Impacts of land‐use intensity on soil organic carbon content,soil structure and water‐holding capacity

The impact of land‐use intensity is evaluated through changes in the soil properties in different areas of the traditional central Spanish landscape. Soil organic carbon (SOC) content, bulk density, aggregate stability and water‐holding capacity (WHC) in the topsoil of active and abandoned vineyards, livestock routes (LR) and young Quercus afforested areas were analysed. These different types of land use can be interpreted as having a gradient of progressively less impact on soil functions or conservation. As soil use intensity declines, there is an increase in SOC content (from 0.2 to 0.6%), WHC (from 0.2 to 0.3 g H₂O per g soil) and aggregate stability (from 4 to 33 drop impacts). Soils beneath vines have lost their upper horizon (15 cm depth) because of centuries‐old tillage management of vineyards. Except for an increase in bulk density (from 1.2 to 1.4 g/cm³), there were no differences in soil characteristics 4 yr after the abandonment of vine management. LR can be considered sustainable uses of land, which preserve or improve soil characteristics, as there were no significant differences between topsoil from LR and that from a 40‐yr‐old Quercus afforested area. SOC content, one of the main indicators for soil conservation, is considered very low in every case analysed, even in the more conservative uses of land. These data can be useful in understanding the slow rate of recovery of soils, even after long‐term cessation of agricultural land use.     

Effects of tractor traffic on spatial variability of soil strength and water content in grass covered and cultivated sloping vineyard

Frequent machinery traffic on sloping vineyard influences spatial distribution of soil physical properties. Our objective was to assess the effects of crawler tractor traffic across the slope (20%) on spatial distribution of soil strength and water content of silt loam soil under controlled grass cover and conventionally cultivated vineyard. The experiment was situated on hillside vineyard (NW, Italy) arranged with rows crosswise the slope. The grass covered treatment included periodical mowing and chopping of herbs and the cultivated treatment—autumn ploughing (18 cm) and spring and summer rotary-hoeing in the vineyard inter-rows (2.7 m). A crawler tractor (2.82 Mg) was used at the same locations across the slope for all tillage and chemical operations. The measurements of soil bulk density, penetration resistance and volumetric water content were done in autumn (after vintage) within the sloping inter-row. The results were analyzed using classic statistics and geostatistics with and without trend. The highest variability was obtained for penetration resistance (CV 56.6%) and the lowest for bulk density (9.6%). In most cases, the semivariograms of the soil parameters were well described by spherical models. The semivariance parameters of all properties measured were influenced by trend. Three-dimensional (3D) maps well identified areas with the highest soil strength in lower crawler ruts being positioned in the upper side of vine row and successively lower strength in upper ruts situated on other side of the same row and inter-rut area. Higher strength in lower than upper ruts was induced by tractor's tilt and resulting higher ground contact pressure. Soil water content in both treatments was the lowest below the upper rut and increased in inter-rut and lower rut areas. The differences in the soil properties between the places within the inter-row were more pronounced in grass covered than in cultivated soil.     

Field-scale study of the variability in pesticide biodegradation with soil depth and its relationship with soil characteristics

The extent of within-field spatial variability of pesticide degradation was characterised in topsoil and subsoil, using the compounds isoproturon, bentazone and mecoprop, which are major contaminants of groundwater and surface freshwater in Europe. Twenty topsoil samples from 0 to 15 cm depth and twenty subsoil samples from 50 to 60 cm depth were collected from a single agricultural field within a 160×90 grid. It was shown that degradation rates of all compounds declined with soil depth. Variability of pesticide degradation rates, pesticide sorption and formation of non-extractable pesticide residues was higher in subsoil relative to topsoil. Furthermore, in the subsoil, there was variation in large scale soil physicochemical composition, which did not occur in topsoil. The greater variability in pesticide degradation rates in subsoil relative to topsoil could be the result of a greater range of degradation kinetics, which could reflect greater spatial variability in the distribution and/or activities of pesticide metabolising communities.     

Spatial pattern and heterogeneity of soil properties in sand dunes under grazing and restoration in Horqin Sandy Land, Northern China

Applying a combination of classical and geostatistical methods, we identified soil properties and their spatial variation in a 5-year grazed sand dune (GSD5) and a 20-year recovered sand dune (RSD20) in Horqin Sandy Land, northern China. The paper assesses the effect of grazing, topography and vegetation restoration on spatial heterogeneity of soil properties. The results showed that soil organic carbon, total nitrogen, very fine sand (0.1–0.05 mm) content and their coefficients of variation were lower in GSD5 than in RSD20, while soil water contents (0–20 cm and 20–40 cm depths) were higher in GSD5 than in RSD20. Geostatistical analysis revealed that the spatial structured variance accounted for the largest proportion of total sample variance in soil properties at the measured scale under grazing and restoration. The spatial autocorrelation ranges were 66.30 m for soil organic carbon and 50.80 m for total nitrogen in GSD5 less than those in RSD20 (70.00 m and 76.10 m, respectively), while the spatial autocorrelation ranges of soil particle size fractions and soil water contents in RSD20 were less than those in GSD5. Kriging-interpolated maps also showed that the heterogeneity of soil organic carbon and total nitrogen and their degree of patch fragmentation were higher in GSD5 than in RSD20. These results suggested that continuous grazing resulted in an increase in spatial variability of soil nutrient and a decrease in spatial variability of soil particle size fractions and soil water content. Soil organic carbon and total nitrogen of sand dunes are associated closely with soil particle size fractions, relative height of sampling site and vegetation cover. Spatial patterns of soil properties are most strongly related to grazing, topography and plant-induced heterogeneity in sand dune ecosystems prone to wind erosion.     

沂蒙山区桃园棕壤斥水性对理化性质的空间响应

以沂蒙山区典型土地利用桃园棕壤为例,在分析降雨前后桃园棕壤斥水性与理化性质空间变异的基础上,探讨了棕壤斥水性对土壤含水量、有机质含量和土壤质地的空间响应特征。按照1 m×1 m网格等间距测定降雨前后土壤实际斥水性与含水量,同时采集表层0~3 cm土壤样品,分析其有机质含量与砂粒、粉粒、黏粒含量,并借助经典统计学、地统计学与空间自相关理论对土壤斥水性及理化性质进行空间格局与空间相关性分析。结果表明:沂蒙山区桃园棕壤的斥水程度强烈,雨后斥水性显著降低;降雨前后棕壤斥水性均具有中等变异水平和较强的空间自相关性,且呈指数模型分布,各向异性显著。受结构变异和随机变异作用,斥水性空间格局沿耕作方向呈条带状分布,在其垂直方向上最小变程为1.4 m。土壤质地是影响棕壤斥水性空间变异的主要因素,斥水性与粉粒含量呈空间正相关,与砂粒和黏粒含量呈空间负相关,相关程度粉粒砂粒黏粒;棕壤斥水性与含水量呈空间负相关,相关度雨前较弱,雨后显著。     

Assessing the variability of soil surface characteristics in row-cropped fields: The case of Mediterranean vineyards in Southern France

Spatial patterns of soil surface characteristics (SSC) are important factors for heterogeneity in runoff and infiltration processes in row-cropped fields. The objective of this paper is to analyse the spatial heterogeneity of SSC in the case of a vineyard in order to propose an adequate sampling strategy. A preliminary field survey was carried out to obtain a quantitative assessment of SSC. The experimental layout consisted of 3 wire-trained vine subplots with 3 different soil treatment. 60 observations per subplot were conducted using the line transect method. Their locations were determined according to a stratified sampling design conceived in accordance with the geometric structure of the vineyard system, defined by the alignment of vine rows and the direction of the main slope. The spatial heterogeneity of SSC was analysed at intra-transect and inter-transect levels using measurements of structural crust, sedimentary crust, grass and organic litter. The characterization of intra-transect heterogeneity, using join-count statistics, allowed patches of homogeneous units of attributes to be detected and hence an appropriate sampling resolution and an adequate transect length to be determined. A sampling resolution of 10 cm on a 1.25 m length transect was found to be appropriate for the observation of homogeneous units of attributes. Analysis of inter-transect heterogeneity, using non-spatial statistics, revealed considerable variability between rows and inter-rows that must be accounted for during field surveys. The role of site topography on spatial patterning of SSC attributes across the plot and the need to stratify the plot into areas with homogeneous slope were also demonstrated. Finally, the t-test procedure indicated that the minimum sample size was found to be 200 transect/ha for a minimum precision rate of 80% in the values of SSC attributes.     

Cropping systems and bed width effects on runoff,erosion and soil properties in a rainfed Vertisol

The effects of two bed widths (1 and 2 m) and four rainfed cotton‐based cropping systems on soil properties, runoff and erosion were evaluated in a Vertisol (1 per cent slope; 21 g per 100 g sand, 12 g per 100 g silt, 67 g per 100 g clay) in subtropical central Queensland, Australia. The cropping systems were: early cotton (Gossypium hirsutum L.) sown between August and October; wheat (Triticum aestivum L.) sown in May, sprayed out and followed by early cotton; wheat allowed to mature, harvested and followed by late cotton sown between October and December; and grain sorghum (Sorghum bicolor (L.) Moench.) followed by cotton. Land preparation was by minimum tillage and traffic was restricted to the furrows between the beds. Rainfall runoff and soil erosion were monitored with water‐height recorders, flumes and troughs. Soil structure was evaluated as air‐filled porosity of oven‐dried soil in the 0–0.15, 0.15–0.30, 0.30–0.45 and 0.45–0.60 m depths. Soil chemical properties measured in the 0–0.15 m depth were organic carbon, pH (in 0.01 M CaCl₂), electrical conductivity (EC_1:5) of a 1 : 5 soil : water suspension and exchangeable Ca, Mg, K and Na. In comparison with 1 m beds, 2 m beds resulted in lower runoff and soil erosion, lower exchangeable Na, exchangeable sodium percentage and higher EC_1:5/exchangeable Na, higher rate of soil organic matter decrease and better soil structure in the 0–0.15 m depth. Runoff and erosion were reduced, and cotton lint yields increased either by cropping systems sown early to intercept most of the seasonal rainfall or by those which produced a high level of ground cover. Soil physical and chemical properties were best, and runoff and erosion lowest with 2 m beds and cropping systems producing a high level of ground cover. Copyright © 2002 John Wiley & Sons, Ltd.     

应用土壤质地预测干旱区葡萄园土壤饱和导水率空间分布

田间表层土壤饱和导水率的空间变异性是影响灌溉水分入渗和土壤水分再分布的主要因素之一,研究土壤饱和导水率的空间变化规律,有助于定量估计土壤水分的空间分布和设计农田的精准灌溉管理制度。为了探究应用其他土壤性质如质地、容重、有机质预测土壤饱和导水率空间分布的可行性,试验在7.6 hm2的葡萄园内,采用均匀网格25 m×25 m与随机取样相结合的方式,测定了表层(0～10 cm)土壤饱和导水率、粘粒、粉粒、砂粒、容重和有机质含量,借助经典统计学和地统计学,分析了表层土壤饱和导水率的空间分布规律、与土壤属性的空间相关性,并对普通克里格法、回归法和回归克里格法预测土壤饱和导水率空间分布的结果进行了对比。结果表明:1)土壤饱和导水率具有较强的变异性,平均值为1.64 cm/d,变异系数为1.17;2)表层土壤饱和导水率60%的空间变化是由随机性或小于取样尺度的空间变异造成;3)土壤饱和导水率与粘粒、粉粒、砂粒和有机质含量具有一定空间相关性,而与土壤容重几乎没有空间相关性;4)在中值区以土壤属性辅助的回归克里格法对土壤饱和导水率的预测精度较好,在低值和高值区其与普通克里格法表现类似。研究结果将为更好地描述土壤饱和导水率空间变异结构及更准确地预测其空间分布提供参考。     

Spatial variability of Southeastern U.S. Coastal Plain soil physical properties: Implications for site-specific management

Our objectives were to describe the field-scale horizontal and vertical spatial variability of soil physical properties and their relations to soil map units in typical southeastern USA coastal plain soils, and to identify the soil properties, or clusters of properties, that defined most of the variability within the field. The study was conducted on a 12-ha field in Kinston, NC. A 1:2400 scale soil survey had delineated three soil map units in the field: Norfolk loamy sand, Goldsboro loamy sand, and Lynchburg sandy loam. These are representative of millions of hectares of farmland in the Coastal Plain of the southeastern USA. Sixty soil cores were taken to ∼ 1-m depth, sectioned into five depth increments, and analyzed for: soil texture as percentage sand, silt, and clay; soil water content (SWC) at − 33 and − 1500 kPa; plant available water (PAW); saturated hydraulic conductivity (Ksat); bulk density (BD); and total porosity. A penetrometer was used to measure cone index (CI) at each sample location. Variography, two mixed-model analyses, and principal components analysis were conducted. Results indicated that soil physical properties could be divided into two categories. The first category described the majority of the within-field variability and included particle size distribution (soil texture), SWC, PAW, and CI. These characteristics showed horizontal spatial structure that was captured by soil map units and especially by the division between sandy loams and finer loam soils. The second class of variables included BD, total porosity, and Ksat. These properties were not spatially correlated in the field and were unrelated to soil map unit. These findings support the hypothesis that coastal plain soil map units that delineate boundaries between sandy loams versus finer loam soils may be useful for developing management zones for site-specific crop management.     

Spatial variability of soil organic carbon stock in an olive orchard at catchment scale in Southern Spain

Orchards have a high potential for carbon sequestration. However, little research is available on the spatial variability at catchment scale and on the difference between the tree area and the lanes. We analyzed theik spatial variability of soil organic carbon stock, SOC_stock at 90 cm depth in an 8-ha catchment in Southern Spain with olives on a vertic soil. Results showed higher soil organic carbon concentration, SOC, in the tree area as compared to the lane up to 60 cm depth, but its impact on SOC_stock was negligible since it was compensated by the higher soil bulk density in the lane. SOC at different depths was correlated with that in the top 0–5 cm. The overall SOC_stock of the orchard was 4.14 kg m⁻², ranging between 1.8 and 6.0 kg m⁻². This SOC_stock is in the mid-lower range of values reported for olive orchards, measured at smaller scale, and similar to those other intensive field crops and agroforestry under comparable rainfall conditions. The spatial variability in SOC_stock was correlated to several geomorphological variables: elevation, cumulative upstream area, topographic wetness index, sediment transport index, and tillage erosion. Differences in SOC and SOC_stock are driven by the sediment redistribution downslope, mainly by tillage erosion, and higher soil water availability in lower areas allowing higher biomass production. These topographic indexes and the correlation between SOC in the topsoil and SOC_stock up to 90 cm should be further explored in other typology of olive orchards for facilitating the mapping of SOC_stock.     

Enhancing pedotransfer functions with environmental data for estimating bulk density and effective cation exchange capacity in a data‐sparse situation

Soil bulk density (BD) and effective cation exchange capacity (ECEC) are among the most important soil properties required for crop growth and environmental management. This study aimed to explore the combination of soil and environmental data in developing pedotransfer functions (PTFs) for BD and ECEC. Multiple linear regression (MLR) and random forest model (RFM) were employed in developing PTFs using three different data sets: soil data (PTF‐1), environmental data (PTF‐2) and the combination of soil and environmental data (PTF‐3). In developing the PTFs, three depth increments were also considered: all depth, topsoil (<0.40 m) and subsoil (>0.40 m). Results showed that PTF‐3 (R²; 0.29–0.69) outperformed both PTF‐1 (R²; 0.11–0.18) and PTF‐2 (R²; 0.22–0.59) in BD estimation. However, for ECEC estimation, PTF‐3 (R²; 0.61–0.86) performed comparably as PTF‐1 (R²; 0.58–0.76) with both PTFs out‐performing PTF‐2 (R²; 0.30–0.71). Also, grouping of data into different soil depth increments improves the estimation of BD with PTFs (especially PTF‐2 and PTF‐3) performing better at subsoils than topsoils. Generally, the most important predictors of BD are sand, silt, elevation, rainfall, temperature for estimation at topsoil while EVI, elevation, temperature and clay are the most important BD predictors in the subsoil. Also, clay, sand, pH, rainfall and SOC are the most important predictors of ECEC in the topsoil while pH, sand, clay, temperature and rainfall are the most important predictors of ECEC in the subsoil. Findings are important for overcoming the challenges of building national soil databases for large‐scale modelling in most data‐sparse countries, especially in the sub‐Saharan Africa (SSA).     

Spatial distribution of soil salinity and potential implications for soil management in the Manas River watershed,China

Understanding the watershed-scale spatial distribution of soil salinity and its compositions is important for soil management. Here, we present the first study on the Manas River watershed in northwest China. In this study, we took soil samples in upper 20 cm of soil from 186 locations across the watershed and measured total salt concentration (TSC), salt ion composition and soil particle size distribution (PSD). We found that on average topsoil TSC tended to increase, from 3.55 g kg⁻¹ in upstream regions to 19.40 g kg⁻¹ in downstream regions. The stoichiometric analysis showed that the equivalence ratio of soil Cl^- to SO₄²⁻ increased from 0.53 in upstream regions to 2.12 in midstream regions, and further to 3.76 in downstream regions; thus, the soil types were classified into chloride–sulfate, sulfate–chloride and chloride soils types, respectively. Additionally, proportions of small (<2 μm in diameter) and large (>2,000 μm) soil particles increased, while that of medium sizes (2–50 μm) decreased from upstream to downstream, with an increasing coefficient of variance (CV) in PSD. Taken together, watershed-scale topsoil salinity may be horizontally characterized by increased TSC and Na⁺ & Cl⁻ proportions, greater equivalence ratio of Cl⁻ vs. SO₄²⁻ and more balanced distribution of PSD along with surface water flow. Results demonstrated that soil salinity and its ions compositions showed a great variation across the watershed scale, suggesting that soil management may consider the spatial heterogeneity of saline–alkaline soil types, and our results provided scientific guidance for local soil management and restoration.     

Peak functions for modeling high resolution soil profile data

Parametric and non-parametric depth functions have been used to estimate continuous soil profile properties. However, some soil properties, such as those seen in weathered loess, have anisotropic peak-shaped depth distributions. These distributions are poorly handled by common parametric functions. And while nonparametric functions can handle this data they lack meaningful parameters to describe physical phenomena in the depth distribution of a property such as a peak, an inflection point, or a gradient. The objective of this work is to introduce the use of asymmetric peak functions to model complex and anisotropic soil property depth profiles. These functions have the advantages of providing parameters, which quantify or describe pedogenic processes. We demonstrate the application of the Pearson Type IV (PIV) and the logistic power peak (LPP) functions to high resolution soil property depth profiles measured by diffuse reflectance spectroscopy in a claypan soil landscape of Northeastern Missouri, USA. Both peak functions successfully fit clay, silt, and pH data for an example soil profile from a summit landscape position (R² = 0.90 for pH and 0.98 for silt and clay). The LPP function was further demonstrated to fit clay depth distribution for a shoulder, backslope, footslope, and a depositional landscape position (R² = 0.98, 0.96, 0.96, 0.91). Relationships between the fitted parameters of these profiles were useful to describe landscape trends in their morphological features and show promise to continuously describe pedogenic processes in three dimensions. Peak functions are a useful companion to high-resolution soil profile data collected by sensors and their combined use may allow more intensive mapping and better explanation of soil landscape variability.     

Erfassung der Variabilität von Bodenmerkmalen in einem Blindversuch auf Fahlerde mittels Methoden der räumlichen Statistik

Variability of soil parameters in a uniformity trial on a Luvisol evaluated by means of spatial statistics The relationships between soil parameters and indicators of soil genesis were investigated in a uniformity trial on Luvisol by means of classical and spatial statistics. The following properties were investigated in the topsoil (0–30 cm) and subsoil (31–40 cm): content of total carbon (C_t), content of clay plus fine silt (FAT), concentrations of available potassium (K) and phosphorus (P), and pH values. The depth loamy Bt horizon and microrelief were considered as indicators of soil genesis. Smoothing of the raw data by means of block kriging eliminated the small scale variability of all parameters. In this way, the rank correlation coefficients between soil parameters increased by factor 2 and were to 0.52 for C_t–FAT; 0.69 for C_t–K, and 0.55 for C_t–P in the top soil. The maps for smoothed data allowed a much better visual analysis of spatial distribution of investigated properties compared to the raw data. The significant correlations as well as the similarity of maps and variograms suggested that the spatial variability of FAT, C_t, K, and P in the top soil was determined by the same factors. The depth of the loamy Bt horizon and the relief were the most important factors defining the distribution of the investigated soil parameters. The rank correlation coefficients of the smoothed and detrended relief with the soil parameters amount to –0.63, –0.77, –0.71, and –0.57 for FAT, C_t, K, and P, respectively.     

Spatial variability of topsoils and vegetation in a grazed steppe ecosystem in Inner Mongolia (PR China)

It is not clear from the literature how the spatial distribution of topsoil and vegetation properties is affected by grazing cessation. Thus, the objective of this study was to elucidate if long‐term grazing exclosure increases spatial heterogeneity of topsoil and vegetation properties in a steppe ecosystem in NE China. Variograms and crossvariograms were calculated for bulk density, organic carbon (OC), total N, and total S concentration, δ¹³C, pH, Ah horizon thickness, vegetation cover, and aboveground biomass. Five sites with different grazing intensities (ungrazed since 1979, ungrazed since 1999, winter grazing, continuously grazed, heavily grazed) were sampled with two different grid sizes, allowing the exploration of scale effects. Small grids (15 m spacing, 5 m nested sampling) exhibited a different spatial structure compared to large grids (50 m spacing, 10 m nested sampling). Spatial distribution in small grids changed with grazing intensity. Generally, heterogeneity of topsoil properties increased with decreasing grazing intensity from a homogeneous to a patchy distribution. We attribute this to vegetation recovery/succession and deposition of windblown material in ungrazed areas. The plot ungrazed since 1999 showed different spatial dependencies than continuously and heavily grazed plots, but has not yet reached the high variability of the plot which was ungrazed since 1979. Large grid sampling did not detect small‐scale variability or grazing impacts, but showed spatial dependencies that were attributed to topography or soil erosion/deposition. Low OC concentration and low Ah thickness were associated with hilltop and shoulder positions, resulting in lower OC stocks at these topographic units.     

Spatial variability of soil water content and mechanical resistance of Brazilian ferralsol

The spatial variability of mechanical resistance to penetration (PR) and gravimetric moisture (GM) was studied at a depth of 0–0.40 m, in a ferralsol cropped with corn, and under conventional tillage in Ilha Solteira, Brazil (latitude 20°17′S, and longitude 52°25′W). The purpose of this study was to analyse and to try explaining the spatial variability of the mentioned soil physical properties using geostatistics. Soil data was collected at points arranged on the nodes of a mesh with 97 points. Geostatistics was used to analyse the spatial variability of PR and GM at four depths: 0–0.1, 0.1–0.2, 0.2–0.3 and 0.3–0.4 m. PR showed a higher variability of data, with coefficients of variation of 52.39, 30.54, 16.91, and 15.18%, from the surface layers to the deepest layers. The values of the coefficients of variation for GM were lower: 9.99, 5.13, 5.59, and 5.69%. Correlation between GM and PR for the same soil layers was low. Penetration resistance showed spatial structure only in the 0.30–0.40 m layer, while gravimetric moisture showed spatial structure at all depths except for 0–0.10 m. All the models of fitted semivariograms were spherical and exponential, with ranges of 10–80 m. Data for the variable ‘GM’ in the 0.20–0.30 and 0.30–0.40 m layers revealed a trend in data attributed to the occurrence of subsurface water flow.     

Scale- and location-dependent correlations of soil strength and the yield of wheat

The relationship between soil strength and crop yield may be summarized by a linear correlation coefficient (usually negative). It is likely, however, that this over-simplifies a complex situation in which the relationship between these variables depends on spatial scale and location. We used the wavelet transform to assess this scale- and location-dependence. We established a transect on an arable field in Eastern England, and studied the correlations of soil strength (top- and subsoil) with crop yield. The transect comprised 267 contiguous 0.72 m × 0.72 m plots. Measurements were taken during two consecutive growing seasons of winter wheat (harvest dates of August 2004 and 2005). Soil strength was measured with a penetrometer in the spring of each growing season. As expected, the overall correlation of soil strength with yield was negative but weak. Wavelet analysis revealed that, at fine spatial scales, topsoil and subsoil strength were correlated more or less equally with yield; however, at coarse spatial scales, topsoil strength had a stronger correlation with yield than did subsoil strength. The correlation of topsoil strength with yield at fine spatial scales (corresponding to about 1 m on the ground) was negative. A likely source of this fine-scale variation was the soil compaction associated with tractor wheelings. The correlation of topsoil strength with yield at the coarsest spatial scale (corresponding to about 50 m on the ground) was positive. This correlation was temporally stable, and might have reflected how soil strength can act as a proxy for other soil attributes. In the 2005 growing season, we found evidence that, at intermediate spatial scales, the correlation of soil strength with yield changed depending on the position on the transect. This was probably due to an interaction between the compaction associated with tractor wheelings and the local soil conditions. There was no evidence of such location-dependence in the correlation of soil strength with yield in the 2004 growing season. In summary, the effect of soil strength on crop yield was not expressed in a constant negative correlation across all spatial scales and locations: the negative correlation occurred mainly at fine spatial scales, and the correlation changed according to the position in the landscape and the prevailing local soil conditions.     

Organic carbon in soil physical fractions under different-aged plantations of Mongolian pine in semi-arid region of Northeast China

In order to understand the changes of surface soil carbon (C) storage following the afforestation of sandy grasslands, we used physical fractionation procedures to quantify C concentrations and sucrase enzyme activity in bulk soil and different particle fractions along two replicate chronosequences of Mongolian pine (Pinus sylvestris var. mongolica Litv.) plantations in the southeastern Keerqin Sand Lands, Northeast China. Carbon concentration in bulk topsoil (0–15 cm) initially decreased following afforestation of grassland and subsequently increased as the forest matured. In general, this pattern of C concentration changes was associated with all particle-size fractions (except clays) and both macro- and microaggregates. The patterns of topsoil C were also influenced by wind erosion and deposition, with marked increases in the relative mass of silt and fine sand fractions occurring during forest development. The loss of aggregates immediately following afforestation was counteracted by formation of aggregates as the forests developed, contributing to the stabilization of carbon. To enhance soil C storage during afforestation of sandy soils in such semi-arid regions it is recommended to minimize disruption of grassland vegetation during the planting stage.     

Short‐scale distribution of copper fractions in a vineyard acid soil

We studied short‐scale variation in the total concentration of copper and its fractions in a soil vineyard. Soil samples were collected at a depth of 0–20 cm between plant rows (1), between individual plants (2) and at their base (3) in a vine‐grown plot in NW Spain. The mean total content in Cu (Cu_t) in the soil was found to be 97 mg kg⁻¹ and that of potentially available Cu (Cu_EDTA) 34 mg kg⁻¹. Copper bound to organic matter (Cu_OM) and to non‐crystalline inorganic soil components (Cu_IA) were the dominant fractions and accounted for 34% of total copper each. The contents in exchangeable (Cu_e), pyrophosphate‐extractable (Cu_p), oxalic/oxalate‐extractable (Cu_o) and total copper (Cu_t) exhibited statistically significant correlations with pH, sum of base cations (S), cation‐exchange capacity (CEC) and exchangeable calcium (Ca_e). Both total and fractional copper contents were higher in plant rows than between them, particularly in the centre of the plot. Also, Cu_OM and Cu_IA were higher in planting rows than between rows. These copper results may have been influenced by the vine‐growing practices of the area and also by the distribution of plants and their pruning. This variability pattern for Cu distribution is crucial with a view to minimising potential adverse effects of fungicides and optimising any reclamation treatments needed. Copyright © 2007 John Wiley & Sons, Ltd.     

Spatial variability of selected soil properties and its impact on the grain yield of oats (Avena sativa L.) in small fields

Abstract

To investigate spatial variability in topsoil (0–20?cm) pH, available phosphorus (P), potassium (K), total nitrogen (N), and soil organic matter (SOM) of small fields (～2?ha), and to determine the impact of soil heterogeneity on the spatial variability of crop yield two fields were cropped with spring oats and one with winter wheat under humid-temperate conditions. In the two oat fields, some of the measured soil properties (P, K) and the grain yield varied considerably, and strong spatial trends were recorded for most of the soil traits. In the third field, soil properties showed only a moderate spatial variation, and no spatial trends were found. The spatial distribution of SOM and total N in the topsoil had some influence on the spatial pattern of the oat grain yield in the field of Gränichen; however, spatial relationships between soil chemical properties and grain yield were rather weak in our study.