern(N) rocky and earth mountain region; the northwest (NW) LoessPlateau region; the southwest (SW) purple soil region; and the south-ern (S) red soil hilly region. The five regions were decided by synthesisanalysis of factors affecting soil erosion, such as soil types, topography,climate, and so on. They are widely used in China for soil erosionresearch, soil erosion inventory and soil conservation planning.

Plot data were selected according to the following criteria: (i) onlydata obtained from direct measurements were selected, (ii) only datawith clear site, management, and plot-data descriptions for interpreta-tion were selected. The data recorded for analysis included the plotlength and slope gradient, the measurement period, and the land useand conservation measures. If a site's data base was not sufficiently de-tailed, the plot data were excluded from the database. Fallow land wasincluded in the database because this type of land has often been usedin soil erosion studies as a reference, representing maximum soil loss;however, this was not a common land management practice. Plotsunder conservationmanagementwere also included in the database be-cause this was a widely used land use practice, especially on farmland.

Every record corresponded to a unique combination of land use, plotlength, slope gradient, conservation measure and measurement period.For each plot, the runoff and soil loss rate for each year were recorded.However, some studies did not present values of runoff and soil lossrates for each year but reported themean or total data for themeasure-ment period. In this case, themean runoff and soil loss rate were count-ed as one record for each plot. Most records of runoff and soil loss rateswere reported annually, and few of them were averaged over severalyears.

A total of 2823 plot-year data were collected for analysis from 73different sites, which were widely distributed in China (Fig. 1). Thisdatabase for China is currently one of the largest compilations of runoffand soil loss rates on a plot scale. The statistics for the compiled datafrom the five different regions are shown in Table 2.

The earliest record in this database is from 1945 in Tianshui, GansuProvince. The number of plot years increased in the 1950s, declined inthe 1960s to the point that no data was collected during much of the1970s. The number of plot years boomed in the next decade, reachinga peak of 144 plot years in the late 1980s. The number of plot-years sub-sequently started to slightly decline, which is possibly attributed to thefact that some ongoing research has not yet been reported (Fig. 2).

The data used in this study varied in terms of slope gradient, slopelength and land use. Six land use types were classified, includingfallow (no vegetation), farmland, forest, shrub, grassland and orchard.The slope length of the plots ranged from 0 to 300 m. However, onlythe plots with slope length of more than 5 m were used in the studybecause plots with length less than 5 m were considered to be notrepresentative. Most of the data were collected from plots between5–40 m lengths with a peak in plot years at the length of 10–20 m.The slope gradient varied from 0° to 40°, with a peak in plot years ata slope gradient of 10° to 20°. For all of the land use types, the largestnumbers of plot-years were on 10–20 m long slopes and the secondand third largest number of plot-years were on 5–10 m long slopesand 20–40 m long slopes (Fig. 3). Very few plots were constructedon slopes less than 5 m or longer than 40 m, and these plots weremainly used for quantifying the slope length factor. A frequency dis-tribution of the slope length for all of the land use types revealed asimilar trend. For the slope gradient, the largest number of plot-

Fig. 1. Geographic distribution of soil erosion monitoring sites used in this study.

70 Q. Guo et al. / Catena 124 (2015) 68–76

years was on a slope of 10°–20° for all of the land use types. The sec-ond and third largest numbers of plot-years for the different landuse types were not the same. The second largest number of plot-years for farmland was on a slope of 5°–10°, while for forest/shrub/grass (perennial vegetation), they were on a slope of 20°–30°(Fig. 3). The distribution of slope gradient provided a reference ofthe natural field conditions. Farmlands in natural field conditions areusually on the gentle slopes, while forests are generally situated onsteeper slopes. This was in accordance with the slope gradient distri-bution of runoff plots, as the slope gradient for farmlands was lower,while the slope gradient was higher for forest/shrub/grass.

2.2. Data analysis

The objective of this paper was to analyze the magnitude and vari-ability of runoff and soil loss of sheet and rill erosion in China and tocompare these rates with those in other countries. There is a high de-gree of variability of measured runoff and soil loss rates from site tosite due to different soil types, rainfall conditions, topography, landuse types, conservation measures and other factors. Therefore, severalgroups were generated for analysis in this study according to the differ-ent regions and land use types. Five water erosion regions and six landuse types were classified, as previously mentioned.

The measuring period is also an important factor that contributes tothe variability of runoff and soil loss rates. The data that were acquired

Table 2Database statistics for each water erosion region.

Erosion region No. of sites Plot-year Plot-year

Mean Median Maximum Minimum

Northeast 7 238 4.1 4 15 1North 12 674 6.4 7 17 1Northwest 9 764 4.8 4 12 1Southwest 25 568 3.3 3 12 1South 20 579 3.5 3 10 1Total 73 2823 4.3 4 17 1

during a long measurement period were more reliable because theycaptured more of the natural variability. According to the central limittheorem, the standard error of a sample is inversely related to thesquare root of the number of observations (Tijms, 2004). Therefore,the square root of the number of plot-years was used as a weightingfactor for runoff and soil loss rate calculations according to Eq. (1):

Arlc ¼Xm

i¼1

Arlciffiffiffiffiffiffiffiffinrlci

pð Þ=Xm

i¼1

ffiffiffiffiffiffiffiffinrlci

p ð1Þ

where Arlc is the runoff or soil loss rate of plots with conservation mea-sure c and land use lwithin region r. Arlci is the average runoff or soil lossrate for plot i and nrlci is the number of plot years for plot i.

Fig. 2. Time distribution of the number of plot-years since 1945.

Fig. 3. Distribution of the number of plot-years of different land use types over the slopelength and slope gradient.

71Q. Guo et al. / Catena 124 (2015) 68–76

3. Results and discussions

3.1. History of plot research in China

Miller (1926) constructed the first runoff plots in 1917 in Missouri,USA, whereas, field measurements in China started as early as 1922.With the help of the American scientist W. C. Lowdermilk, runoff plotswere constructed in Qinyuan and Ningwu, Shanxi Province and Qing-dao, Shandong Province to measure the effects of forest vegetation onsoil loss (Guo and Li, 2009). However, no record of these field measure-ment datawere preserved. Available soil loss data recordswere initiated

Fig. 4. Geographic distribution of soil erosion monitoring site

at the Tianshui experimental station in 1945, in Gansu Province, whichwas again constructedwith the help ofW. C. Lowdermilk. Xifeng stationin Gansu Province and Suide station in Shaanxi Province were built in1951 and 1952, respectively. However, measurement stagnated duringthe Cultural Revolution from 1966 to 1976, and very little experimentaldata were measured during this period. The research boomed after1980, and subsequently, more runoff plots were constructed and morefield measurements were conducted. There are in total 129 sites of run-off plots presented in the literature. However, detailed information ofsome runoff plots were not reported, and therefore, the plots of thesesites were not included in this study. In 2000, after 20 years of fieldmeasurement at a local scale, the need for assessing soil loss on a nation-al scale arose. To meet this need, the Monitoring Center of Soil andWater Conservation, in theMinistry ofWater Resources, initiated a Chi-nese monitoring network and information system project for soil andwater conservation. The project aimed at constructing 738 soil erosionmonitoring sites, including water erosion, wind erosion and freeze-thaw erosion. Among these sites, 356 monitoring sites were deployedwith runoff plots. The project was divided into two stages. The firststage began in 2002 and finished in 2007, with the construction of163 monitoring sites with runoff plots. The second stage started in2007, and the runoff plots for the remaining 193 monitoring sites arestill under construction (Fig. 4).

3.2. Runoff and soil loss rates

Themean values and standard deviations of long term rainfall, slopelength, slope gradient, and runoff and soil loss rates under various landuse types are shown in Table 4. These data provide quantitative infor-mation about runoff and soil loss in China.

To understand the general concept and make it easier to comparesoil loss rates, five intensity groups were defined based on soil loss tol-erance (T): b T; 1–2 T; 2–4 T; 4–8 T and N 8 T according to USLE(Wischmeier and Smith, 1965). The T value ranged from 2.24 to

s in the Soil Conservation Monitoring Network Project.

Table 3Soil loss rates for the main land use types of different continents.

Continent (nation) Land use types Details of land use Soil loss Range of soil loss SD Source

t ha–1 a–1 Intensity group t ha–1 a–1

Australia Fallow Bare soil 84.60 4 6.2–276 Lu et al., 2003Europe Fallow Fallow 17.12 2 30.23 Cerdan et al., 2010Europe Fallow Fallow 12.80 2 24.32 Maetens et al., 2012Africa Fallow Fallow 109.56 5 10.8–146 Stocking, 1984USA Fallow Fallow 57.16 4 USDA-WEPPAustralia Farmland Farmland 11.00 1 0.02–100.5 Lu et al., 2003Europe Farmland Farmland 6.33 1 13.46 Cerdan et al., 2010Europe Farmland Farmland 6.50 1 18.20 Maetens et al., 2012West Africa Farmland Farmland 14.90 2 2.8–42.5 Roose, 1976USA Farmland Farmland 18.37 2 0.33–95.15 USDA-WEPPAustralia Forest/Shrub Woodlands (forest, scrub) 1.85 1 0–5.2 Lu et al., 2003Europe Forest Forest 0.00 1 0.00 Cerdan et al., 2010Europe Forest Forest 0.70 1 3.64 Maetens et al., 2012West Africa Forest Natural environmental 0.05 1 0.01–0.6 Roose, 1976Africa Grass 10 year grass 0.70 1 Stocking, 1984Australia Grass Grazing lands 2.52 1 0.07–14.5 Lu et al., 2003Australia Grass Pasture (no/light grazing) 0.27 1 0.005–0.8 Lu et al., 2003Europe Grass Grass 0.29 1 1.15 Cerdan et al., 2010Europe Grass Grass 0.70 1 1.40 Maetens et al., 2012Europe Grass Rangeland 0.70 1 1.54 Maetens et al., 2012USA grass Grass 0.34 1 0.01–1.01 USDA-WEPPAfrica Shrub Natural bush 0.60 1 Stocking, 1984Europe Shrub Shrub 0.13 1 0.19 Cerdan et al., 2010Europe Shrub Shrub 0.60 1 1.20 Maetens et al., 2012West Africa Forest Burned 0.19 1 0.15–0.26 Roose, 1976Europe Forest Post-fire 1.50 1 3.15 Maetens et al., 2012Europe Orchard Vineyard 23.64 3 26.00 Cerdan et al., 2010Europe Orchard Orchards 20.60 2 19.40 Cerdan et al., 2010Europe Orchard Tree crops 13.40 2 18.76 Maetens et al., 2012Europe Orchard Vineyard 17.90 2 73.39 Maetens et al., 2012

*USDA-WEPP: plot data were acquired from: http://www.ars.usda.gov/Research/docs.htm?docid=18569.

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11.21 t ha−1 a−1, and the highest value was used to define the groups.World-wide research results are also presented in Table 3.

3.2.1. Fallow landFallow land plots were constructed for soil erodibility calculations

and were also used as the basis for the comparison of soil loss betweenland uses. A total of 290 plot-years of fallow land were used in thisstudy. In terms of the five intensity groups, the soil loss rates for fallowplots were in group 3 for the northeastern and northern regions, group4 for the northwestern region and group 5 for the southwestern andsouthern regions (Table 4). This finding was mainly due to the com-bined effects of slope gradient and rainfall. The slope gradient in thenortheastern and northern region was the lowest, whereas it wasmuch steeper in the northwest. The higher intensity rainfall in southernChina contributed to higher soil loss rates in the southern and south-western region, especially the latter, which also had the steepest slopeof the five regions.

Compared with other countries (continents), the soil loss rate inEurope was the lowest and was classified as intensity group 2;Australia and the USA were classified as group 4, and Africa was ingroup 5 (Table 3). Therefore, the northwestern region of China experi-enced the same level of soil loss on fallow land as Australia and theUSA in group 4. China's southern and southwestern regions shared thehighest level of soil erosion and were in the same group (group 5) asAfrica. The soil loss rates in the northeastern and northern regionswere the lowest in China. However, they were still in a higher groupthan Europe, which was the lowest group of different continents. Acomparison of soil loss rates of different continents determined thatChina had some of the highest soil loss rates on fallow land.

The results for southern China (the southwestern and southernregions) were similar to other studies (Table 4). Thongmee andVannaprasert (1990) reported that the runoff and soil loss rate in

Thailand, near southern China, were 378 mm and 74.2 t ha–1 a–1. Hilland Peart (1998) concluded that the runoff and mean soil loss rates insouthern China were 462 mm and 153.03 t ha–1 a–1.

3.2.2. FarmlandPlots of farmland covered 1421 plot-years in the database and were

50.3% of the total 2821 plot-years. This indicated that soil loss on farm-land garnered more attention in China than any other land use. Landmanagement and conservation practices on these plots included con-ventional tillage (CT), ridge tillage (RT), terracing (TR), ridge tillagewith barriers in the furrow (RTBF), hedgerow planting (HP), grass-crop rotation (GC) and no till (NT). Farmlands with CT, RT and TRwere widely distributed in China, and the plot-years of CT, RT and TRin this study were 621, 492 and 138, respectively. This accounted for88.0% of the 1421 plot-year totals (Table 4).

For conventional tillage, the soil loss rate in the southern regionwas the lowest nationally and in intensity in group 1, which indicat-ed that the soil loss rate was less than the highest T value. The lowsoil loss was most likely due to the extensive crop cover in the south-ern region. Runoff in the southern region was not the lowest nation-ally. In contrast, runoff was the lowest in the NW region but the soilloss was the highest under CT, despite this region having the greatestslope gradient. The high soil loss with low runoff was likely a reflec-tion of the characteristics of loess soil under CT, such as low organicmatter, weak soil structure and high erodibility. The soil loss rates inthe northeastern and northern regions were in group 2, most likelydue to the relatively lower slope gradient and the lower rainfall in-tensity compared with the soil loss rates in the northwestern andsouthwestern regions. The soil loss rate in the southwest was ingroup 3 because its crop cover was not as effective as in the southernregion. The slope gradient and rainfall were higher in the southwest-ern region than in the northeastern and northern regions (Table 4).

Table 4Runoff and soil loss rates for various land use types in five water erosion regions of China.

Land use Region Plot- year Conservation Measure Rainfall (mm) Slope gradient(°)

Slope length(m)

Runoff (mm) Soil loss (t ha−1 a−1)

Mean SD Mean SD Mean SD Mean SD Mean SD Group

Fallow NE 22 570 89.1 6.1 1.1 21.8 5.5 48.75 8.61 43.59 15.39 2N 131 574 114.6 13.5 2.8 16.6 6.6 67.42 17.62 30.87 27.65 3NW 45 445 72.0 16.2 10.0 15.6 9.9 47.60 13.86 53.16 23.32 3SW 15 1229 332.9 20.7 7.9 19.4 6.3 268.26 141.33 107.44 66.53 4S 77 1551 137.6 14.7 5.4 23.3 12.2 367.26 273.39 98.04 55.76 4

Farmland NE 106 Conventional 522 60.8 4.5 2.7 46.1 73.4 39.28 14.83 13.40 10.71 1N 110 Conventional 632 132.7 11.2 4.8 15.6 6.1 62.55 29.07 17.27 16.38 2NW 244 Conventional 515 94.2 21.5 7.1 19.8 9.4 27.71 12.71 49.38 57.61 4SW 129 Conventional 1094 206.6 14.8 6.2 16.4 6.0 145.17 62.67 35.44 27.64 3S 32 Conventional 1490 102.3 15.8 6.0 19.2 1.3 61.61 11.38 7.65 6.80 1NE 62 Ridge tillage 519 73.4 6.8 1.6 21.0 4.4 12.88 15.15 3.56 2.78 1N 35 Ridge tillage 686 107.7 10.4 3.8 20.6 5.0 - - 7.84 12.86 2NW 186 Ridge tillage 584 95.9 12.7 6.2 18.7 4.6 16.66 8.50 19.27 13.35 2SW 158 Ridge tillage 1018 135.3 16.0 7.3 14.0 4.9 84.05 57.16 24.31 40.15 3S 13 Ridge tillage 1400 0.0 15.0 0.0 20.0 0.0 23.89 5.37 1.57 0.91 1NE 4 Terracing 515 - - - 30.0 - 0.00 0.00 0.00 0.00 1N 34 Terracing 741 162.2 6.9 3.0 15.3 5.8 16.56 19.64 1.19 0.65 1NW 16 Terracing 504 69.1 8.4 1.6 33.8 9.6 1.03 2.35 0.12 0.28 1SW 22 Terracing 1211 285.4 15.9 5.0 18.6 4.2 64.45 45.27 6.03 4.26 1S 62 Terracing 1585 46.8 17.3 7.0 18.0 1.0 - - 0.59 0.69 1

Forest NE 4 515 - 11.0 - 30.0 - 0.00 0.00 0.00 0.00 1N 20 718 161.3 13.6 5.6 18.0 5.2 18.51 12.29 1.14 0.68 1NW 43 465 47.9 25.9 5.6 21.1 3.1 0.67 0.82 0.10 0.12 1SW 61 1407 217.5 21.6 8.3 18.2 3.6 35.84 49.48 0.38 0.86 1S 90 1544 157.8 23.4 7.7 20.1 5.7 75.25 109.25 1.89 4.43 1

Grass NE 11 553 107.0 6.5 1.3 23.6 5.5 26.30 7.97 3.98 5.16 1N 33 743 143.6 14.2 4.8 18.8 4.4 41.72 44.17 5.78 9.28 1NW 82 497 56.7 30.7 5.0 26.4 10.9 34.43 58.97 11.57 12.72 2SW 29 1189 332.7 15.8 7.3 16.8 4.2 58.23 67.68 5.48 4.15 1S 36 1636 123.1 17.4 3.6 15.4 7.6 296.23 317.23 8.30 11.06 1

Shrub NE 6 595 117.0 6.7 0.6 30.0 0.0 - - 6.52 1.28 1N 151 562 104.2 18.0 6.3 11.2 6.3 12.38 12.13 1.39 5.95 1NW 70 515 44.8 29.2 4.1 29.0 10.0 19.98 30.75 8.06 7.47 1SW 53 1105 289.3 23.6 4.7 16.9 2.9 54.97 69.42 6.12 9.17 1S 20 1565 415.6 20.5 10.9 17.5 5.4 61.36 61.21 0.28 0.31 1

Orchard N 68 Horizon stage 631 76.3 15.2 3.5 10.0 0.0 17.41 12.21 5.30 5.90 1N 2 Terracing 524 - 12.0 - 30.0 - - - 0.16 2.12 1N 13 Tree pan 497 19.1 13.4 1.7 14.6 5.8 19.23 13.74 7.85 8.75 1S 18 Full grass Cover 1537 144.4 15.5 5.0 21.7 2.7 27.78 15.17 0.06 0.06 1S 27 Strip grass cover 1580 127.4 16.5 5.2 21.5 3.3 111.50 246.63 0.81 2.30 1S 15 Ridge tillage 1435 48.8 14.0 2.1 23.3 3.5 55.43 77.07 4.47 8.93 1S 42 Terracing 1502 112.9 14.8 4.7 20.7 1.9 56.54 50.46 5.32 7.46 1S 2 Hedgerow 1517 - 29.0 - 20.0 - 135.86 12.39 5.92 5.12 1S 17 Conventional 1570 158.5 13.5 2.4 22.5 4.3 190.56 524.02 7.43 10.28 1S 25 No grass cover 1544 128.5 13.3 8.6 33.0 17.1 349.38 374.51 36.01 39.72 3S* 4 Full grass cover 1554 160.9 15.3 5.5 22.5 2.9 226.09 125.62 13.84 8.90 1S* 3 No grass cover 1522 180.7 15.7 6.7 21.7 2.9 271.33 178.66 112.74 17.88 2S* 6 Strip grass cover 1578 130.9 16.4 5.4 22.5 2.7 227.59 73.52 29.96 13.16 2S* 5 Terracing 1449 183.5 11.6 2.2 22.0 2.7 123.45 61.87 10.86 7.38 1

S* represented the orchard for the first 1–3 years, in Southern China.

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World-wide (Table 3), the soil loss rate in the southern region was inthe same group (group 1) as the rates in Europe and Australia. Soilloss rates in the northeastern and northern regions were both ingroup 2, which was the same level as the rates in west Africa andthe USA. The soil loss rates in western China (the southwestern andnorthwestern regions) were the highest worldwide, which impliedthat land management practices should be undertaken to reducethe soil loss rate.

Ridge tillage was the most widely used tillage method forprotecting soil on farmland slopes. The soil loss rates in the south-western and northwestern regions were highest nationwide andbelonged to group 3 and group 2, respectively. For the SW, this resultwas mainly attributed to the steeper slope gradient, which resultedin the highest runoff rates nationally. This was not the case for theNW region, which had a moderate runoff and slope gradient but dis-proportionately high soil loss. The soil loss rates in other regions

were classified in group 1, which was less than the highest T value.This meant that ridge tillage could control soil loss in the NE, N andS effectively. Ridge tillage did substantially reduce soil loss in theSW and NW regions compared to CT.

The benefits of terracing for soil and water conservation were themost impressive of the conservation measures. Runoff was reduced by55 to 100% and soil loss was reduced to less than 6 t ha–1 across all re-gions. Excluding the southwestern region, soil loss rates were lowerthan the lowest T value (2.242 t ha–1), which meant that the soil lossrate on farmland was effectively controlled by terracing.

The remaining 170 plot-years of farmland plots were managedunder four conservation practices: ridge tillage with barriers in the fur-row (RTBF); hedgerow planting (HP); grass-crop rotation (GC) and notill (NT). HP was observed in all regions, except the NW. Soil loss ratesfor HP were less than the lowest T value, with the exception of thesouthwestern region. Other practices were only reported in one or

Fig. 5. Comparison of rainfall, runoff and soil loss of five water erosion regions for all landuses.

Table 5Soil loss rates for arable lands under RTBF, HP, NT and GC.

Conservation measures Region Rainfall (mm) Plot-year Slope gradient (°) Slope length (m) Runoff (mm) Soil loss (t ha–1 a–1)

Ridge tillage with barrier in furrow (RTBF) NE 455 4 5.0 20 17.50 1.96NW 476 6 21.8 15 3.80 3.77

Hedgerow planting (HP) NE 595 6 6.7 30 - 1.97N 524 2 12 30 - 0.96SW 1005 52 16.3 21 55.38 6.59S 1400 10 15.0 20 35.30 1.25

No till (NT) NE 495 7 5.0 20 25.84 1.74N 631 16 6.5 11 51.28 2.00

Grass-crop rotation (GC) NW 542 67 15.3 21 11.83 15.21

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two regions, indicating that thesemeasures were not widely adopted inChina. Among these practices, only GC and PC in the northwest had soilloss rates higher than the lowest T value (Table 5).

3.2.3. Forest, shrub and grasslandThe runoff and soil loss rates of forests, shrubs and grasslandswill be

discussed together. In the Loess Plateau (NW), these land use practicesare applied to the steepest slopes to control erosion. Therefore, the NWhad the greatest slope gradients for these land uses. However, the NWdid not have the greatest runoff, which was instead observed in theSW region for all three land uses. In fact, forest in the NWwas highly ef-fective for controlling runoff on steep slopes, with only 0.7mmof runoffobserved. As a result, soil loss was minimal under forests despite soilloss being disproportionately high in the NW for other land uses. Thesoil loss rates of forests ranged from 0 to 1.89 t ha–1 a–1 in all of the re-gions (Table 4), which indicated that theywere all less than the lowest Tvalue (2.242 t ha–1). These results were the same as the worldwide re-sults (Table 3).

The soil loss rates for shrubs were in group 1 for all of the regions(Table 4). Two of the regions (north and south regions) had soil lossrates that were less than the lowest T value (2.242 t ha–1), whichwere the same as the worldwide results (Table 3). The other three re-gions experienced rates 3 to 4 times higher than the lowest T value,which was larger than rates observed in other countries. The highestsoil loss rate for shrubs was in the NW (loess) region, despite havingthe second lowest runoff. The soil loss for NW, NE and SW regionswas higher than rates observed worldwide and was likely due to graz-ing or human harvest for fuel. This finding suggests that the shrubs inChina should be protected for ecological restoration.

As observed for shrubs, the soil loss rate for grasslandwas highest intheNW(loess) region, despite having the second lowest runoff. Soil lossrates for all grassland regions were higher than the lowest T value,whereas the rate in NW was even higher than the highest T value(Table 4). However, all of the values acquired from worldwide studieswere less than the lowest T value, except for grazing lands inAustralia, which were slightly higher than the lowest T value(Table 3). The results suggested that soil losses from grasslands inChina were larger than other countries. This is likely due to overgrazing,suggesting the need to reduce animal numbers to match the grasslandcarrying capacity.

Although only a small number of plot-years in southern China(SW and S) were measured in post-fire plots, the results also clearlyindicated that the disturbance of permanent vegetation by fire led toa measurable increase in runoff and the soil loss rate. Runoff rangedfrom 124.2 to 300.7 mm and the soil loss rate ranged from 8.35 to34.64 t ha–1 a–1 following fires. This indicated the importance ofmaintaining vegetation. The soil loss rates of shifting cultivation inthe tropical regions of the Hainan province and Yunnan provinceranged from 5.4 to 48.9 t ha–1 a–1 (Hill and Peart, 1998), which hadthe same magnitude as southern China. However, the soil loss ratesof post-fire areas in Europe and Africa were much lower than insouthern China, which was most likely due to the heavy precipita-tion that occurs in southern (S and SW) China.

3.2.4. OrchardOrchards are widely distributed in the hilly areas of China, and the

plots of orchards were recorded in the N and S regions. These plots pro-vided a comprehensive overview of runoff and erosion under differentconservation measure treatments. Runoff and soil loss rates varied sub-stantially with different conservation practices. Runoff ranged from17.4 mm under conservation measures in the N region to 349.4 mm inthe S region, which had no cover. This result indicated that engineeringmeasures (terracing, tree pan and horizon stage), grass cover and tillagewere all effective in reducing runoff in orchard plots. Even CT can reduceapproximately 50% of runoff. Soil loss rates were less than the highest Tvalue for plots under conservation land management practices. Plotswith grass cover (full grass cover and strip grass cover) and terracingexperienced soil loss rates that were even lower than the lowest Tvalue (Table 4). However, the soil loss rate of orchard plots with nograss cover was much higher than the highest T value. Worldwide soilloss rates for orchards were only reported in Europe, which also hadrates that were higher than the highest T value. The runoff and soilloss rates were both higher than that of any other land use types,apart from fallow land, for orchards during the first 1–3 years. Thiswasmost likely due to the lack of vegetation cover. The results indicatedthat for orchards, soil conservationmeasures should be planned and im-plemented carefully.

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4. Conclusion

Rainfall, runoff and soil loss rates of each region were calculated asthe average value of different land uses in each region and are presentedin Fig. 5. This information provided an intuitive comparison of rainfall,runoff and soil loss rates between different erosion regions. Generally,rainfall and runoff in north China (NE, N and NW) was less than insouth China (SW and S) and NW had the lowest rainfall and runoff.However, soil loss rates in NW (Loess Plateau) were on the same levelas in south China (SW and S) and were much higher than in NE andN. Obviously, the NW region experienced small water discharges witha huge sediment load.

A review of runoff plot studies was performed for China, and themeasured runoff and sheet and rill erosion of various land use typeswere compiled. The analysis of the compiled runoff and sheet erosiondata for various land use types revealed the following conclusions.Field measurement started in 1922 and data from 1945 to the presentwere compiled into a comprehensive database. A new soil erosionmonitoring network project was started in 2002 with the constructionof 163 runoff plot sites until 2007, and 193 sites are still underconstruction.

The soil loss rates on fallow land in China were different from regionto region. The lower regions (NE, N and NW) were the same as in theUSA, while the higher regions (SW and S) were the same as in Africa.Soil loss for farmland and orchards under conventional tillage exceededthe soil loss tolerance. However, soil conservation measures, such asridge tillage and terracing, effectively controlled soil erosion.

Soil loss in forest was as low, or lower, as worldwide values for allregions. Soil loss in shrub and grassland was higher than world-widevalues, mainly due to overgrazing or fuel harvesting.

The high soil loss with low runoff in NW (Loess Plateau)was likely areflection of the characteristics of loess soils, such as low organicmatter,weak soil structure, high erodibility, and so on.

Acknowledgements

This study was funded by the National Basic Research Program ofChina (2011CB403304) and the Fund for Creative Research Groups ofNational Natural Science Foundation of China (No. 41321001).

Appendix A. Supplementary data

Supplementary data associated with this article can be found in theonline version, at http://dx.doi.org/10.1016/j.catena.2014.08.013.These data include Google maps of the most important areas describedin this article.

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