Effects of vegetation restoration on soil organic carbon sequestration at multiple scales in semi-arid Loess Plateau,China

Soil organic carbon (SOC) sequestration by vegetation restoration is the theme of much current research. Since 1999, the program of “Grain for Green”has been implemented in the semi-arid Loess Plateau, China. Its scope represents the largest vegetation restoration activity in China. However, it is still unclear for the SOC sequestration effects of vegetation cover change or natural succession promoted by the revegetation efforts at different scales under the semi-arid conditions. In this study, the changes in SOC stocks due to the vegetation restoration in the middle of Loess Plateau were estimated at patch, hill slope transect and small watershed scale from 1998 to 2006. Soil samples were taken from field for the determination of cesium-137 (¹³⁷Cs) and SOC contents. Vegetation cover change from 1998 to 2006 at the small watershed scale was assessed using Geographic Information System. The results showed that cropland transforming to grassland or shrubland significantly increased SOC at patch scale. Immature woodland, however, has no significant effect. When vegetation cover has no transformation for mature woodland (25 years old), SOC has no significant increase implying that SOC has come to a stable level. At hill slope scale, three typical vegetation cover patterns showed different SOC sequestration effects of 8.6%, 24.6%, and 21.4% from 1998 to 2006, and these SOC increases mainly resulted from revegetation. At the small watershed scale, SOC stocks increased by 19% in the surface soil layer at 0–20 cm soil depth from 1998 to 2006, which was equivalent to an average SOC sequestration rate of 19.92 t C y^− 1 km^− 2. Meanwhile, SOC contents showed a significant positive correlation (P < 0.001) with the ¹³⁷Cs inventory at every soil depth interval. This implied significant negative impacts of soil erosion on SOC sequestration. The results have demonstrated general positive effects of vegetation restoration on SOC sequestration at multiple scales. However, soil erosion under rugged topography modified the spatial distribution of the SOC sequestration effects. Therefore, vegetation restoration was proved to be a significant carbon sink, whereas, erosion could be a carbon source in high erosion sensitive regions. This research can contribute to the performance assessment of ecological rehabilitation projects such as “Grain to Green” and the scientific understanding of the impacts of vegetation restoration and soil erosion on soil carbon dynamics in semi-arid environments.     

Soil organic carbon distribution in relation to land use and its storage in a small watershed of the Loess Plateau, China

Soil organic carbon (SOC) is an important component in agricultural soil, and its stock is a major part of global carbon stocks. Estimating the SOC distribution and storage is important for improving soil quality and SOC sequestration. This study evaluated the SOC distribution different land uses and estimated the SOC storage by classifying the study area by land use in a small watershed on the Loess Plateau. The results showed that the SOC content and density were affected by land use. The SOC content for shrubland and natural grassland was significantly higher than for other land uses, and cropland had the lowest SOC content. The effect of land use on the SOC content was more significant in the 0-10 cm soil layer than in other soil layers. For every type of land use, the SOC content decreased with soil depth. The highest SOC density (0-60 cm) in the study area was found in shrublandII (Hippophae rhamnoides), and the other land uses decreased in the SOC density as follows: natural grassland > shrublandI (Caragana korshinskii) > abandoned cropland > orchard > level ground cropland > terrace cropland > artificial grassland. Shrubland and natural grassland were the most efficient types for SOC sequestration, followed by abandoned cropland. The SOC stock (0-60 cm) in this study was 23,584.77 t with a mean SOC density of 4.64 (0-60 cm).     

Soil degradation by land use change in an agropastoral area in Sardinia (Italy)

In recent decades the clearing of Mediterranean maquis along with the creation of new pastures has been a major factor of land degradation in Sardinia (Italy). This was due to an inadequate implementation of agricultural policies. Consequently, tillage and water erosion intensified over a wide area. The present work assesses the impacts of land use change on soil properties in a representative area of central-eastern Sardinia. Paired forest and pasture sampling sites were selected in relation to present land use, land suitability, and land use history. Different soil properties were considered: physical (sand, silt, clay, soil thickness, bulk density, and penetration resistance), chemical (pH, OC, N, C/N, Ca, Mg, Na, K, CEC, and BS), biological (BQI), and micromorphological (microporosity and microstructure). The comparison of forest and pasture soils showed a significant soil loss (in terms of soil thickness, −22%), and a clear decrease in organic carbon storage (−64% on average). An increase in bulk density (+ 44%) and a change in microporosity and its vertical distribution were also observed, respectively by field measurements and micromorphological quantification on digital images.     

Land use history and historical soil erosion at Albersdorf (northern Germany) — Ceased agricultural land use after the pre-historical period

The Holocene landscape history and historical soil erosion were reconstructed at Albersdorf (Schleswig-Holstein, Germany) from soils and colluvial layers. In contrast to many landscapes in central Europe, agricultural land use and soil erosion were more frequent during pre-historical times, whereas it has almost ceased after the advent of history. Pre-historical soil erosion rates from about 0.1 to 6.9 t ha^− 1 a^− 1 were reconstructed with no significant differences between the prehistoric cultural phases. The study of buried soils within the soil/soil-sediment-sequences provided evidence for an acceleration of soil formation processes probably as a consequence of excessive prehistoric woodland pasture on poor sandy soils.     

Reliability of an expert-based runoff and erosion model: Application of STREAM to different environments

During the last decades, the European loess belt has been confronted with a significant increase in environmental problems due to erosion on agricultural land. Spatially distributed runoff and erosion models operating at the catchment scale are therefore needed to evaluate the impact of potential mitigation measures. Expert-based models offer an alternative solution to process-based and empirical models, but their decision rules are only valid for the local conditions for which they have been derived. The STREAM model, which was developed in Normandy (France), has been applied in two Belgian catchments having a similar soil texture, as well as in a catchment of southern France differing by soil, land use and climate characteristics. The performance of hydrological models can be assessed for instance by calculating the Nash–Sutcliffe efficiency criterion (E_NS). When applied to Belgium, the model results are satisfactory to good after an adaptation of the decision rules (0.90 < E_NS < 0.93 for runoff predictions and 0.85 < E_NS < 0.89 for erosion predictions). Given the important environmental differences between Normandy and southern France, the model rules were also adapted for application in the latter environment. Unfortunately, the quality of runoff predictions was insufficient to simulate erosion in southern France. In conclusion, STREAM is a reliable model providing satisfactory runoff and erosion predictions in the regions where hortonian overland flow dominates. Nevertheless, an adaptation of decision rules based on local multi-scale (plot, field, catchment) data is needed, before running the model. STREAM can then serve as a decision support tool to design for instance flood control measures.     

Variation of soil respiration at three spatial scales: Components within measurements, intra-site variation and patterns on the landscape

Soil respiration is an important component of terrestrial carbon cycling and can be influenced by many factors that vary spatially. This research aims to determine the extent and causes of spatial variation of soil respiration, and to quantify the importance of scale on measuring and modeling soil respiration within and among common forests of Northern Wisconsin. The potential sources of variation were examined at three scales: [1] variation among the litter, root, and bulk soil respiration components within individual 0.1 m measurement collars, [2] variation between individual soil respiration measurements within a site (<1 m to 10 m), and [3] variation on the landscape caused by topographic influence (100 m to 1000 m). Soil respiration was measured over a two-year period at 12 plots that included four forest types. Root exclusion collars were installed at a subset of the sites, and periodic removal of the litter layer allowed litter and bulk soil contributions to be estimated by subtraction. Soil respiration was also measured at fixed locations in six northern hardwood sites and two aspen sites to examine the stability of variation between individual measurements. These study sites were added to an existing data set where soil respiration was measured in a random, rotating, systematic clustering which allowed the examination of spatial variability from scales of <1 m to 100+ m. The combined data set for this area was also used to examine the influence of topography on soil respiration at scales of over 1000 m by using a temperature and moisture driven soil respiration model and a 4 km² digital elevation model (DEM) to model soil moisture. Results indicate that, although variation of soil respiration and soil moisture is greatest at scales of 100 m or more, variation from locations 1 m or less can be large (standard deviation during summer period of 1.58 and 1.28 μmol CO₂ m⁻² s⁻¹, respectively). At the smallest of scales, the individual contributions of the bulk soil, the roots, and the litter mat changed greatly throughout the season and between forest types, although the data were highly variable within any given site. For scales of 1-10 m, variation between individual measurements could be explained by positive relationships between forest floor mass, root mass, carbon and nitrogen pools, or root nitrogen concentration. Lastly, topography strongly influenced soil moisture and soil properties, and created spatial patterns of soil respiration which changed greatly during a drought event. Integrating soil fluxes over a 4 km² region using an elevation dependent soil respiration model resulted in a drought induced reduction of peak summer flux rates by 37.5%, versus a 31.3% when only plot level data was used. The trends at these important scales may help explain some inter-annual and spatial variability of the net ecosystem exchange of carbon.     

Analysis and modeling of soil conservation measures in the Three Gorges Reservoir Area in China

Experimental plots were constructed in the Zhangjiachong Watershed of the Three Gorges Reservoir Area to evaluate soil erosion of traditional slope land farming and effects of soil conservation measures. Surface runoff and sediment from the watershed and each plot were collected and measured during 2004–2007. Field investigations indicated that hedgerows were the best for soil erosion control, followed by stone dike terraces and soil dike terraces. The Water Erosion Prediction Project (WEPP) model was used to simulate erosion of annual and rainfall events both at the watershed and plot levels. The low deviation, high coefficient of determination and model efficiency values for the simulations indicated that the WEPP model was a suitable model. The soil erosion rate distribution was modeled to determine where serious erosion would occur during rainfall events in the Zhangjiachong Watershed and so control measures can be taken.     

Influence of landuse on soil erosion risk in the Cuyaguateje watershed (Cuba)

Landuse changes may dramatically enhance erosion risk. Besides deforestation, also arable landuse may have an important influence on soil loss. We investigated the erosion risk in a 151 km² subwatershed of the Cuyaguateje watershed (Cuba) using the RUSLE model. It was found that the valleys used for agriculture have the highest erosion risk, with actual erosion surpassing soil loss tolerance. Over the period 1985–2000, about 14 km² of forest has been converted into arable land. As a result, the area with a very high erosion risk increased with 12%. On arable land it was found that the crop management factor C of a “tobacco/maize” rotation was 0.478, compared to 0.245 for a rotation of various crops (sweet potato, beans, maize, cassava and fallow). When maize in the “tobacco/maize” rotation was intercropped with a leguminous crop (hyacinth bean) the C factor decreased to a value of 0.369. Also contouring may halve soil loss on moderate slopes (< 10%) when high ridges are applied, which is in Cuba generally the case for maize, cassava and sweet potato.     

Magnitude of soil erosion on the northern slope of the Uluguru Mountains,Tanzania: Interrill and rill erosion

The magnitude of interrill and rill erosion was determined on the northern slopes of the Uluguru Mountains, Tanzania which is representative for larger areas of East African Arch Mountains, where population pressure is high and land degradation is severe. The aim of the study was to develop a database to support soil conservation in the area. The study was done on two distinct geomorphic units with respect to altitude and hence rainfall distribution pattern: mountain ridges with an altitude ranging from 1000 to 1500 masl and mean annual rainfall of 2300 mm and mountain foothills whose altitude and mean annual rainfall are 550 to 900 masl and 900 mm, respectively. Total soil loss was measured on 36 individual bounded plots measuring 1.2 m × 20 m using Gerlarch troughs on each day with rain from July 2000 to June 2001. The plots were located on six different geopedologic units, nine on mountain ridges and the rest on the mountain foothills. The slope gradient on the terrain ranged from 30% to 70%. The plots were put under maize cultivation as the main crop. Soil loss through rill erosion was estimated by volumetric measurements of rills on each soil erosion plot. The soil loss due to interrill erosion was obtained by subtracting soil loss through rill erosion from the total soil loss measured in the Gerlarch troughs. The results indicate that soil loss due to both interrill and rill erosion was very high with mean soil loss of 69 and 163 t/ha/year, respectively. Rill erosion accounted for about 58% of the total soil loss while interrill erosion contributed to the remaining 42%. Both interrill and rill erosion were higher in the mountain ridges with mean soil loss of 88 t/ha/year and 210 t/ha/year compared to 49 and 116 t/ha/year in the mountain foothills, respectively. Rill erosion was significantly higher (P ≤ 0.001) in all geopedologic units with slope gradient above 40% (mean soil loss ranged between 91 and 258 t/ha/year) compared to interrill erosion with mean soil loss varying from 41 to 115 t/ha/year. In geopedologic units with slope gradient above 60% both interrill and rill erosion were highly active while in geopedologic units with slope gradient below 40% the two processes were less active. The results demonstrate that rill erosion is more important than interrill erosion in the study area particularly where the slope gradient exceeds 40%. The results further show that the major part of the studied area has moderate interrill erosion (10–50 t/ha/year) and severe to very severe (> 100 t/ha/year) rill erosion. This study clarifies the magnitude of interrill and rill erosion which is important for designing soil conservation on agricultural fields.     

Sediment source identification in a semiarid watershed at soil mapping unit scales

Selective erosion and transport of silt and clay particles from watershed soil surfaces leads to enrichment of suspended sediments by size fractions that are the most effective scavengers of chemical pollutants. Thus, preferential transport of highly reactive size fractions represents a major problem relative to sediment/chemical transport in watersheds, and offsite water quality. The objective of this research was to develop an approach to identify sediment sources at a soil mapping unit scale for the purpose of designing site specific best management practices which affect greater reductions in runoff and erosion losses. Surface soil samples were collected along transects from each of the major 25 mapping units in six subwatersheds of the Walnut Gulch Experimental Watershed. Suspended sediments were collected from supercritical flumes at the mouth of each subwatershed. Laboratory analyses included basic soil/sediment physical and chemical properties, radioisotopes, and stable carbon isotopes, all by standard methods. Aggregation index (AI) values [100 · (1 − water dispersible clay / total clay)] were taken as an indicator of relative soil erodibility. Potential sediment yield index (PSYI) values were calculated by multiplying percent relative area for individual soil mapping units times (100 − AI). Particle size results indicated that suspended sediments were enriched in clay, relative to the watershed soils, by an average of 1.28. Clay enrichment ratios (ER) were significantly (P ≤ 0.01) and positively correlated with AI, an indication that these two parameters can be equated with erodibility and sediment yield. The PSYI values for the six subwatersheds ranged from 68.0 to 81.7. The stable carbon isotope data for the suspended sediments gave a C3 (shrubs) to C4 plant (grasses) ratio that ranged from 1.06 to 2.25, indicating greater erosion from the more highly erodible, shrub-dominated subwatersheds which also coincided with the highest PSYI values. Correlation coefficients determined individually for PSYI versus clay ER, C3/C4 plant ratios, and multivariate mixing model results were: 0.962 (P ≤ 0.01), 0.905 (P ≤ 0.01), and 0.816 (P ≤ 0.05), respectively. These statistically significant relationships support the accuracy of a potential sediment yield index approach for identifying suspended sediment sources at soil mapping unit scales.     

Effect of snow amount on runoff,soil loss and suspended sediment during periods of snowmelt in southern West Siberia

Surface runoff, soil loss, suspended sediment concentration (SSC), texture of eroded soils and suspended sediment were determined on slightly eroded chernozems (mouldboard fall-ploughed) during years with different amounts of snow in three areas of southern West Siberia (Predsalairye, Priobye and Kuznetsk hollow). These areas have different geomorphological and climatic characteristics and soils. Observations were made from 1969 to 2007. The soil loss during very low-snow and low-snow years did not exceed 2 t ha^− 1. After winters with normal amounts of snow, the runoff led to slight soil loss (2–5 t ha^− 1). Soil losses in high-snow and very high-snow years varied from slight to severe (4.8–15.8 t ha^− 1) depending on studied area. The main sediment exported during intensive snowmelt and the 1 mm of runoff transported from 35 to 150 kg ha^− 1 of soil material. The removal of soil particles < 0.01 mm (especially clay) prevailed during the initial and final stages of snowmelt. Clay removal by meltwater from the ploughed layer in high-snow and very high-snow years varied from 3300 to 4200 kg ha^− 1 and, in the initial and final stages of snowmelt clay removal, accounted for 1260–1,500 kg ha^− 1. Among the three studied regions, Predsalairye had decreased soil erosion resistance and was the area with the greatest danger of erosion.     

Responses of soil organic matter and greenhouse gas fluxes to soil management and land use changes in a humid temperate region of southern Europe

We studied the effects of soil management and changes of land use on soils of three adjacent plots of cropland, pasture and oak (Quercus robur) forest. The pasture and the forest were established in part of the cropland, respectively, 20 and 40 yr before the study began. Soil organic matter (SOM) dynamics, water-filled pore space (WFPS), soil temperature, inorganic N and microbial C, as well as fluxes of CO₂, CH₄ and N₂O were measured in the plots over 25 months. The transformation of the cropland to mowed pasture slightly increased the soil organic and microbial C contents, whereas afforestation significantly increased these variables. The cropland and pasture soils showed low CH₄ uptake rates (<1 kg C ha⁻¹ yr⁻¹) and, coinciding with WFPS values >70%, episodes of CH₄ emission, which could be favoured by soil compaction. In the forest site, possibly because of the changes in soil structure and microbial activity, the soil always acted as a sink for CH₄ (4.7 kg C ha⁻¹ yr⁻¹). The N₂O releases at the cropland and pasture sites (2.7 and 4.8 kg N₂O-N ha⁻¹ yr⁻¹) were, respectively, 3 and 6 times higher than at the forest site (0.8 kg N₂O-N ha⁻¹ yr⁻¹). The highest N₂O emissions in the cultivated soils were related to fertilisation and slurry application, and always occurred when the WFPS >60%. These results show that the changes in soil properties as a consequence of the transformation of cropfield to intensive grassland do not imply substantial changes in SOM or in the dynamics of CH₄ and N₂O. On the contrary, afforestation resulted in increases in SOM content and CH₄ uptake, as well as decreases in N₂O emissions.     

A simplified approach for estimating soil carbon and nitrogen stocks in semi-arid complex terrain

We investigated soil carbon (C) and nitrogen (N) distribution and developed a model, using readily available geospatial data, to predict that distribution across a mountainous, semi-arid, watershed in southwestern Idaho (USA). Soil core samples were collected and analyzed from 133 locations at 6 depths (n = 798), revealing that aspect dramatically influences the distribution of C and N, with north-facing slopes exhibiting up to 5 times more C and N than adjacent south-facing aspects. These differences are superimposed upon an elevation (precipitation) gradient, with soil C and N contents increasing by nearly a factor of 10 from the bottom (1100 m elevation) to the top (1900 m elevation) of the watershed. Among the variables evaluated, vegetation cover, as represented by a Normalized Difference Vegetation Index (NDVI), is the strongest, positively correlated, predictor of C; potential insolation (incoming solar radiation) is a strong, negatively correlated, secondary predictor. Approximately 62% (as R²) of the variance in the C data is explained using NDVI and potential insolation, compared with an R² of 0.54 for a model using NDVI alone. Soil N is similarly correlated to NDVI and insolation. We hypothesize that the correlations between soil C and N and slope, aspect and elevation reflect, in part, the inhibiting influence of insolation on semi-arid ecosystem productivity via water limitation. Based on these identified relationships, two modeling techniques (multiple linear regression and cokriging) were applied to predict the spatial distribution of soil C and N across the watershed. Both methods produce similar distributions, successfully capturing observed trends with aspect and elevation. This easily applied approach may be applicable to other semi-arid systems at larger scales.     

Modeling long-term soil carbon dynamics and sequestration potential in semi-arid agro-ecosystems

Long-term soil carbon (C) dynamics in agro-ecosystems is controlled by interactions of climate, soil and agronomic management. A modeling approach is a useful tool to understand the interactions, especially over long climatic sequences. In this paper, we examine the performance of the Agricultural Production Systems sIMulator (APSIM) to predict the long-term soil C dynamics under various agricultural practices at four semi-arid sites across the wheat-belt of eastern Australia. We further assessed the underlying factors that regulate soil C dynamics in the top 30 cm of soil through scenario analysis using the validated model. The results show that APSIM is able to predict aboveground biomass production and soil C dynamics at the study sites. Scenario analyses indicate that nitrogen (N) fertilization combined with residue retention (SR) has the potential to significantly slow or reverse the loss of C from agricultural soils. Optimal N fertilization (N_opt) and 100% SR, increased soil C by 13%, 46% and 45% at Warra, Wagga Wagga and Tarelee, respectively. Continuous lucerne pasture was the most efficient strategy to accumulate soil C, resulting in increases of 49%, 57% and 50% at Warra, Wagga Wagga and Tarlee, respectively. In contrast, soil C decreases regardless of agricultural practices as a result of cultivation of natural soils at the Brigalow site. Soil C input, proportional to the amount of retained residue, is a significant predictor of soil C change. At each site, water and nitrogen availability and their interaction, explain more than 59% of the variation in soil C. Across the four sites, mean air temperature has significant (P < 0.05) effects on soil C change. There was greater soil C loss at sites with higher temperature. Our simulations suggest that detailed information on agricultural practices, land use history and local environmental conditions must be explicitly specified to be able to make plausible predictions of the soil C balance in agro-ecosystems at different agro-ecological scales.     

Surface soil hydraulic properties in four soil series under different land uses and their temporal changes

The concepts of “genoform” and “phenoform” distinguish the genetically-defined soil series and the variation of soil properties resulted from different land uses and management practices. With the repeated field measurements over time, we attempted to understand the difference of soil hydraulic properties among different land uses for a given soil series, and their temporal dynamics. Four soil series (Glenelg, Hagerstown, Joanna, and Morrison) in Pennsylvania with contrasting textures, structures, and parent materials were investigated. Within each soil series, four common land uses (woodland, cropland, pasture, and urban) were examined. At each site of soil series–land use combination, field-saturated and near-saturated hydraulic conductivities, K(ψ), were measured at the soil surface using standard tension infiltrometers at water supply potentials (ψ) of − 0.12, − .06, − 0.03, − 0.02, − 0.01, and 0 m. Surface infiltration measurements were repeated at each site in May and October from 2004 to 2006. The analysis of variance indicated that the measurement time (May or October) had the greatest impact on all measured hydraulic conductivities (p < 0.001), followed by the land use (p < 0.05 for K_ψ = 0 and K_{ψ = − 0.06}) and soil series (p < 0.06 for K_{ψ = − 0.01} to K_{ψ = − 0.03}). The interactions between the time and land use and between the soil series and land use were statistically significant for K_ψ = 0 and K_{ψ = − 0.01.} When separated by the measurement time, land use showed greater impacts in October than in May, while soil series had greater impacts in May than in October. Among the four land uses, woodland showed less obvious temporal change compared to the other three land uses because of less human-induced impacts and more consistent ground cover. Other three land uses generally showed a higher hydraulic conductivity in May than in October due to the drier initial soil moisture condition and related management practices in the spring that gave rise to more significant macropore flow. The results suggested that the initial soil moisture is an important variable that drives the temporal variation of the surface soil hydraulic properties.     

Soil carbon turnover and sequestration in native subtropical tree plantations

Approximately 30% of global soil organic carbon (SOC) is stored in subtropical and tropical ecosystems but it is being rapidly lost due to continuous deforestation. Tree plantations are advocated as a C sink, however, little is known about rates of C turnover and sequestration into soil organic matter under subtropical and tropical tree plantations. We studied changes in SOC in a chronosequence of hoop pine (Araucaria cunninghamii) plantations established on former rainforest sites in seasonally dry subtropical Australia. SOC, δ¹³C, and light fraction organic C (LF C<1.6 g cm⁻³) were determined in plantations, secondary rainforest and pasture. We calculated loss of rainforest SOC after clearing for pasture using an isotope mixing model, and used the decay rate of rainforest-derived C to predict input of hoop pine-derived C into the soil. Total SOC stocks to 100 cm depth were significantly (P<0.01) higher under rainforest (241 t ha⁻¹) and pasture (254 t ha⁻¹) compared to hoop pine (176-211 t ha⁻¹). We calculated that SOC derived from hoop pine inputs ranged from 32% (25 year plantation) to 61% (63 year plantation) of total SOC in the 0-30 cm soil layer, but below 30 cm all C originated from rainforest. These results were compared to simulations made by the Century soil organic matter model. The Century model simulations showed that lower C stocks under hoop pine plantations were due to reduced C inputs to the slow turnover C pool, such that this pool only recovers to within 45% of the original rainforest C pool after 63 years. This may indicate differences in soil C stabilization mechanisms under hoop pine plantations compared with rainforest and pasture. These results demonstrate that subtropical hoop pine plantations do not rapidly sequester SOC into long-term storage pools, and that alternative plantation systems may need to be investigated to achieve greater soil C sequestration.     

Effectiveness of geotextiles in reducing runoff and soil loss: A synthesis

Despite geotextiles having potential for soil conservation, limited scientific data are available to assess the effects of geotextiles in reducing runoff and water erosion. Hence, the objective of this review is to analyse the effects of plot length (L) and other possible affecting factors [cover percentage (C, %), slope gradient (S), rainfall duration (D), rainfall intensity (I), sand, silt and clay contents, soil organic matter (SOM) content and geotextile type (natural or synthetic)] on the effectiveness of geotextiles in reducing soil and water loss, based on reported experimental data. From linear regressions, C (%) and soil sand, silt and clay contents are found to be the most important variables in reducing SLR (ratio of soil loss in bare plots to that in geotextile treated plots) for splash, C (%) for interrill and D (min) for rill and interrill erosion processes, respectively. Soil clay and silt contents and D are key variables in decreasing RR (ratio of runoff from bare plots to that from geotextile treated plots) for interrill, and clay content for rill and interrill erosion processes, respectively. The linear relationship between mean b-value (geotextile effectiveness factor in reducing soil loss) and L of all studies was not significant (P > 0.05). The same is true for the relationship between L and SLR, and L and RR. However, when L is added to an equation as an interaction term with C (%), geotextile cover is significantly (P < 0.05) more effective in reducing SLR on shorter plots than longer ones for both interrill and rill and interrill erosion processes. Buffer strip plots (area coverage ∼ 10%) with Borassus and Buriti mats have the highest b-values.     

Surface runoff and soil erosion in a natural regeneration area of the Brazilian Cerrado

The Brazilian Cerrado has been converted to farmland, and there is little evidence that this expansion will decrease, mainly because agriculture is the country’s main economic sector. However, the impacts of intense modification of land use and land cover on surface runoff and soil erosion are still poorly understood in this region. Here, we assessed surface runoff and soil loss in a woodland Cerrado area under a former pasture area, which was abandoned and has undergone a natural regeneration process for 7 years (RC). Its results were compared with that found in an undisturbed area of woodland Cerrado (CE), 40-month-old eucalyptus (3.0 × 1.8 m) (EU), and pasture under rotational grazing (PA). The study was conducted on Red Acrisol located in the Brazilian Cerrado. We performed rainfall simulations on a plot of 0.7 m² and using three constant rainfall intensities of 60, 90, and 120 mm h⁻¹ for 1 h. For each rainfall intensity, we carried out four repetitions using different plots in each treatment, i.e. 12 plots per treatment studied and 48 plots in total. We noted that the soil physical properties were improved in RC and, consequently, water infiltration and soil erosion control; RC presented surface runoff and soil loss different from EU and PA (α = 0.05). The macroporosity and soil bulk density affected surface runoff in RC and PA because the RC was used as pasture and is currently regenerating back to the cerrado vegetation. As the rainfall intensity increased, EU became more similar to PA, which showed the highest surface runoff and soil loss. Our findings indicate that natural regeneration processes (pasture to the cerrado vegetation) tend to improve the soil ecosystem services, improving infiltration and reducing surface runoff and soil erosion.     

基于CSLE模型的天山北坡西白杨沟流域土壤侵蚀定量评价

[目的]定量评价天山北坡西白杨沟流域水土流失土壤侵蚀状况,分析其分布特征,为区域水土保持以及生态环境建设提供科学依据。[方法]以新疆维吾尔自治区乌鲁木齐县西白杨沟流域为研究区,采用样地调查与地理信息系统(GIS)、遥感(RS)技术相结合方法和CSLE模型,对西白杨沟流域进行土壤水力侵蚀评价及侵蚀强度空间分布分析。[结果]天山北坡西白杨沟流域平均土壤侵蚀模数748.91 t/(km~2·a)。地形对土壤侵蚀强度影响明显,在坡度20°～40°区域,土壤侵蚀模数最高,为1 127.22～1 229.62 t/(km~2·a)。缓坡(20°)区域,坡度对土壤侵蚀模数呈正效应,而在陡坡(40°～70°)区域,坡度对土壤侵蚀模数呈负效应。土壤侵蚀主要发生在南坡、东南坡和东坡;不同土地利用方式对土壤水力侵蚀程度影响不同,表现为:呈灌木林地[1 709.80 t/(km~2·a)]有林地[1 389.40 t/(km~2·a)]天然牧草地[605.20 t/(km~2·a)]人工牧草地[334.71 t/(km~2·a)]水浇地[113.69 t/(km~2·a)]的趋势。[结论]土壤侵蚀强度总体以微度和轻度为主,强烈侵蚀、极强烈侵蚀、剧烈侵蚀主要分布在流域的中下游和下游;天山北坡西白杨沟流域侵蚀强度的空间分布与地形、土地利用、土壤性质联系紧密。     

Soil conservation planning at the small watershed level using RUSLE with GIS: a case study in the Three Gorge Area of China

The Three Gorge Project (TGP) of China necessitates the resettlement of over 1 million population (mostly farmers) to more rugged and isolated areas than their original settlements. Soil erosion is a serious environmental and production problem in this area. To decrease the risk on environmental impacts, there is an increasing demand for sound, and readily applicable techniques for soil conservation planning in the Three Gorge Areas (TGA). The objectives of the study were to develop and validate a soil erosion-predicting model based on the revised Universal Soil Loss Equation (RUSLE) in a geographic information systems (GIS) environment. The use of GIS to develop conservation-oriented watershed management strategies in the Wangjiaqiao watershed is presented. Data used for the RUSLE were either determined or taken from published literature pertaining to the Wangjiaqiao watershed. In combination with IDRISI, GIS software (Eastman, R.J., 1997. IDRISI for Windows: User's guide (Version 2.0). Clark University, Graduate School of Geography, Worcester, MA, Chapters 4–17) was used to evaluate different agricultural management strategies in terms of predicted soil loss in the watershed. This model allowed for easy assessment of soil erosion hazards under different crop and land management options over the entire watershed. The study revealed that the annual average soil loss rate from relatively flat agricultural land was approximately 26 t/ha, whereas 52 t/ha was found on the cultivated sloping lands, which constitutes a large proportion of soil loss in the watershed. In the watershed, approximately 38 ha of agricultural land had slopes >47% (25°) and should be reforested or returned to pasture. Contour tillage (CT) and contour farming with a seasonal no-till ridge (CTN) were most effective in reducing soil loss rates. If CT and CTN were implemented, approximately 31% and 70%, respectively, of the areas with soil loss >T_EP would be reduced to <T_EP. T_EP is soil loss tolerance for economic planning and was set at ≤10 t/ha year. In addition to soil loss reduction, the CTN has the potential to increase crop yield. Soil erosion hazards may be alleviated in over 91% of the agricultural lands if combined conservation measures including terraces, CTN, CT, and crop rotations were implemented in the watershed. The results of the study indicate that the RUSLE-GIS model is a useful tool for resource management and soil conservation planning. This technology is readily transferable and accessible to other land managers and agronomists in the TGA.