Assessment of soil erosion hazard in Kilie catchment,East Shoa,Ethiopia

This paper reports on a field study conducted in Kilie catchment, East Shoa Zone, Ethiopia to assess the rate of soil erosion by employing a soil loss prediction model (Universal Soil Loss Equation) integrated with in remote sensing and geographical information systems (RS/GIS), environment and gully measurement techniques. The final soil erosion risk map was produced after multiplication of the six factors involved in the USLE and RS/GIS. Gully measurement showed that the erosion rate is higher for the upland areas than the lowlands due to inappropriate soil and water conservation measures, free grazing by animals and conversion of hillside areas into farmlands. About 97·04 per cent of the study catchment falls within a range of 0–10 t ha⁻¹ yr⁻¹ sheet/rill erosion rate. We found that 2·17 per cent of the study area in the uplands has a soil erosion rate falling between 10 and 20 t ha⁻¹ yr⁻¹. About 0·8 per cent of the study area in the uplands is hit by severe sheet/rill erosion rate within the range of 20–60 t ha⁻¹ yr⁻¹. Gully erosion extent in the study area was evaluated through gully measurement and quantification methods. Gully density of 67 m ha⁻¹ was recorded in the catchment. The gully to plot area ratio was found to be 0·14 on average. Hence, in the upland areas, sustainable land management practices are required in order to reduce the rate of soil erosion. Copyright © 2011 John Wiley & Sons, Ltd.     

Impacts of longterm conservation measures on ecosystem services in Northwest Ethiopia

A Soil Conservation Research Program (SCRP) has been on-going in Anjeni Watershed, Amhara Region, Ethiopia since the 1980s, focussing particularly on soil-based, graded fanya juu terraces. This study was carried out to examine the long-term impacts of these soil and water conservation measures in improving ecosystem services. A comparative analysis was made with a non-treated 100 ha adjacent watershed (Zikrie). The Revised Universal Soil Loss Equation (RUSLE) was used in a geographic information system (GIS) to quantify soil loss. Representative soil samples were taken 30 cm deep soil pits in the loss and deposition zones in the terraced Anjeni and topo-sequential soil samples on both watersheds. Laboratory analysis was carried out at the National Soil Testing Laboratory (NSTL) of Ethiopia. Soil texture, pH and OC were analyzed for the 91 soil samples. A GIS analysis of the RUSLE factors was made on a 5 m grid cell basis. The mean annual soil loss rate in Anjeni was estimated to be 37 t ha^-1 yr^-1, while that of the adjacent non-conserved Zikrie was 45 t ha^-1 yr^-1. The total estimated soil loss in Anjeni watershed was 4214 t yr^-1. River valleys in the Anjeni watershed had the maximum mean annual estimated soil loss hazard (86 t ha^-1 yr^-1). Cultivated land had medium mean annual estimated soil loss (44 t ha^-1 yr^-1) due to the soil conservation works. Supporting the soil-based graded fanya juu terraces with biological soil conservation measures is important for the stability of the ecosystem.     

Comparison of two methods to assess the carbon budget of forest biomes in the Former Soviet Union

The sink of CO₂ and the C budget of forest biomes of the Former Soviet Union (FSU) were assessed with two distinct methods: (1) ecosystem/ecoregional, and (2) forest statistical data. The ecosystem/ecoregional method was based on the integration of ecoregions (defined with a GIS analysis of several maps) with soil/vegetation C data bases. The forest statistical approach was based on data on growing stock, annual increment of timber, and FSU yield tables. Applying the ecosystem/ecoregional method, the area of forest biomes in the FSU was estimated at 1426.1 Mha (10⁶ ha); forest ecosystems comprised 799.9 Mha, non-forest ecosystems and arable land comprised 506.1 and 119.9 Mha, respectively. The FSU forested area was 28% of the global area of closed forests. Forest phytomass (i.e., live plant mass), mortmass (i.e., coarse woody debris), total forest plant mass, and net increment in vegetation (NIV) were estimated at 57.9 t C ha^?1, 15.5 t C ha^?1, 73.4 t C ha^?1, and 1.0 t C ha^?1 yr^?1, respectively. The 799.9 Mha area of forest ecosystems calculated in the ecosystem/ecoregional method was close to the 814.2 Mha reported in the FSU forest statistical data. Based on forest statistical data forest phytomass was estimated at 62.7 t C ha^?1, mortmass at 37.6 t C ha^?1; thus the total forest plant mass C pool was 100.3 t C ha^?1. The NIV was estimated at 1.1 t C ha^?1 yr^?1. These estimates compared well with the estimates for phytomass, total forest plant mass, and NIV obtained from the ecosystem/ecoregional method. Mortmass estimated from the forest statistical data method exceeded the estimate based on the ecosystem/ecoregional method by a factor of 2.4. The ecosystem/ecoregional method allowed the estimation of litter, soil organic matter, NPP (net primary productivity), foliage formation, total and stable soil organic matter accumulation, and peat accumulation (13.9 t C ha^?1, 125.0 t C ha^?1, 3.1 t C ha^?1 yr^?1, 1.4 t C ha^?1 yr^?1, 0.11, and 0.056 t C ha^?1 yr^?1, respectively). Based on an average value of NEP (net ecosystem productivity) from the two methods, and following a consideration of anthropogenic influences, FSU forests were estimated to be a net sink of approximately 0.5 Gt C yr^?1 of atmospheric C.     

Soil Erosion in Steep Road Cut Slopes in Palencia (Spain)

Construction associated to land development, such as roads and railroads, promote severe land degradation. Cutslope sediment yield is one of the major pollutants on waters close to the road and railroad network. To estimate road impact, soil erosion (E), sediment yield (SY) and morphological evolution of a railroad cut in Palencia (Spain), were studied using erosion nails, during the periods 1998–1999, 1999–2000 and 2000–2010. Data from two sample plots were analyzed by an ANOVA for repeated measures. Slope morphological evolution was estimated using a cubic polynomial regression, while E and SY were calculated by integration. The top and the toe of the slope eroded and accumulated 0·5 m respectively, evolving into a concave/convex slope profile. The mean measured E was 220 Mg ha⁻¹ y⁻¹. SY was 31 Mg ha⁻¹ y⁻¹, ranging from 109 Mg ha⁻¹ y⁻¹ to 24 Mg ha⁻¹ y⁻¹. Sediment yield was 4·5 times higher during the first year, than in all subsequent years. Results showed a decreasing trend and a stabilization in E and SY rates. However, both rates remain high and critical over the analyzed time, with regards to soil formation, water protection, land degradation and infrastructure maintenance. Copyright © 2015 John Wiley & Sons, Ltd.     

Soil loss estimation using rusle model to prioritize erosion control in KELANI river basin in Sri Lanka

Soil erosion contributes negatively to agricultural production, quality of source water for drinking, ecosystem health in land and aquatic environments, and aesthetic value of landscapes. Approaches to understand the spatial variability of erosion severity are important for improving landuse management. This study uses the Kelani river basin in Sri Lanka as the study area to assess erosion severity using the Revised Universal Soil Loss Equation (RUSLE) model supported by a GIS system. Erosion severity across the river basin was estimated using RUSLE, a Digital Elevation Model (15 × 15 m), twenty years rainfall data at 14 rain gauge stations across the basin, landuse and land cover, and soil maps and cropping factors. The estimated average annual soil loss in Kelani river basin varied from zero to 103.7 t ha-1 yr⁻¹, with a mean annual soil loss estimated at 10.9 t ha⁻¹ yr⁻¹. About 70% of the river basin area was identified with low to moderate erosion severity (<12 t ha−1 yr⁻¹) indicating that erosion control measures are urgently needed to ensure a sustainable ecosystem in the Kelani river basin, which in turn, is connected with the quality of life of over 5 million people. Use of this severity information developed with RUSLE along with its individual parameters can help to design landuse management practices. This effort can be further refined by analyzing RUSLE results along with Kelani river sub-basins level real time erosion estimations as a monitoring measure for conservation practices.     

Soil carbon sequestration in sub‐Saharan Africa: a review

Restoration of degraded soils is a development strategy to reduce desertification, soil erosion and environmental degradation, and alleviate chronic food shortages with great potential in sub‐Saharan Africa (SSA). Further, it has the potential to provide terrestrial sinks of carbon (C) and reduce the rate of enrichment of atmospheric CO₂. Soil organic carbon (SOC) contents decrease by 0 to 63 per cent following deforestation. There exists a high potential for increasing SOC through establishment of natural or improved fallow systems (agroforestry) with attainable rates of C sequestration in the range of 0·1 to 5·3 Mg C ha⁻¹ yr⁻¹. Biomass burning significantly reduces SOC in the upper few centimeters of soil, but has little impact below 10 to 20 cm depth. The timing of burning is also important, and periods with large amounts of biomass available generally have the largest losses of SOC. In cultivated areas, the addition of manure in combination with crop residues and no‐till show similar rates of attainable C sequestration (0 to 0·36 Mg C ha⁻¹ yr⁻¹). Attainable rates of SOC sequestration on permanent cropland in SSA under improved cultivation systems (e.g. no‐till) range from 0·2 to 1·5 Tg C yr⁻¹, while attainable rates under fallow systems are 0·4 to 18·5 Tg C yr⁻¹. Fallow systems generally have the highest potential for SOC sequestration in SSA with rates up to 28·5 Tg C yr⁻¹. Copyright © 2005 John Wiley & Sons, Ltd.     

Long-term changes in organic matter of woodland soils cleared for arable cropping in Zimbabwe

Subsistence farmers in Africa depend largely on the soil organic matter to sustain crop productivity. Long-term changes in soil organic carbon and nitrogen were measured after woodland clearance for smallholder subsistence farming or for commercial farming. The contents of organic carbon and nitrogen in soil under reference woodlands were largest (53.3 t C ha⁻¹, 4.88 t N ha⁻¹) in a red clay soil (∼ 50% clay + silt), followed by a granitic sand (∼ 12% clay + silt; 22.8 t C ha⁻¹, 1.47 t N ha⁻¹) and least (19.5 t C ha⁻¹, 0.88 t N ha⁻¹) in a Kalahari sand (∼ 5% clay + silt). Organic carbon declined rapidly under cultivation to attain new equilibria within 10 years on all smallholdings. Greatest losses occurred in soils that initially contained most carbon and nitrogen in the order: red clay (22.4 t C ha⁻¹ and 1.0 t N ha⁻¹) > granitic sand (13.2 t C ha⁻¹ and 0.8 t N ha⁻¹) > Kalahari sand (10.6 t C ha⁻¹ and 0.5 t N ha⁻¹). On the clay soil, commercial farming with intensive use of mineral fertilizers and incorporation of maize stover led to more gradual decline: at equilibrium, contents of carbon and nitrogen were 15 t C ha⁻¹ and 1.7 t N ha⁻¹ greater than on smallholdings with similar soil and climate. In the Kalahari sand the δ¹³C of organic C remained constant after woodland clearance, and maize contributed less than 10% of the total C even after 55 years. The δ¹³C signature increased slightly with increasing duration of cultivation by smallholders in the granitic sands and red clay soil where maize contributed 29% and 35% of the C at equilibrium. Under more productive commercial farming, the carbon derived from maize accounted for 50% of the total after 10 years of cultivation and 67% at equilibrium. The persistence of woodland carbon in the sandy soil is attributed to chemical stabilization resulting from large concentrations of lignin and polyphenols in the tree litter, or as charcoal.     

Terrain attributes, landform segmentation, and soil redistribution

The ¹³⁷Cs technique has greatly expanded our knowledge of the topography–soil redistribution relationship. For the technique to be useful in upscaling of process models and regional-scale conservation planning, we must be able to show that a consistent relationship exists between ¹³⁷Cs-derived soil redistribution rates and terrain attributes in a given region. In this paper, the association between ¹³⁷Cs-derived soil redistribution rates and quantitatively defined landform elements was examined at nine hummocky terrain sites in southern Saskatchewan, Canada. Shoulder (SH) elements with convex plan curvatures had the highest mean soil loss rates of 33 t ha⁻¹ yr⁻¹, followed closely by other SH and backslope (BS) elements. The erosional behavior of level elements (i.e. those with gradients less than 3°) was highly dependent on the specific dispersal area (SDA) of the element—elements with high dispersal areas were dominantly erosional (mean soil loss of 14 t ha⁻¹ yr⁻¹), whereas level elements with low dispersal areas were depositional (mean soil gain of 15 t ha⁻¹ yr⁻¹). Doubly concave footslope (FS) elements had mean soil gain of 10 t ha⁻¹ yr⁻¹. The dispersion of values across the nine sites was much greater for the depositional units than the erosional units, indicating a complex relationship between deposition and terrain attributes in the depositional units. The results clearly indicate that regional-scale patterns of soil redistribution can be developed using the ¹³⁷Cs technique.     

Effect of land management on runoff and soil losses from two small watersheds in St Lucia

The influence of land use on runoff and soil loss was assessed on two small watersheds in the Eastern Caribbean island of St Lucia, under contrasting land management regimes. The data generated from these watersheds revealed that the soil losses from an intensively cultivated agricultural watershed were 20‐times higher in magnitude than that of a forested watershed both for peak rainfall event and for total duration of analysis. This was due to higher surface runoff rates and exposure of soil to direct raindrop impact within cultivated areas. Whereas the forest canopy cover in combination with higher infiltration capacities of the forested land reduced the erosive runoff from the forest watershed and thus the soil loss. Moreover, the energy intensities of large storms in excess of 40 mm were estimated and found to range between 400 MJ mm ha⁻¹ h⁻¹ and 1834 MJ mm ha⁻¹ h⁻¹. 1

1 Megajoules‐millimeters per hectare‐hour.

Soil loss from the agricultural watershed was strongly correlated (R² = 0·85) to storm energy‐intensity (EI₃₀). However, the correlation of soil loss with the EI₃₀ (R² = 0·71) was poor for the forest watershed due to the effect of canopy vegetation, which significantly reduced the energy of raindrop impact. Over the study period, cumulative soil losses were 10·0 t ha⁻¹ for the agricultural site and 0·5 t ha⁻¹ for the forest site. 2

2 Metric tons per hectare.

The largest storm observed during the study period resulted in erosion losses of 3·78 t ha⁻¹ and 0·2 t ha⁻¹ from the agricultural and forest sites respectively. The regression models were developed using the measured data for prediction of runoff and soil loss over the watersheds of St Lucia under similar conditions. This study contributed towards efficient watershed management planning and implementation of suitable water conservation measures in St Lucia. Copyright © 2005 John Wiley & Sons, Ltd.     

Soil microbiological and biochemical properties affected by plant growth and different long-term fertilisation

The purpose of this study was to measure the effects of plant growth on soil microbial biomass C (C_mic) and soil enzyme activities. In a pot experiment using spring barley and sugar beet, we investigated the response of C_mic, hot water extractable C and N fractions (C_hwe, N_hwe), and enzyme activities involved in C, N and P cycling in a loess-derived Chernozem from Bad Lauchstädt (Central Germany). The study site has been receiving the same fertilisation treatments for 100 years. The soil originated from plots fertilised with 15 t ha⁻¹ farmyard manure (FYM) year⁻¹ + mineral fertiliser (NPK), or 15 t ha⁻¹ FYM year⁻¹, or NPK or from an unfertilised control. Pots were sampled monthly, and alkaline phosphatase- (AP), β-glucosidase- and protease-activities were analysed. At the beginning and the end of study, levels of C_mic, C_hwe and N_hwe were also measured. All three enzyme activities and C_mic were significantly and positively correlated with C_org and C_hwe. Results suggest that the enzyme activities measured originated mostly from microorganisms and that C_hwe is an important C source for soil microorganisms. β-Glucosidase and AP activities were higher in summer months than at other times. In contrast, protease activity changed only slightly during the growing period.     

Annual emissions of nitrous oxide and nitric oxide from a wheat–maize cropping system on a silt loam calcareous soil in the North China Plain

Nitrogen amendment followed by flooding irrigation is a general management practice for a wheat–maize rotation in the North China Plain, which may favor nitrification and denitrification. Consequently, high emissions of nitrous oxide (N₂O) and nitric oxide (NO) are hypothesized to occur. To test this hypothesis, we performed year-round field measurements of N₂O and NO fluxes from irrigated wheat–maize fields on a calcareous soil applied with all crop residues using a static, opaque chamber measuring system. To interpret the field data, laboratory experiments using intact soil cores with added carbon (glucose) and nitrogen (nitrate, ammonium) substrates were performed. Our field measurements showed that pulse emissions after fertilization and irrigation/rainfall contributed to 73% and 88% of the annual N₂O and NO emissions, respectively. Soil moisture and mineral nitrogen contents significantly affected the emissions of both gases. Annual emissions from fields fertilized at the conventional rate (600 kg N ha⁻¹ yr⁻¹) totaled 4.0 ± 0.2 and 3.0 ± 0.2 kg N ha⁻¹ yr⁻¹ for N₂O and NO, respectively, while those from unfertilized fields were much lower (0.5 ± 0.02 kg N ha⁻¹ yr⁻¹ and 0.4 ± 0.05 kg N ha⁻¹ yr⁻¹, respectively). Direct emission factors (EF_ds) of N₂O and NO for the fertilizer nitrogen were estimated to be 0.59 ± 0.04% and 0.44 ± 0.04%, respectively. By summarizing the results of our study and others, we recommended specific EF_ds (N₂O: 0.54 ± 0.09%; NO: 0.45 ± 0.04%) for estimating emissions from irrigated croplands on calcareous soils with organic carbon ranging from 5 to 16 g kg⁻¹. Nitrification dominated the processes driving the emissions of both gases following fertilization. It was evident that insufficient available carbon limited microbial denitrification and thus N₂O emission. This implicates that efforts to enhance carbon sink in calcareous soils likely increase their N₂O emissions.     

Effect of surface-casting earthworms on the transport of phosphorus and nitrogen in surface runoff from pasture

Treatment of a soil under permanent pasture with carbaryl (a broad spectrum carbamate biocide) resulted in a 2-fold increase in the volume of surface runoff. This was attributed to a 3-fold reduction in infiltration rate as a result of litter accumulation at the soil surface in the absence of surface-casting earthworm activity. The amounts of dissolved inorganic P (DIP), NH⁺₄-N, and NO^?₃-N in surface runoff from pasture treated with carbaryl (1.18, 9.53 and 4.25 kg ha^?1 yr^?1, respectively) were appreciably greater than those from untreated pasture (0.31, 1.63 and 0.52 kg ha^?1 yr^?1). This was attributed to the large amounts of DIP, NH⁺₄-N, and NO^?1₃-N released from decomposing litter. Following incubation at 4°C for 18 days the release of DIP, NH⁺₄-N and NO^?₃-N from litter was 160, 1600 and 950 μg g^?1, respectively. Losses of particulate P and sediment in surface runoff were lower in the absence (0.31 and 290 kg ha^?1 yr^?1, respectively) than in the presence (0.56 and 1120 kg ha^? yr^?1) of surface casts, pointing to the importance of surface casts as a source of sediment. Surface casts accounted for 45 and 75%, respectively, of the annual loading of particulate P and sediment in surface runoff. Nevertheless, the total loss in surface runoff of P and N forms was increased substantially when the production of earthworm casts was eliminated     

Assessing soil erosion and control factors by the radiometric technique in the Boussouab catchment,Eastern Rif,Morocco

In the Eastern Rif of N Morocco, soil conservation is seriously threatened by water erosion. Large areas of soil have reached an irreversible state of degradation. In this study, the ¹³⁷Cs technique was used to quantify erosion rates and identify the main factors involved in the erosion process based on a representative catchment of the Eastern Rif. To estimate erosion rates in terms of the main factors affecting soil losses, samples were collected taking into account the lithology, slope and land use along six selected transects within the Boussouab catchment. The transects were representative of the main land uses and physiographic characteristics of that Rif sector. The reference inventory for the area was established at a stable, well preserved, matorral site (value of 4250 Bq m^− 2). All the sampling sites were eroded and ¹³⁷Cs inventories varied widely (between 245 and 3670 Bq m^− 2). The effective soil losses were also highly variable (between 5.1 and 48.8 t ha^− 1 yr^− 1). Soil losses varied with land use. The lowest average values were on matorral and fallow land (10.5 and 15.2 t ha^− 1 yr^− 1, respectively) but much higher with alfa vegetation or cereal crops (31.6 and 27.3, respectively). The highest erosion rate was on a badland transect at the more eroded part of the catchment, with rates exceeding 40 t ha^− 1 yr^− 1 and reaching a maximum of 48.8 t ha^− 1 yr^− 1.The average soil losses increased by more than 100% when the slope increased from 10° (17.7 t ha^− 1 yr^− 1) to 25° (40. 8 t ha^− 1 yr^− 1). Similar results were obtained when comparing erosion rates in soils that were covered by matorral with respect to those under cultivation. Lithology was also a key factor affecting soil loss. Soils on marls were more erodible and the average erosion rates reached 29.36 t ha^− 1 yr^− 1, which was twice as high as soils on the glacis and old fluvial terraces (average rates of 14.98 t ha^− 1 yr^− 1). The radiometric approach was very useful to quantify erosion rates and to examine the pattern of soil movement. The analysis of main erosion factors can help to promote rational soil use and establish conservation strategies in the study area.     

Proton Budget for a Japanese Cedar Forest Ecosystem

The proton budget for a Japanese cedar (Cryptomeria japonica) forest in Gunma Prefecture, Japan, was studied by estimating biogeochemical fluxes. The proton budgets were estimated for three individual compartments of the ecosystem: vegetation canopy, and the upper (O horizon + 0–10 cm) and lower (10–100 cm) soil layers. The dominant proton sources in the compartments were atmospheric deposition (1.2 kmol ha^?1 yr^?1), nitrification (5.1 kmol, ha^?1 yr^?1) and base-cation uptake by vegetation (8.0 kmol, ha^?1 yr^?1) respectively. These proton sources were neutralized almost completely within the individual compartments mainly by base-cation release from the canopy or the soil. The sum of internal proton sources was five times as large as that of external ones. Nitrogen input from the atmosphere was 2.2 kmol ha^?1 yr^?1, whereas its output from the lower soil layer was 3.9 kmol ha^?1 yr^?1, indicating that a net loss of nitrogen occurred in the ecosystem. However, this did not cause the acidification of soil leachates because of a sufficient release rate of base cations from the soil.     

Nutrient losses from rain‐fed bench terraced cultivation systems in high rainfall areas of the mid‐hills of Nepal

Between the elevations of 1000 and 2000 m in the mid‐hills of Nepal, over 12 million people subsist on land‐holdings of less than 0·5 ha. These farmers have limited access to commercial inputs such as fertilisers and are reliant on organic manures for soil fertility maintenance. Participatory research was conducted with farmers on bari land (upper slope rain‐fed crop terraces) in the hill community of Landruk (bench terraces 0–5° slope, 3000–3500 mm annual rainfall, which aimed to develop soil and water management interventions that controlled erosion without resulting in high leaching, and so were effective in minimising total nutrient losses. Interventions tested were the control of water movement through diversion of run‐on and planting fodder grasses on terrace risers on bench terraces. The interventions were effective in reducing soil loss from the bari land in comparison with existing farmer practices, but no effect was observed on nutrient losses in solution form through runoff and leaching. Losses of NO₃‐N in leachate ranged from 17·3 to 99·7 kg ha⁻¹ yr⁻¹, but only 0·7 to 5·6 kg ha⁻¹ yr⁻¹ in runoff. The overall nutrient balance suggests that the system is not sustainable. Fertility is heavily dependent on livestock inputs and if the current trends of declining livestock numbers due to labour constraints continue, further losses in productivity can be expected. However, farmers are interested in interventions that tie ecosystem services with productivity enhancement and farmers' priorities should be used as entry points for promoting interventions that are system compatible and harness niche opportunities. Copyright © 2007 John Wiley & Sons, Ltd.     

Effect of straw biochar application on soil carbon,greenhouse gas emissions and nitrogen leaching: A vegetable crop rotation field experiment

Intensive vegetable crop systems are rapidly developing, with consequences for greenhouse gas (GHGs) emissions, nitrogen leaching and soil carbon. We undertook a field trial to explore the effect of biochar application (0, 10, 20 and 40 t ha⁻¹) on these factors in lettuce, water spinach and ice plant rotation. Our results show that the 20 and 40 t ha⁻¹ soil treatments resulted in the SOC content being 26.3% and 29.8% higher than the control (0 t ha⁻¹), respectively, with significant differences among all treatments (p < .05). Biochar application caused N₂O emissions to decrease during the lettuce and water spinach seasons, by 1.5%–33.6% and 12.4%–40.5%, respectively, compared the control, with the 20 t ha⁻¹ application rate resulting in the lowest N₂O emissions. Biochar also decreased the dissolved nitrogen (DN) concentration in leachate by 9.8%–36.2%, following a 7.3%–19.9% reduction in dissolved nitrogen in the soil. Similarly, biochar decreased the nitrate (NO₃⁻) concentrations in leachate by 3.9%–30.2%, following a 3.8%–16.7% reduction in the soil nitrate level. Overall, straw biochar applied at rate of 20 t ha⁻¹ produced the lowest N₂O emissions and N leaching, while, increasing soil carbon.     

The assessment of soil loss by water erosion in China

Soil erosion is a major environmental problem in China. Planning for soil erosion control requires accurate soil erosion rate and spatial distribution information. The aim of this article is to present the methods and results of the national soil erosion survey of China completed in 2011. A multi-stage, unequal probability, systematic area sampling method was employed. A total of 32,948 sample units, which were either 0.2–3 km² small catchments or 1 km² grids, were investigated on site. Soil erosion rates were calculated with the Chinese Soil Loss Equation in 10 m by 10 m grids for each sample unit, along with the area of soil loss exceeding the soil loss tolerance and the proportion of area in excess of soil loss tolerance relative to the total land area of the sample units. Maps were created by using a spatial interpolation method at national, river basin, and provincial scales. Results showed that the calculated average soil erosion rate was 5 t ha⁻¹ yr⁻¹ in China, and was 18.2 t ha⁻¹ yr⁻¹ for sloped, cultivated cropland. Intensive soil erosion occurred on cropland, overgrazing grassland, and sparsely forested land. The proportions of soil loss tolerance exceedance areas of sample units were interpolated through the country in 250 m grids. The national average ratio was 13.5%, which represents the area of land in China that requires the implementation of soil conservation practices. These survey results and the maps provide the basic information for national conservation planning and policymaking.     

Calculating critical loads of acid deposition with PROFILE — A steady-state soil chemistry model

A steady state soil chemistry model was used to calculate the critical load of acidity for forest soils and surface waters at Lake GÄrdsjön in S.W. Sweden. The critical load of all acid precursors (potential acidity) for the forest soil is 1.64 kmol_c ha^?1 yr^?1, and 1.225 kmol_c ha^?1 yr^?1 for surface waters. For the most sensitive receptor, the critical load is exceeded by 1.0 kmol_c ha^?1 yr^?1, and a 80% reduction in S deposition is required, if N deposition remains unchanged. The critical load is largely affected by the present immobilization of N in the terrestrial ecosystem which is higher than the base cation uptake. The model, PROFILE, is based on mass balance calculations for the different soil layers. From measurable soil properties, PROFILE reproduces the present stream water composition as well as present soil solution chemistry. The model calculates the weathering rate from independent geophysical properties such as soil texture and mineral composition.     

CARBON BUDGET AND SEQUESTRATION POTENTIAL IN A SANDY SOIL TREATED WITH COMPOST

The effects of compost application on soil carbon sequestration potential and carbon budget of a tropical sandy soil was studied. Greenhouse gas emissions from soil surface and agricultural inputs (fertiliser and fossil fuel uses) were evaluated. The origin of soil organic carbon was identified by using stable carbon isotope. The CO₂, CH₄ and N₂O emissions from soil were estimated in hill evergreen forest (NF) plot as reference, and in the corn cultivation plots with compost application rate at 30 Mg ha⁻¹ y⁻¹ (LC), and at 50 Mg ha⁻¹ y⁻¹ (HC). The total C emissions from soil surface were 8·54, 10·14 and 9·86 Mg C ha⁻¹ y⁻¹ for NF, HC and LC soils, respectively. Total N₂O emissions from HC and LC plots (2·56 and 3·47 kg N₂O ha⁻¹ y⁻¹) were significantly higher than from the NF plot (1·47 kg N₂O ha⁻¹ y⁻¹). Total CO₂ emissions from fuel uses of fertiliser, irrigation and machinery were about 10 per cent of total CO₂ emissions. For soil carbon storage, since 1983, it has been increased significantly (12 Mg ha⁻¹) under the application of 50 Mg ha⁻¹ y⁻¹ of compost but not with 30 Mg ha⁻¹ y⁻¹. The net C budget when balancing out carbon inputs and outputs from soil for NF, HC and LC soils were +3·24, −2·50 and +2·07 Mg C ha⁻¹ y⁻¹, respectively. Stable isotope of carbon (δ¹³C value) indicates that most of the increased soil carbon is derived from the compost inputs and/or corn biomass. Copyright © 2011 John Wiley & Sons, Ltd.     

Trace element release from forest floor can be monitored by ion exchange resin tubes

Risk assessment of heavy metal input into forest ecosystems requires information about metal fluxes from the forest floor (organic layer) into the mineral soil. Common methods for the monitoring of element fluxes are generally time‐consuming and expensive. Additionally, the reliability of the results is in part contested especially for trace elements, showing very low concentrations which are sometimes even below analytical detection limit. We used ion exchange resin tubes installed below the forest floor to determine heavy metal and As fluxes at 25 forest monitoring sites in Germany. Chloride tracer experiments and the comparison of our data with throughfall and lysimeter data, determined within the Level II monitoring network, proved the accuracy of our method. Mean trace element fluxes based on the resin method were 50 g As ha^–1 yr^–1, 2 g Cd ha^–1 yr^–1, 168 g Cu ha^–1 yr^–1, 176 g Ni ha^–1 yr^–1, and 186 g Pb ha^–1 yr^–1.The results show that the organic layer may change into a source of heavy metals after emission has decreased.