Statistical analyses and controls of root-zone soil moisture in a large gully of the Loess Plateau

Soil moisture variability and controls are little known in large gullies of the Loess Plateau which represent complex topography with steep slopes. This study analyzed spatial–temporal variability of soil moisture at the 0–20, 20–40, 40–60, and 60–80 cm depths in a large gully of the Loess Plateau based on root-zone soil moisture measurements for 3 years (2009–2011). The result showed that mean soil moisture, standard deviation (SD), and coefficient of variation, were highly dependent on depth; the highest mean value was observed at the 20–40 cm depth, while the lowest one was at the 0–20 cm depth. The SD increased with mean soil moisture for various depths as soil moisture was relatively wet; however, a transition that SD decreased with mean soil moisture occurred when soil moisture was relatively dry. Positive correlations exist between moisture contents over different depths, and that the relationships of the neighboring layers are relatively high with R ² from 0.70 to 0.76. Correlation analysis, principle component analysis, and stepwise multiple regression analysis showed that soil particle size distribution and topography (slope and elevation) were the main environmental factors controlling soil moisture variability in the large gully.     

Accumulation behavior of toxic elements in the soil and plant from Xinzhuangzi reclaimed mining areas,China

The concentration and distribution characteristics of toxic elements in soil and plant were investigated in the coal refuse reclaimed areas of Huainan, China. Ninety soil samples from different depth (0–20, 20–40, 40–60 cm) and 120 plant samples were collected based on grid sampling method. The concentrations of the selected toxic elements (As, Cd, Cu, Ni, Pb and Zn) in the soil and plant samples were determined by using inductively coupled plasma mass spectrometry. The elevated concentrations of toxic elements in the soils at the depth of 20–40 and 40–60 cm suggested that the coal refuse reclamation may lead to potential environmental impacts. The toxic element tolerance could be observed in all the selected plant samples. The concentrations of toxic elements in the underground tissues were higher than that of aboveground tissues. Conclusively, the present study provided a comprehensive evaluation of soil and plant toxic element implications from coal refuse reclaimed areas in China and was also helpful for environmental protection and monitoring the safety of plant.     

Spatial heterogeneity of soil organic matter and soil total nitrogen in a Mollisol watershed of Northeast China

The spatial heterogeneity of soil nutrients influences crop yield and the environment. Previous research has focused mainly on the surface layer, with little research being carried out on the deep soil layers, where high root density is highly related to crop growth. In the study, 610 soil samples were collected from 122 soil profiles (0–60 cm) in a random-sample method. Both geostatistics and traditional statistics were used to describe the spatial variability of soil organic matter (SOM) and total nitrogen (TN) deeper in the soil profile (0–60 cm) with high root density from a typical Mollisol watershed of Northeast China. Also, the SOM and TN in farmland and forest (field returned to forest over 10 years) areas was compared. The spatial autocorrelations of SOM at 0–50 cm depth and TN at 30–60 cm depth were strong, and were mainly influenced by structural factors. Compared to farmland, SOM and TN were typically lower in the 0–30 cm depth of the forest areas, while they were higher in the 30–60 cm depth. As well, both SOM and TN decreased from the 0–20 cm layer to the 30–40 cm layer, and then discontinues, while they continuously decreased with increasing soil depth in the farmland. SOM and TN were typically higher at the gently sloped summit of the watershed and part of the bottom of the slope than at mid-slope positions at the 0–30 cm depth. SOM and TN were lower on the back slope at the 30–60 cm depth, but were higher at the bottom of the slope. Also, the spatial distribution of the carbon storage and nitrogen storage were all highest at the bottom of the slope and part of the summit, while they were lowest in most of back slope in depth of 0–60 cm, and mainly caused by soil loss and deposition. SOM at 0–60 cm and TN at 0–40 cm greater than the sufficiency level for crop growth (3.7–79.2 and 0.09–3.09 g kg^?1, respectively) covered 99 % of the total area, yet for TN, over 35 % of the total area was less than the insufficiency level at the 40–60 cm depth. Generally, accurately predicting SOM and TN is nearly impossible when based only on soil loss by water, although the fact that variability is influenced by elevation, soil loss, deposition and steepness, was shown in this research. Nitrogen fertilizer and manure application were needed, especially in conjunction with conservation tillage in special conditions and specific areas such as the back slope, where soil loss was severe and the deep soil that lacked TN was exposed at the surface.     

Variations in soil characteristics among urban green spaces in Kumasi,Ghana

Urban soils, although crucial to defining urban vegetation types and strengthening the resilience of urban ecosystems, can be severely modified by human activities. Yet understanding of these modifications and their implications for soil properties is limited. This study examined the vertical and spatial variability of selected soil physicochemical properties (pH, SOM, OC, TN, and bulk density) in Kumasi, Ghana, using a stratified random sampling technique. Soil samples were collected at three depths (0–15, 15–30, and 30–60 cm) from 161 plots in eight green space types within two urban zones. Mean topsoil pH ranged between 5.0 in the natural forest and 6.5 in home gardens. Mean bulk density, nitrogen, and carbon concentrations differed among green space types and depths (p?<?0.0001). Soil nitrogen and carbon concentrations in the 0–15 cm depth were two times greater than those of the 30–60 cm depth. Soil pH and organic matter concentrations were higher in the core urban soils than in the peri-urban while the reverse was true for total soil N and bulk density. Canonical discriminant analysis showed considerable separation of green space types based on the soil physicochemical properties. Higher total nitrogen and C:N ratios separated natural forest and cemetery from the other UGS types, whereas higher pH and bulk densities separated plantations and home gardens from the rest of the UGS types. Furthermore, the subsoil layers were laden with undecomposed cloths, plastics, concrete, and metal parts which can obstruct root growth and water movement. Results generally demonstrate considerable variability in soil properties among urban green spaces and highlight the need for a better understanding of these patterns to ensure continued support for plant growth, green space sustenance and maintenance, and the ecosystem services derived from them.     

环渤海低平原水土盐分与水位埋深的空间变异及协同克立格估值

针对环渤海低平原水土盐分和水位埋深,通过选取0～20cm深度内的127个代表性土样进行土壤全盐量测定,并对130个水井的水位埋深及128个地下水样的矿化度进行测定.综合运用普通克立格(OrdinaryKriging)与协同克立格(CoKriging)方法与GIS技术研究水土盐分及水位埋深的空间分布状况.结果表明,土壤盐...     

Land degradation risk assessment in Al-Sawda terraces,Kingdom of Saudi Arabia

Monitoring of soil properties is a significant process and plays an important role about how it can be used sustainably. This study was performed in a local area in Sawda Mountains KSA to map out some soil properties and assess their variability within the area under different land cover. Soil sampling was carried out in four different sites using the grid sampling technique. Ten samples were collected in each location within a 10 by 10 km area; soil was sampled at 0–30-cm depth. The soil samples were air-dried, crushed, and passed through a 2-mm sieve before analyzing it for pH, EC, CaCO₃, organic matter contents, and bulk density. The thematic maps of these characteristics were produced using ArcGIS 10.0 software. Finally, the land degradation was assessed using three factors: soil salinization, compaction, and edibility. The obtained results showed that the high risk of soil compaction, salinization, and erodibility occupied an area 5.6 ha (17.5%), 3.7 ha (11.54%), and 8.1 ha (25.3%), respectively, in the surface soil layer. The land degradation risk in the study area due to salinization was low to high; however, the degree of soil compaction was moderate to very high. The K-factor (soil erodibility) in the area ranged between 0.1 and 0.35 Mg h MJ^?1 mm^?1, and most of the study area was located in moderate to high erodibility classes.     

Spatial variability of soil moisture at typical alpine meadow and steppe sites in the Qinghai-Tibetan Plateau permafrost region

Permafrost degradation has the potential to significantly change soil moisture. The objective of this study was to assess the variability of soil moisture in a permafrost region using geostatistical techniques. The experiment was conducted in August 2008 in alpine steppe and meadow located in the Qinghai-Tibetan Plateau permafrost region. Four soil depths (0–10, 10–20, 20–30 and 30–40 cm) were analyzed using frequency domain reflectometry, and sampling made of 80 points in a 10 m × 10 m grid were sampled. Soil moisture was analyzed using classical statistics to appropriately describe central tendency and dispersion, and then using geostatistics to describe spatial variability. Classical statistical method indicated that soil moisture in the permafrost region had a normal distribution pattern. Mean surface soil moisture in alpine meadow was higher than that in alpine steppe. The semivariograms showed that soil moisture variability in alpine cold steppe was larger than that in alpine meadow, which decreased with depths. Nugget values in alpine steppe were low (0.1–4.5), in contrast to alpine cold meadow. Soil moisture in alpine steppe had highly structured spatial variability with more than 93.4% spatial heterogeneity, and the range decreased with depth. Soil moisture content in alpine cold meadow had a moderate spatial dependence with a range of 51.3–169.2 m, increasing with depth.     

Investigation of spatial variability and pattern analysis of soil properties in the northwest of Iran

Analysis of the spatial variability of soil properties is important to explain the site-specific ecosystems. Spatial patterns of some soil properties such as soil texture, exchangeable sodium percentage (ESP), electrical conductivity (ECe), soil pH and cation exchange capacity (CEC) were analyzed in salt and sodic affected soils in the south of the Ardabil province, in the northwest of Iran, to identify their spatial distribution for performance of a site-specific management. Soil samples were collected from 0 to 30, 30 to 60, 60 to 90, 90 to 120 and 120 to 150 cm soil depths at sampling sites. Data were investigated both statistically and geostatistically on the basis of the semivariogram. The spatial distribution model and spatial dependence level varied in the study area. Among the considered parameters, maximum and minimum spatial variability were observed in EC and pH parameters, respectively. Soil properties showed moderate to strong spatial dependence, except for a few. ECe was strongly spatially dependent in the total soil depth and clay was strongly spatially dependent at the first depth. Sand and pH were moderately spatially dependent for three of the five depths. ESP was strongly spatially dependent and silt was moderate in the total soil depths, except at 90–120 cm depth. Furthermore, CEC had strong spatial dependence for three of the five depths. All geostatistical range values were >1,389 m in this study. It was concluded that the strong spatial dependency of soil properties would lead to extrinsic factors such as bedrock, agricultural pollution, drainage and ground water level.     

Spatial and seasonal distributions of soil phosphorus in a typical seasonal flooding wetland of the Yellow River Delta,China

Soil samples from 0 to 100 cm depth were collected in four sampling sites (Sites A, B, C and D) along a 250-m length of sampling zone from the Yellow River channel to a tidal creek in a seasonal flooding wetland of the Yellow River Delta of China in fall of 2007 and spring of 2008 to investigate spatial and seasonal distribution patterns of total phosphorous (TP) and available phosphorus (AP) and their influencing factors. Our results showed that TP contents in spring and AP contents in both seasons in surface soils increased with increasing distances away from the Yellow River channel. TP contents in surface soils (0–10 cm) followed the order Site A (698.6 mg/kg) > Site B (688.0 mg/kg) > Site C (638.8 mg/kg) > Site D (599.2 mg/kg) in fall, while Site C (699.6 mg/kg) > Site D (651.7 mg/kg) > Site B (593.6 mg/kg) > Site A (577.5 mg/kg) in spring. Generally, lower TP content (630.6 mg/kg) and higher AP level (6.2 mg/kg) in surface soils were observed in spring compared to fall (656.2 mg/kg for TP and 5.2 mg/kg for AP). Both TP and AP exhibited similar profile distribution patterns and decreased with depth along soil profiles with one or two accumulation peaks at the depth of 40–80 cm. Although the mean TP content in soil profiles was slightly higher in spring (635.7 mg/kg) than that in fall (628.0 mg/kg), the mean TP stock was obviously lower in spring (959.9 g/m²) with an obvious accumulation at the 60–80 cm soil depth compared to fall (1124.6 g/m²). Topsoil concentration factors also indicated that TP and AP had shallower distribution in soil profiles. Correlation analysis showed that AP had significant and positive correlation with these soil properties such as soil organic matter, salinity, total nitrogen and Al (p < 0.01), but TP was just significantly correlated with TN and Al (p < 0.05).     

Spatial variability of soil available phosphorus in a typical watershed in the source area of the middle Dan River,China

Phosphorus is an essential and common limiting element for plants. Phosphorus losses from agricultural production systems are known to contribute to accelerated eutrophication of natural waters. In this study, soil available phosphorus (SAP) content and SAP density were estimated based on a soil survey of a small watershed in the Dan River, China, and the spatial heterogeneity of SAP distribution and the impacts of land-use types, elevation, slope and aspect on SAP were assessed. Field sampling was carried out based on a 100 m × 100 m grid system overlaid on the topographic map of the study area, and samples were collected in three soil layers to a depth of 40 cm. A total of 190 sites were sampled, and 539 soil samples were collected. The results showed that classical kriging could successfully interpolate SAP content in the watershed. SAP content showed a downward trend with the increase in soil depth and the extent of SAP variability in the three soil layer is moderate. There were significant differences among the three soil layers (P < 0.01). The land use had a great impact on the SAP content. ANOVA indicated that the spatial variation of SAP contents under different land-use types was significant (P < 0.01). The SAP density of different land-use types followed the order of cropland > forestland > grassland. The mean SAP density of cropland, forestland and grassland at a depth of 0–40 cm was 4.28, 3.74 and 2.81 g/m², respectively. SAP and topographic factors showed that SAP content increased with decreasing altitude and slope gradient. The soil bulk density played a very important role in the assessment of SAP density. In conclusion, the soils in the source area of the middle Dan River would reduce SAP with conversions from cropland to forest or grassland.     

Soil properties as indicators of desertification in an alpine meadow ecosystem of the Qinghai–Tibet Plateau, China

The objective of this study was to examine the variation of time and space and the effects of alpine meadow desertification, and the study area was selected at the Qinghai–Tibet Plateau of China. The sampling locations were categorized as the top, middle, bottom of the slope and flat in front of the slope, and the sites were classified as alpine meadow, light desertified land, moderate desertified land, serious desertified land, and very serious desertified land according to the level of alpine meadow desertification. This study examined spatial and temporal variability in soil organic carbon (SOC), total nitrogen (TN), pH, and soil bulk density due to wind erosion and documents the relationship between soil properties and desertification of alpine meadows. Desertification caused decreases to soil organic carbon and total nitrogen and increases to pH and soil bulk density. Soil properties were greatly affected by the level of alpine meadow desertification with the changes being attributed to overgrazing. The middle portion of slopes was identified as being the most susceptible to desertification. Carbon and nitrogen stocks were found to decrease as desertification progressed, the SOC stocks were 274.70, 273.81, 285.26, 196.20, and 144.36 g m^?2 in the alpine meadow, light desertified land, moderate desertified land, serious desertified land and very serious desertified land, respectively; and the TN stocks were 27.23, 27.11, 28.35, 20.97, and 17.09 g m^?2 at the top 30 cm soil layer, respectively. To alleviate desertification of alpine meadow, conservative grazing practices should be implemented.     

Effects of tilling methods on soil penetration resistance,organic carbon and water stable aggregates in a vineyard of semiarid Mediterranean environment

Tillage, especially in semiarid Mediterranean environment, enhances the mineralization process of soil organic matter (SOM) and, in turn, decreases aggregate stability. Furthermore, continuous tillage leads to the formation of plough pan beneath the tilled layer. In the present study, we investigated the effect of an innovative self-propelled machine (spading machine, SM) for shallow tillage on SOM, water stable aggregates (WSA) and soil penetration resistance (PR). Such effects were compared to those of chisel plough (CP), rotary tiller (RT) and no tillage (NT). Each tilling method was applied up to a depth of 15 cm, whereas in NT only a brush cutter was used for weed control. Soil analyses were performed at the start of the experiment (March 2009, T0), in April 2010 (T1), May 2012 (T3), and June 2014 (T5) at both 0–15 and 15–30 cm. Compared to T0, soil PR increased with time in all the treatments and generally followed the order SM?<?RT?<?CP?<?NT. In soil tilled with the SM, soil PR never exceeded 2.5 MPa that was demonstrated to be a critical value for root elongation, and no evidence of the formation of plough pan beneath the tilled layer was observed. SOC as well as water content and WSA were higher in SM compared with CP and RT. In conclusion, the spading machine was proved to be more efficient in lowering the soil PR and in avoiding the formation of the plough pan. Furthermore, SM increased SOC and WSA.     

Geochemical studies on urban soil from two sampling depths in Tampere Central Region,Finland

Preliminary geochemical mapping was carried out within urban areas in Tampere Central Region, Finland, to gain a better understanding of element concentrations in urban soil and to provide information on baselines in soil within urban centres for soil contamination assessment purposes. The soil samples were taken from central city parks, day-care centres and school yards, and residential areas. Various sampling depths have generally been used in urban geochemical surveys. The aim of this study was to compare the results from two commonly used sample types taken from the same sites in urban soil: single samples of minerogenic topsoil from the 0–25 cm layer and composite samples of minerogenic topsoil from a depth of 0–2 cm. The concentrations of most of the studied trace elements showed a significant correlation between samples from 0 to 2 and 0 to 25 cm, but element concentrations differed between the two studied sample depths. For most of the studied elements, the median concentrations were higher in the 0–25 cm samples, but anomalous concentrations were more often found in the 0–2 cm samples. Some elements had elevated concentrations when compared with the Finnish guideline values for soil contamination assessment. This study did not conclusively establish whether a sampling depth of 0–2 or 0–25 cm should be recommended for similar studies in the future. Selection of the sampling depth in geochemical studies greatly depends on the aim of the project. In order to determine the upper limits of geochemical baseline variation, the deeper sampling depth appears to be more feasible. However, for the preliminary health risk assessment of areas with sensitive land uses, e.g. children’s playgrounds, samples from 0–2 cm depth are considered informative. Such samples may also be used to indicate local sources of dusting creating site-specific hotspots of potentially harmful elements in urban topsoil.     

黄土丘陵小流域地形和土地利用对土壤水分时空格局的影响

采用1982～1985年和2002年两个时段的定点观测数据,系统分析了小流域尺度地形和土地利用类型对土壤水分时空格局的影响.结果表明:1)土壤水分变化特征为所有年份农地土壤水分都最大,灌木林地和荒草地较低,林地居中;不同坡向间以阴坡土壤水分最大;而不同坡位间以坡中部土壤水分最大.受降雨和植被耗水的影响,所有土地利用类型中土壤水分在整个生长期表现为降低型.2)在年尺度上表现为干旱年份土地利用类型和坡向对土壤水分的影响较大;而在湿润年份,其影响程度减弱;坡位在干旱和湿润年份对土壤水分的影响都较小.湿润年份,降雨量的增大弱化了地形和土地利用类型对土壤水分时空格局的影响;而干旱年份正好相反.3)在季节尺度上表现为在生长季节的中后期,土壤水分的变异格局主要受坡向影响;而在生长季节的中期,主要受土地利用类型影响;坡位在整个观测时段内影响都较小.4)在不同土壤层次方面特征为土地利用类型对0～20em层次影响较小,而对其他4个深度较大的层次(20～100cm)影响较大,并且5个层次中以40～60cm层次的差异最大;坡向对5个层次土壤水分的变异格局均有明显影响,并呈现随着深度的增加,其影响减弱的趋势;坡位对5个层次的土壤水分变异格局影响均较小.     

Estimation of soil organic carbon storage and its fractions in a small karst watershed

With few available soil organic carbon (SOC) profiles and the heterogeneity of those that do exist, the estimation of SOC pools in karst areas is highly uncertain. Based on the spatial heterogeneity of SOC content of 23,536 samples in a karst watershed, a modified estimation method was determined for SOC storage that exclusively applies to karst areas. The method is a “soil-type method” based on revised calculation indexes for SOC storage. In the present study, the organic carbon contents of different soil types varied greatly, but generally decreased with increasing soil depth. The organic carbon content decreased nearly linearly to a depth of 0–50 cm and then varied at depths of 50–100 cm. Because of the large spatial variability in the karst area, we were able to determine that influences of the different indexes on the estimation of SOC storage decreased as follows: soil thickness > boulder content > rock fragment content > SOC content > bulk density. Using the modified formula, the SOC content in the Houzhai watershed in Puding was estimated to range from 3.53 to 5.44 kg m^?2, with an average value of 1.24 kg m^?2 to a depth of 20 cm, and from 4.44 to 14.50 kg m^?2, with an average value of 12.12 kg m^?2 to a depth of 100 cm. The total SOC content was estimated at 5.39 × 10⁵ t.     

Land use effects on the properties of an Alfisol on the Jos Plateau, Nigeria

This study was carried out to determine the effects of different land-use types on the properties of an Alfisol on the Jos Plateau, Nigeria. Areas being used for nature conservation (forest), grazing and maize cultivation were chosen, and the three are contiguous within a nearly level, moderately well-drained site. Within each of the three land-use areas, a plot of 30 x 20 m was chosen. Each plot was divided into 6 grids of 100 m² size. Within each of these grids, four sampling sites were chosen by throwing up a coin four times. The four surface soil (0–5 cm depth) samples taken at the points where the coin landed, were mixed to form the composite sample, out of which sizeable portion was taken. This means that six soil samples were taken for each land use area (forest, grass, and cultivated). Same procedure was repeated for each of the following soil depths 5–15, 15–30 and 30–50 cm. Laboratory soil analyses were carried out while analysis of variance was used to test the significance of mean difference. The results show that forest clearing for grazing and maize cultivation has lead to significant decreases in most soil fertility variables. Organic matter levels of the grassland and cultivated soils are just about 28% and 13%, respectively, of that of the forest soil in the 0–5 cm depth, while they are 36% and 19%, respectively, in the 5–15 cm depth. Exchangeable cations and effective cation exchange capacity are also significantly higher in the forest soils. The effects are attributable to soil organic matter decomposition and nutrient removal resulting from forest clearance, maize cultivation and grazing. Hence, for sustained agricultural productivity, the soils require adequate inorganic and organic fertilizer additions together with appropriate cultural practices such as agroforestry, crop rotation and mixed cropping involving legumes.     

The effects of hydrometer reading times on the spatial variability of soil textures in southeast Iran

Soil texture is an important physical soil property that may contribute to variations in many soil functions as well as nutrient storage and availability, water retention, and soil erosion. Although several methods for determining the texture classes of soil particles have been proposed, differences among hydrometer reading times have presented challenges in determining the precise soil texture classes. Therefore, this study was conducted to evaluate the effects of hydrometer reading time on the spatial variability of soil textures in the Rafsanjan area, southeast Iran. To accomplish this, 77 soil samples were collected on a 500-m square sampling grid from depths of 0–40, 40–80, and 80–120 cm, and their particle sizes were determined through analysis for 40 s, 2 h, 6.5 h, and 8 h using the Bouyoucos hydrometer method. The results showed a strong spatial correlation in the soil particles among sampling soil layers and across the study area. Moreover, the differences among hydrometer reading times did not have a significant impact on determination of coarse soil texture classes, although they did influence determination of the finer classes. Although the 8 h reading time provided the most accurate response with respect to mechanical analysis of a soil, after 6.5 h the hydrometer could also largely (more than 80.0 %, on average) achieve this goal. Additionally, the 2 h hydrometer reading time could also be useful for the initial assessment or general overview of the soil texture in a certain region; however, it is not recommended for precision agriculture or site-specific management.     

The effect of desertification on carbon and nitrogen status in the northeastern margin of the Qinghai-Tibetan Plateau

Environmental degradation resulting from desertification often accelerates biodiversity loss and alters carbon (C) and nitrogen (N) stocks within grassland ecosystem. In order to evaluate the effect of desertification on plant diversity and carbon (C) and nitrogen (N) stocks, species compositions and C and N contents in plants and soil were investigated along five regions with different degrees of desertification in the northeastern margin of the Qinghai-Tibetan Plateau (control, light, moderate, severe and very severe stages). The study showed: (1) species composition and richness changed significantly with the development of grassland desertification; (2) the aboveground biomass C and N contents in the control were 101.60 and 4.03 g m^?2, respectively. Compared to the control, the aboveground tissue C and N contents significantly decreased from light, moderate, severe to very severe stages. (3) The root C and N contents in the control in 0–40 cm depth are 1,372.83 and 31.49 g m^?2, respectively, while the root C and N contents in 0–40 cm were also declining from the control, light, moderate, severe to very severe stages. (4) Compared to the plant, the soil made a greater contribution for C and N distribution, in which the soil organic C and total N contents in 0–40 cm depth in the control are 20,386.70 and 3,587.89 g m^?2, respectively. At the same time, soil organic C and N contents also decreased significantly from the control to very severe stages. These results suggest that grassland desertification not only alters species compositions and leads to the loss of plant diversity, but also results in greater loss of organic C and N in alpine meadow, in which there is a negative effect on reducing greenhouse gas emission.     

Pasture degradation effects on soil quality indicators at different hillslope positions in a semiarid region of western Iran

A study was made to determine the influence of pasture degradation on soil quality indicators that included physical, chemical, biological and micromorphological attributes, along the hillslope positions in Chaharmahal and Bakhtiari province, western Iran. Soil samples from different slope positions were collected from 0 to 30 cm depth for physical and chemical properties and from 0 to 15 cm depth for biological properties at two adjacent sites in the two ecosystems: natural pasture and cultivated land. Soil quality indicators including bulk density, mean weight diameter, soil organic carbon (SOC), particulate organic material (POM) in aggregate fractions, total nitrogen, available potassium, available phosphorus, cation exchange capacity, soil microbial respiration (SMR) and microbial biomass C and N were determined. The results showed that SOC decreased cultivation from 1.09 to 0.77 % following pasture degradation. The POM decreased by about 19.35 % in cultivated soils when compared to natural pasture; also, SMR and microbial biomass C and N decreased significantly following pasture degradation. Furthermore, aggregate stability and pore spaces decreased, and bulk density increased in the cultivated soils. Overall, our results showed that long-term cultivation following pasture degradation led to a decline in soil quality in all selected slope positions at the site studied in the semiarid region.     

Effects of biochar on aggregate characteristics of upland red soil in subtropical China

Soil aggregation is one of the key properties affecting the productivity of soils and the environmental side effects of agricultural soils. In this study, we aimed to identify whether biochar could be used to improve aggregate stability. A 2-year field experiment was conducted to investigate the effect of biochar application (0, 2.5, 5, 10, 20, 30 and 40 t ha^?1) on aggregate characteristics of upland red soil under a rapeseed–sweet potato rotation in subtropical China. Percentage of aggregate destruction (PAD_0.25), mean weight diameter (MWD), geometric mean diameter (GMD) and fractal characteristics of soil aggregates were measured using both wet and dry sieving methods. Results showed that applying biochar significantly decreased the percentage of aggregate destruction and soil fractal dimension and increased the MWD and GMD. The optimal amelioration was observed when biochar was applied at a rate of 40 t ha^?1. The decline of the fractal dimension of dry aggregates was 2–9 times as much as that of water-stable aggregates in the 0–15 soil layer and 1–4 times in the 15–30 cm soil layer. These results suggested that biochar could improve the resistance of aggregates to stresses and provide scientific strategies for the agricultural production.