Cultivated Sites Research Articles

Earthworm indicators as tools for soil monitoring, characterization and risk assessment. An example from the national Bioindicator programme (France)

Considering the limited number of bioindicators available to assess soil quality, a national research programme was set up in France to develop such indicators (2006-2012), the Bioindicator programme. This programme tested 47 biological parameters (i.e. microorganisms, fauna, flora) including earthworms, in several sites differing in terms of land use, contamination type - PAHs or metals - and pollution levels. The present study proposes some study objectives for bioindicator approaches, based on the earthworm results from the programme. Therefore, different earthworm descriptors were tested at the community level (e.g. abundance, biomass, species and functional structures, and ecological traits) as well as the organism level (i.e. measuring the metallothionein coding gene expression level in earthworms). The present results, obtained from the programme's spring 2009 sampling campaign, discriminated among the different descriptors and showed that earthworm and endogeic abundance as well as the individual weight of endogeics seem to be good indicators in non-contaminated (cultivated) sites, while the ecological structure, namely the proportion of anecic vs. endogeic species, and the proportion of non-vulnerable species should be used as indicators of contaminated soils. Furthermore, the first results obtained for Lumbricus terrestris and L. rubellus rubellus are encouraging as they show that metallothionein expression increases in metal-contaminated soils. The relevance of these descriptors, which have to be considered in study objectives, requires the analysis of 2010 results.

Impact of Land Use Change and Soil Erosion in Upper Mississippi River Valley on Soil Organic Carbon Retention and Greenhouse Gas Emissions

The dynamics of soil organic carbon (SOC) are affected by many factors including land use, management history, soil type, climate, and soil landscape processes. The primary objective of this research was to compare the storage of SOC on sloping woodland and cropland landscapes of northwestern Illinois. The cropland area was cultivated using a moldboard plow system for 125 years, and then the primary tillage was changed to chisel plow for the last 25 years. The woodland area was never cleared or cultivated. The SOC concentrations of various soil layers, to a depth of 0.5 m, were measured. The woodland landscape had significantly higher SOC in the surface layers on all landscape segments than at the cultivated site. For both land uses, the subsurface layers had similar SOC levels. Results suggested that the cropland land- scape retained 52% of the total SOC on a volumetric basis during the last 150 years of cultivation, soil erosion, and agricultural use. The other 48% of the SOC was either deposited in the water or released to the atmosphere. Results suggest that if mesic-frigid temperature line moved north because of climate change, then the current uncultivated forest soils would be used for cropland, and additional SOC will be released to either the stream or atmosphere and not maintained in soil even with a chisel plow system.

Plant species effects on soil carbon and nitrogen dynamics in a temperate steppe of northern China

We evaluated plant species effects on soil carbon (C) and nitrogen (N) dynamics in a steppe ecosystem of northern China. In two subsequent years, we measured soil properties in the top 10 cm of the soil under replicated mono-dominant plant patches in two sites that differed in land-use history: a cultivated site (old field) and an uncultivated site (steppe). Both in the cultivated site and the uncultivated site, we selected patches of three of the dominant plant species. Contrast analyses in ANOVA showed that soil organic carbon (SOC) and total N content (g per m2) was on average lower in the cultivated site than in the uncultivated site. On average, soil respiration was also lower in the cultivated site than in the uncultivated site. However, overall differences in soil C and N dynamics between the cultivated site and the uncultivated site (if existing) were generally small compared to the effects of individual plant species. Soil respiration differed among plant species in the cultivated site, but not in the uncultivated site. In contrast, SOC content, total N, and N mineralization rate differed among plant species in the uncultivated site, but not in the cultivated site. Mineralization and nitrification rates strongly varied among the dominant plant species, particularly in the uncultivated site. Variation in both C and N pools and fluxes could be best explained by a combination of plant biomass, litter, and soil microbial and micro-climatic parameters. Cultivation can directly affect soil C and N dynamics. However, importantly, our data suggest that indirect effects through changes in plant species composition are also important, and probably strongly interact with direct effects in affecting soil C and N dynamics after land-use change. Hence, evaluation of land-use history on soil C and N dynamics requires integral analyses of changes in plant community composition.

Diversity of culturable ericoid mycorrhizal fungi of Rhododendron decorum in Yunnan, China

The diversity of ericoid mycorrhizal fungi isolated from Rhododendron decorum Franch. in Yunnan, southwestern China, was examined for the first time. In total 300 hair-root samples were collected from 13 R. decorum individuals in two adjacent wild population sites and one cultivated population site. Two hundred eighteen slow-growing isolates were obtained; the ability of some to form ericoid mycorrhiza was tested in vitro. One hundred twenty-five isolates formed hyphal structures morphologically corresponding to ericoid mycorrhiza, and these were determined by morphological and molecular means to belong to 12 fungal species. There were hardly any differences in species among the three sampled populations. The sequences of several isolates were similar to those of Oidiodendron maius and ericoid mycorrhizal fungi from Helotiales, accounting respectively for 18.4% and 24.8% of the total culturable ericoid mycorrhizal fungi assemblage. Dark septate endophytes were detected in the sampled hair roots by microscopy.

Land use impacts on physical-based soil organic matter fractions on three hillside Ferrasols in Mexico

The effects of cultivation in hillside (> 30% slope) on soil C and N stocks after forest clearance and subsequent cultivation in new re-growth forest sites not always induce rapid soil organic matter (SOM) loss in subtropical areas. In the present study we evaluated the sensitivity to SOM changes of material floatable in water (Fw), coarse sand (> 250 im), fine sand (50-250 im), silt (2-50 im) and clay (0-2 im) fractions by the impact of cultivation of Mexican Ferrasols. This research also determined the relative degree of C and N saturation in the silt and clay size particles. The soil physical fractions were obtained after ultrasonic vibration and sedimentation. Soil organic matter stock (0-20 cm depth) in cultivated sites ranged from 54 to 146 Mg C ha-1 and from 3.9 to 7.1 Mg N ha-1 and in the forest soil 46-94 Mg C ha-1 and 3.7-5.1 Mg N ha-1. The relative distribution of C and N was lower in the coarse sand and highest in the silt fraction; the latter paralleled the changes of whole soil C and N. Coarse sand was the most sensitive fraction responding to cultivation, thus representing a diagnostic pool to assess the SOM shifts under cultivation. Half of our studied soil showed a low degree of C and N saturation in the silt and clay fraction indicating potential for accumulation of C and N, while the other half were well above the saturation limit.

Seasonality and management, not proximity to highway, affect species richness and community composition of epiphytic phylloplane fungi found on (wild and cultivated) Vaccinium spp.

The phylloplane is a cryptic environment that harbors a variety of pathogens and pathogen antagonists, and these populations are affected by many factors such as weather, season, plant location and leaf phenology. To address the hypothesis that pollution from a major highway would influence phylloplane communities, blueberry leaves were collected in Apr., Jun., Aug., and Oct. over 2 years from bushes in wild areas and cultivated farms along transects perpendicular to the Atlantic City Expressway. Community structure and species richness changed monthly, annually, and from site to site. Management practices in cultivated sites accounted for much of the variation in species richness and community composition among sites. Leaf age also influenced the community structure of phylloplane fungal communities. Leaves collected in Apr. had significantly lower species richness than those collected in later months (F = 19.37, P < 0.0001). Yearly differences in species richness and community structure were likely due to differences in meteorological variables.

Impacts of soil conservation on groundwater recharge in the semi-arid Loess Plateau, China

Soil conservation measures undertaken to address land degradation can alter the hydrologic cycle by changing partitioning of water fluxes at the land surface. While effects on runoff are well documented, impacts of soil conservation activities on fluxes to groundwater are poorly understood. The goal of this study was to examine fluxes to groundwater in a semi-arid area of China’s Loess Plateau that has been subject to extensive soil conservation activities. Unsaturated zone pore-water pressures and concentrations of chloride show that impacts on deep drainage differ between ecological and structural soil conservation approaches. High matric potentials and low chloride beneath cultivated terrace and gulley sites are consistent with deep drainage occurring at these sites. Estimated recharge rates for dryland cultivated upland sites were approximately 55–90 mm/year (11–18% of mean annual rainfall) based upon chloride mass balance. In contrast, results suggest that mature tree and shrub plantations prevent deep drainage. Stable isotope signatures of unsaturated-zone moisture and groundwater indicate that focused infiltration through gullies and other topographic lows is likely to be the primary recharge mechanism. The results of this study highlight the potential for inadvertent effects of some soil conservation approaches on regional water resources.

Arbuscular mycorrhizal fungi associated with Artemisia umbelliformis Lam, an endangered aromatic species in Southern French Alps, influence plant P and essential oil contents

Root colonization by arbuscular mycorrhizal (AM) fungi of Artemisia umbelliformis, investigated in natural and cultivated sites in the Southern Alps of France, showed typical structures (arbuscules, vesicles, hyphae) as well as spores and mycelia in its rhizosphere. Several native AM fungi belonging to different Glomeromycota genera were identified as colonizers of A. umbelliformis roots, including Glomus tenue, Glomus intraradices, G. claroideum/etunicatum and a new Acaulospora species. The use of the highly mycorrhizal species Trifolium pratense as a companion plant impacted positively on mycorrhizal colonization of A. umbelliformis under greenhouse conditions. The symbiotic performance of an alpine microbial community including native AM fungi used as inoculum on A. umbelliformis was evaluated in greenhouse conditions by comparison with mycorrhizal responses of two other alpine Artemisia species, Artemisia glacialis and Artemisia genipi Weber. Contrary to A. genipi Weber, both A. umbelliformis and A. glacialis showed a significant increase of P concentration in shoots. Volatile components were analyzed by GC-MS in shoots of A. umbelliformis 6months after inoculation. The alpine microbial inoculum increased significantly the percentage of E-β-ocimene and reduced those of E-2-decenal and (E,E)-2-4-decadienal indicating an influence of alpine microbial inoculum on essential oil production. This work provides practical indications for the use of native AM fungi for A. umbelliformis field culture.

Does cultivation influence the content and pattern of soil proteins?

Proteins comprise one of the largest N inputs to soils. There is, therefore, a need to investigate the factors involved in the inputs and fate of proteins in soil. While land use management is expected to influence the amount and diversity of soil proteins, the responses of protein as a source of mineralizable N to land use changes have not yet been studied. We hypothesized that extractable soil protein could be a sensitive indicator in evaluating the effect of stress in ecosystem. Soil samples were collected in October of 2009 from a native forest (Typic Calcixerolls) and a native rangeland (Typic Calcixerepts) as well as adjacent cultivated fields in Zagros area, central Iran. Tris–HCl buffer (pH 6.8) containing 1% (w/v) SDS was used for soil protein extraction. The results showed that soil protein content decreased by 64% and 55% in cultivated sites, as compared with their corresponding native forest and native rangeland sites, respectively. To determine the effects of land use changes on soil protein pattern, SDS-PAGE was carried out. Electrophoretic patterns of soil proteins from agricultural soils were clearly different from those of native lands. Protein bands ranged from 17 to 90kDa and from 20 to 62kDa in native forest and in the adjacent cultivated soils, respectively. Protein bands were detected in the range of 17–57kDa for the native rangeland soil but in the range of 17–198kDa for the adjacent cultivated soil. Land use changes were found not only to decrease significantly the amount of soil proteins but also to influence the protein pattern. We achieved the objective of this paper which was to show the potential of the quantity and diversity of soil proteins as indicators of land use changes. The presented soil protein extraction method as well as soil protein content and pattern determination require further validation in a variety of soils types, climates and land use systems.

FEEECT OF DIFFERENT IRRIGATION METHODS IN SOME MORPHOLOGICAL AND PHYSICAL PROPERTIES OF AN GYPSIFEROUS SOIL AT AL-THIRTHAR AREA

This study was conducted at fields of Al-Majd agricultural company which located between falluga and thirthar at al saqlawia / Al-Anbar government, to study the effect of using different irrigation methods (flood - drip - sprinkler) irrigation to using its gypsiferous soils with irrigation water class C3S1, to know the effect of this irrigation methods in some soil morphological and physical properties . After semi detail survey, four positions were pointed that were different in agricultural using nature for three years as following:P1 virgin soil (B), P2 land which used for cereals with flood irrigation method (FW3), P3 land which used for cereals with sprinkler irrigation method (SW3) and P4 land which used for vegetable with drip irrigation method (DV3).These four pedons were described morphologically then soil samples were taken from each horizon to analysis some physical properties. The results showed that following: 1. The thickness of surface horizons for cultivated site increased in comparison with uncultivated soil from 18cm to 25 cm. 2. The soil structure grade was weak in all pedon’s , especially at soil which was under the flood irrigation 3. There is no significant effect for irrigation method on particle density at all horizons, this property data was showed decreasing in its value with increasing soil content of gypsum, but the bulk density was effected by irrigation practice significantly, it was increased 5.4%, 10.0% and 13.9%as mean for treatments DV3, SW3 and FW3 respectively. 4. There is significant effect for irrigation method on studied soil water properties (field capacity, wilting point and available water).Using of drip irrigation method was showed higher increasing in these properties in comparison with other irrigation methods. 5. Soil penetration resistance was decreased 3.9% in farming lands without significant different in comparison with virgin land, and lower value was pointed at Ap horizon for DV3 treatment reached 2.6 kg.cm-2 while the same horizon for SW3 treatment was showed the higher value 3.1 kg.cm-2.

Soil chemical properties under modern and traditional farming systems at Khagrachari, Chittagong Hill Tracts, Bangladesh

Land degradation in Chittagong hill tracts has been taking place due to shrinkage of forest cover, policy weakness, population explosion, and inappropriate hill farming system. Modern farming system in the Chittagong hill tracts like Sloping Agricultural Land Technology (SALT) is practiced to provide a new strategy for developing lands for economic productivity and bio-diversity conservation through establishment of ecological community rather than traditional shifting cultivation which is no longer sustainable according to the carrying capacity of ecosystem of Chittagong hill tracts. This study is to find out changing trends of soil chemical properties of sites under modern and traditional farming systems at Khagrachari district of Chittagong hill tracts. The result of the research shows that Sloping Agricultural Land Technology has significantly higher capacity of production due to the presence of the highest percentage of organic carbon, organic matter, compared with shifting cultivated site. The study recommends that shifting cultivation may be changed into a relatively stable semi-permanent farming system through developing participatory integrated farming systems to establish stable production environment in the Chittagong Hill Tracts.

Study of antimony (III) binding to soil humic acid from an antimony smelting site

Soil samples were collected from an antimony smelting site in Guangxi Zhuang Autonomous Region, China, at four locations characterized by different land usage, including two cultivated sites: one formerly cultivated and one uncultivated. Surface soils from all four sites were heavily polluted by toxic metals including antimony (Sb), lead (Pb) and arsenic (As), and their concentrations were 410–3330mg·kg−1, 410–3690mg·kg−1 and 200–460mg·kg−1, respectively. In the uncultivated area metal levels were 1.4–6.2 times higher as compared to the formerly and currently agriculture land. Lower levels at the cultivated sites may have resulted from an accumulation of airborne particles by vegetation and lower contents in the surface soil. However, the elevated mercury (Hg) content may reflect both natural and anthropogenic origins in this smelting site. Soil-derived humic acid (HA) from the smelting site reacted directly with Sb (III) aqueous solutions with concentrations of 12, 71 and 143mg·g−1. The maximum Sb (III) binding to the soil-derived HA was 253μmol·g−1 (added concentration of 71mg·g−1) and showed more binding (up to 50%) at lower Sb content.

First use of the 137Cs technique in Nigeria for estimating medium-term soil redistribution rates on cultivated farmland

Abstract Soil erosion is a serious problem in the forest-savanna transition zone or derived savanna of West Africa and Nigeria and needs to be reduced to maintain soil quality and to ensure food security. In 2007, the use of the fallout radionuclide 137 Cs as a tracer for estimating the magnitude of medium-term (40–50 years) rates of soil redistribution was tested at a research station in Ibadan, Nigeria, to investigate, for the first time, its applicability in the derived savanna of West Africa. Because of the traditional tillage practice for cassava cultivation of creating downslope oriented ridges and furrows during the annual ploughing, there was a need to adapt the 137 Cs approach to these specific condition. The mean inventory was determined for cores collected from both ridges and furrows at different positions down the slope and this value was used to estimate the downslope variation in the longer term soil redistribution rate. The mean 137 Cs reference inventory obtained for an undisturbed site was 568 ± 138 Bq m −2 . The average inventory for the upper slope of the cassava field (423 ± 323 Bq m −2 ) was generally lower than the average inventory for the middle slope (509 ± 166 Bq m −2 ) and for the lower slope (606 ± 245 Bq m −2 ) and these results provided clear evidence of the downslope movement of soil. The mean 137 Cs inventory for the study area within the cassava field (496 ± 273 Bq m −2 ) was 13% lower than the reference inventory, indicating that some of the soil mobilised and redistributed by erosion had been exported beyond the field. Using 137 Cs data set and the conversion model mass balance model 2 (MBM2), the gross erosion rate from the cultivated site was estimated to be 18.3 t ha −1 year −1 and the net erosion rate 14.4 t ha −1 year −1 , providing a sediment delivery ratio of 78%. These estimates are comparable to the rates generated by conventional soil loss measurements made close to the study site. The study demonstrates that the 137 Cs technique can be successfully used to obtain data on medium-term soil redistribution in the derived savanna of Nigeria, and that it could be a useful tool for supporting the improvement of soil conservation on farmland in West Africa.

DROUGHT SENSITIVITY OF CASTANEA SATIVA: CASE STUDY OF SUMMER 2003 IN THE SOUTHERN ALPS

The post-cultural dynamics of abandoned chestnut stands and diseases, such as chestnut blight and ink-disease, have been recognized as major drivers of the natural withdrawal of the chestnut tree. Climate warming causing drought might interact with these dynamics and accelerate the disappearing of the chestnut tree from former cultivated sites. The summer of 2003 was by far the hottest on record in Switzerland. Several chestnut stands were damaged by a combination of the heat and a significant precipitation shortfall in the Southern Alps. Between August and October 2003, these areas were mapped and examined for possible correlations with the geomorphologic site conditions. As expected, the drought and heat especially impacted stands in unfavourable settings with shallow soil and on forest edges. Forest edge effects seem to be even more relevant as the exposure. Although damage remained within limits, the 2003 summer drought showed that Castanea sativa does not have an effective mechanism to protect itself against over-transpiration in extremely hot and dry weather. This may raise new questions about the ecological plasticity of the chestnut tree in view of possible climate changes.

Sediment, nutrient and water losses by water erosion under agroforestry systems in the semi-arid region in northeastern Brazil

Inadequate soil management practices adopted in the Brazilian semi-arid region contribute to erosive processes. Agroforestry systems (AFs) have been considered an alternative to reduce water erosion. This study aimed to evaluate the impact of two alternatives AFs, a traditional and an intensive cropping system on the losses of sediments, water, organic carbon and nutrients caused by water erosion in comparison to the natural vegetation (caatinga) in a semi-arid region of northeastern Brazil. The agroecosystems studied were: agrosilvopasture (AGP) which consisted of an alley cropping system, cultivated with Leucaena leucocephala and maize, within an area composed by 22% of native trees (200 native trees per hectare) which was grazed during the dry season; silvopasture (SILV) that was composed by 38% of native trees (260 trees per hectare) with a stocking rate of 20 ewes during whole year; traditional agrosilvopasture (TRAG) being managed as following: total deforestation, burning of the residues, cropped with maize for 2 years (1998 and 1999) and fallow during 8–10 years; and intensive cropping (IC) system which was deforested and burned in 1997 followed by cultivation of maize from 1998 to 2002, and thereafter by a fallow period of 8–10 years similar to TRAG. Two areas of native forest (NF1, NF2) known as ‘caatinga’, used as grassland during the dry season and as a source of wood, were selected and used as reference of steady state in the comparative study in relation to the cultivated sites. Sediment and water losses as a result of erosion were collected during two rainy seasons, i.e. 2003 and 2004, and nutrients and organic carbon contents were determined. Soil samples were collected and organic carbon, pH in water, pH in KCl, water dispersible clay (WDC) and hydraulic conductivity (K0) were measured. In 2003, sediment and water losses did not differ significantly among all treatments. However, in 2004, TRAG (0.70 Mg ha−1) and NF1 (1.37 Mg ha−1) showed the highest sediment losses, whereas TRAG and IC presented the highest water losses. On average, nutrients losses in cropped areas were lower than in natural vegetation (NF1, NF2). The alternative AFs (AGP, SILV) were efficient to reduce water erosion effects when compared to the most common agricultural practices adopted in the region, being highly recommended as sustainable technical alternatives for food production in the region.

Surface-active arthropods in organic vineyards, integrated vineyards and natural habitat in the Cape Floristic Region

The Cape Floristic Region (CFR), South Africa, is a biodiversity hotspot challenged by intensive wine production. Innovative approaches are being explored to optimize wine production without compromising biodiversity. As organic farming enhances biodiversity conservation in many other regions, the aim here was to assess the potential of organic vineyard management for conserving CFR soil surface arthropod diversity. Pitfall traps were used to sample arthropods in three study areas, each of which included an organic vineyard, an integrated vineyard and a natural vegetation reference habitat. Overall arthropod morphospecies richness was highest in natural sites, followed by organic vineyards and then integrated vineyards. The same trend was seen for predators, saprophages and phytophages. The ability of organic vineyards to sustain more morphospecies than integrated vineyards were partially due to higher non-crop vegetation complexity and less intense management in the organic vineyards. Arthropod assemblages were similar in organic and integrated vineyards, while both land-uses differed greatly from natural sites. Variation among natural vegetation assemblages in different study areas was also much greater than among assemblages of cultivated sites. Organic vineyard management has the potential to make an important contribution to arthropod conservation in the CFR at the field scale. However, at the landscape scale, natural habitat supports a much wider variety of morphospecies, and the preservation of natural fragments in the vineyard landscape may be the most effective measure to increase biodiversity in the winelands.

Effects of Agricultural Management, Land Use, and Watershed Scale on E. coli Concentrations in Runoff and Streamflow

Fecal contamination of surface waters is a critical water quality concern with serious human health implications. Many states use Escherichia coli as an indicator organism for fecal contamination and apply watershed models to develop and support bacterial Total Maximum Daily Loads (TMDLs); however, model applicability is greatly restricted due to the sparse availability of E. coli data for validation and calibration at various scales. Similarly, watershed-scale information on the effects of management practices and land use on E. coli fate and transport is limited. Thus, this study was designed to measure E. coli concentrations in edge-of-field runoff and in streams with various agricultural management practices, land uses, and watershed scales. Results showed that application of dairy compost to pasture, cultivated, and mixed land use sites did not significantly affect E. coli concentrations in runoff at the field scale. In contrast, grazed sites had significantly higher runoff E. coli concentrations than cultivated sites, but the increase cannot be attributed solely to grazing cattle. No significant differences in E. coli concentrations were determined for presumably impacted and unimpacted rural streams with differing anthropogenic inputs, which highlights the challenges of managing and regulating bacterial contamination. The results also showed that E. coli concentrations consistently decreased as watershed scale increased from field to small watershed to river basin scale. Results from this study highlight the importance of considering all potential sources (including animal feeding operations, wastewater treatment plants and on-site systems, cultivated and pasture fields, wildlife, and streambed resuspension) to properly assess E. coli contamination in rural watersheds. Results also demonstrated the need for an improved basic scientific understanding of fecal bacteria in the environment to reduce the substantial uncertainty associated with assessing, modeling, managing, and regulating bacterial contamination.

Uncertainty in future soil carbon trends at a central U.S. site under an ensemble of GCM scenario climates

This study uses DAYCENT model to investigate the sensitivity of soil organic carbon (SOC) at an intensely cultivated site in the U.S. Midwest under an ensemble of scenario climates predicted by IPCC models. The model ensemble includes three IPCC models (Canadian, French, German), three emission scenarios (B1, A1B, A2) and three time periods (late 20th, mid-21st, late 21st century). DAYCENT shows that SOC at the site would decline by 0.3–2.6 kg m −2 (5–35%) depending on the models and scenarios from late 20th to mid-21st century despite a larger increase of future net primary production (NPP) than respiration. The future SOC decrease is mostly attributable to harvest loss. The wide spread in future SOC decline rates are in part because SOC decrease (by respiration) is directly proportional to SOC itself. Any uncertainty in absolute SOC in DAYCENT would translate directly into its trend, unlike other variables such as temperature whose trends are independent of their values themselves, contrasting the reliability of SOC trend with temperature change.

Aluminium release from acidic forest soil following deforestation and maize cultivation in Ghana, West Africa

Acidic tropical soils often have high Al3+ concentrations in soil solutions, which can be toxic to plants and, thereby, reduce agricultural yields. This study focuses on the impact of deforestation and cultivation on the short and long-term Al geochemistry of acidic soils in Ghana, West Africa. Site-specific investigations were made at two sites covered with forest and one site cultivated with maize (Zea mays L.). The capacity of soil to resist acidification was investigated in a leaching experiment and the corresponding release of aluminium quantified. Field results revealed a significant aacidification and Al mobility in the root zone of the cultivated site as compared to the forest sites. The leaching experiment showed that further acidification would significantly enhance Al-release and, consequently, the presence of Al3+ in soil solution. It is concluded that deforestation and cultivation in the study area has resulted in increasing levels of Al3+ and a lowering of the soils capacity to resists further acidification. This may be critical in relation to land-use management and long-term agricultural productions.

Estimation of total erosion in cultivated Black soils in northeast China from vertical profiles of soil organic carbon

SummaryIt is difficult to estimate soil thickness eroded from annual erosion rates in cultivated Black soils in northeast China because of the uncertainty of the time when the soil was first cultivated for agricultural crops. Assuming soil organic carbon (SOC) profile curves for cultivated sites are the same as virgin sites before cultivation, it may be possible to estimate the total thickness of surface soils lost by erosion by vertical movement of plotted SOC profiles until those for the virgin and cultivated soils are superimposed. We collected pairs of soil samples (0–1 m) with one sample in each pair from a virgin site and the other from a nearby cultivated site in Heilongjiang province, northeast China. In undulating areas where soil erosion was moderate, the shapes of SOC distribution curves below 40 cm depth were nearly identical for both cultivated and virgin soils, but were offset vertically. This offset was attributed to the loss of surface soil by erosion in the cultivated land. By moving the distribution curve of SOC in cultivated soil downwards by 12.7 cm, we found nearly coincident curves below 45 cm for the virgin and cultivated soils. This thickness (12.7 cm) was believed to be the depth of soils that had been eroded since the onset of cultivation in Black soils in northeast China. We concluded that the amount of surface soil lost by erosion could be estimated from comparison of the vertical distribution of SOC in cultivated and virgin soils.