Selected Soil Attributes Research Articles

Could Airborne Geophysical Data Be Used to Improve Predictive Modeling of Agronomic Soil Properties in Tropical Hillslope Area?

Airborne geophysical data (AGD) have great potential to represent soil-forming factors. Because of that, the objective of this study was to evaluate the importance of AGD in predicting soil attributes such as aluminum saturation (ASat), base saturation (BS), cation exchange capacity (CEC), clay, and organic carbon (OC). The AGD predictor variables include total count (μR/h), K (potassium), eU (uranium equivalent), and eTh (thorium equivalent), ratios between these elements (eTh/K, eU/K, and eU/eTh), factor F or F-parameter, anomalous potassium (Kd), anomalous uranium (Ud), anomalous magnetic field (AMF), vertical derivative (GZ), horizontal derivatives (GX and GY), and mafic index (MI). The approach was based on applying predictive modeling techniques using (1) digital elevation model (DEM) covariates and Sentinel-2 images with AGD; and (2) DEM covariates and Sentinel-2 images without the AGD. The study was conducted in Bom Jardim, a county in Rio de Janeiro-Brazil with an area of 382,430 km², with a database of 208 soil samples to a predefined depth (0–30 cm). Non-explanatory covariates for the selected soil attributes were excluded. Through the selected covariables, the random forest (RF) and support vector machine (SVM) models were applied with separate samples for training (75%) and validation (25%). The model’s performance was evaluated through the R-squared (R2), root mean square error (RMSE), and mean absolute error (MAE), as well as null model values and coefficient of variation (CV%). The RF algorithm showed better performance with AGD (R2 values ranging from 0.15 to 0.23), as well as the SVM model (R2 values ranging from 0.08 to 0.23) when compared to RF (R2 values ranging from 0.10 to 0.20) and SVM (R2 values ranging from 0.04 to 0.10) models without AGD. Overall, the results suggest that AGD can be helpful for soil mapping. Nevertheless, it is crucial to acknowledge that the accuracy of AGD in predicting soil properties could vary depending on various common factors in DSM, such as the quality and resolution of the covariates and available soil data. Further research is needed to determine the optimal approach for using AGD in soil mapping.

Impact of Soil and Water Conservation Measures and Slope Position on Selected Soil Attributes at a Watershed Scale

The Ethiopian highlands are affected by soil erosion resulting in the deterioration of soil properties. To reverse this, different soil and water conservation (SWC) measures were spatially practiced; however, the effect of SWC and slope gradient on soil properties is not well studied in the area. Hence, this study was conducted to evaluate the effects of SWC and slope gradient on selected soil physicochemical properties in Dawnt watershed, northwestern Ethiopia. The treatments were a combination of four different SWC measures on three slope gradients replicated at three sites. Disturbed and undisturbed soil samples were collected from 0–20 cm soil depth, and physicochemical properties were determined following standard laboratory procedures. The laboratory results depict that sand, bulk density, moisture, particle density, porosity, pH, organic carbon (OC), cation exchange capacity (CEC), total nitrogen, and available phosphorus were significantly ( P < 0.05 ) affected by SWC measures and slope gradient. High OC (2.44%), CEC (45 cmol (+) kg−1), and moisture (19.55%) were obtained from stone-faced soil bund stabilized with grass (SFSBG) and higher available phosphorus (7.83 ppm) from soil bund (SB), while lower bulk density (1.13 gm/cm3) was obtained from SFSBG. Additionally, higher clay (41.67%) and moisture (19.81%), and lower bulk density (1.14 g·cm−3) were obtained from the lower slope. Higher pH (6.75) and OC (2.89%) were recorded at the lower slope under SFSBG and lower pH and OC (6.03 and 1.02%) at the upper slope with nonconserved. Soil chemical properties, except available potassium, were increased down the slope. The interactions of slope position and SWC measures affect soil texture, pH, organic carbon, and available phosphorus but not affect soil bulk density, moisture content, particle density, total porosity, cation exchange capacity, total nitrogen, and available potassium. In general, the soil properties were improved through integrating conservation practices with multipurpose grass species across the study watershed. Therefore, it is possible to infer that SFSBG measures improve the observed physicochemical soil properties, which urge for the maintenance and the development of SWC measures in the study watershed as well as nearby highlands with similar topographic conditions and agroclimatic characteristics.

Variability and correlation of selected soil attributes and maize yield influenced by tillage systems in mountainous agroecosystem

Soil and topographic variability severely influence agricultural productivity and food security in a mountainous agroecosystem. Understanding these soil spatial disparities are important to optimize suitable land use planning and adoption of appropriate conservation practices to ensure sustainable agricultural productivity in mountainous regions. A field survey and sampling of 108 elevation sites were conducted to assess spatial dynamics and influence of prevalent tillage systems on selected soil attributes and on reported maize (<i>Zea mays</i> L.) grain yield (MGY) in mountainous valleys of Pakistan. Measured soil properties were effective soil depth (ESD), soil penetration resistance (SPR), soil bulk density (SBD), fraction of rock fragments (FRF), soil organic matter (SOM), and soil water holding capacity (SWHC). Additionally, the influence of three existing tillage systems—integrated tillage (IT), bullock tillage (BT), and tractor tillage (TT)—on soil properties and MGY were assessed. Research results showed that ESD, SPR, SBD, FRF, SOM, SWHC, and MGY varied from 15.0 to 40.0 cm, 180.0 to 278.0 psi, 0.9 to 1.7 g cm⁻³, 13.2% to 43.5%, 0.6% to 2.9%, 10.5% to 35.6%, and 4.1 to 10.2 t ha⁻¹, respectively. Differences between soil parameters were significant among the sampling sites studied. Soil properties were found to be strongly associated with each other and with the MGY and were grouped through Pearson correlation, principal component analysis, and heatmap. Moreover, significant variation of soil properties was noted due to the tillage systems adopted by the farmers. The ESD (26.8 cm), SOM (1.4%), SWHC (16.9%), and MGY (7.8 t ha⁻¹) were the highest under IT while the SPR (262.8 psi), SBD (1.6 g cm⁻³), and FRF (38.0%) were the greatest with TT compared to the other tillage systems. Findings of this study are imperative for agriculturists, soil managers, land use planners, and policy makers to identify and implement suitable interventions for sustainable use of agricultural lands to bring economic produce while conserving the mountainous agroecosystem and its resources on sustainable basis.

Ecological network analysis to assess the restoration success of disturbed mine soil in Zoucheng, China

AbstractUnderstanding the interactions among soil microbial species and how they respond to land reclamation is essential to evaluate the success of ecological restoration actions in disturbed mine soil. In this study, we strived to reveal the interactions among soil bacterial communities along the reclamation timeline of a coal mine in Zoucheng, China. To do so, we investigated changes in the composition of soil bacterial over time and constructed molecular ecological networks (i.e., microbial network) following mining soil reclamation into agricultural land. The relationships between microbial networks and selected soil attributes (i.e., soil pH, electric conductivity, organic matter, soil nutrients and enzymatic activities) were also analyzed. The results showed that the composition of soil bacteria changed significantly along the reclamation timeline. The microbial network profile revealed that Acidobacteria, Planctomycetes and Proteobacteria were the key microbial populations. Soil pH, soil organic matter content, soil dehydrogenase and urease activities were significantly correlated (0.001 ≤ p &lt; 0.05) with the microbial network structure, suggesting that the microbial networks found influenced the provision of relevant soil ecological functions after reclamation. The variation in complexity of the microbial networks along the reclamation timeline revealed that microbial development was promoted by the shift in land use from mining into agriculture. Overall, our findings shed light on how soil microbial communities and networks change following mine reclamation into agricultural land. The results presented herein will undoubtedly aid in the establishment of success indicators of ecological restoration activities in disturbed mining soil.

Sustainability Assessment of Smallholder Farms in the Savannah Transition Agro-Ecological Zone of Ghana

The ever-increasing human population has resulted in political pressure to increase crop production. Currently, smallholder farmers are expected to be environmentally considerate, adapt to extreme climatic conditions and deal with financial instability. Despite these recent developments, farmers and their farming activities in these rural environs of developing countries need to improve household food and income security on a sustainable basis. A minimum data set selected from extensive data was used to determine indicators for soil sustainability assessment. This method involved expert opinion and statistical data reduction techniques. The results indicated that SOC, MBC, BS, EC, Spo and sand were the most important variables selected as MDS using PC analysis. Forest and Grassland had a high sustainability index (SI) while Savannah woodland, Fallow and Cropland were rated not sustainable (NS). For Cumulative rating using the total dataset (CR-TDS), Forest had a high sustainability index (HS), Savannah woodland and Grassland were sustainable (S) compared to Fallow and Cropland, which were sustainable with high input (SWHI). Also, for cumulative rating using the minimum dataset (CR-MDS), Forest, Savannah woodland and Grassland had high sustainability (SH) indices compared to Fallow and Cropland, which were considered sustainable with high input (SWHI). Sustainability index (SI) and Cumulative rating (CR) using the total dataset (CR-TDS) had a strong correlation (R2 = 0.91, p 2 = 0.44, p 2 = 0.60, p < 0.05). These methods consider that these management goals dictate soil functions affecting the selection of indicators. Using PCA and variance analysis, silt, clay, EC, SOC, MBC and CEC relating to soil texture and fertility were identified as the most influential (sensitive) indicators for soil sustainability assessment. The selected soil attributes can serve as target indicators for soil fertility restoration, erosion control and management in the Nkoranza district. Therefore, a farm-level sustainability index for small-scale and commercial farms is proposed based on readily available data for the Savannah Transition Agro-ecozone of Ghana.

Applied gamma-ray spectrometry for evaluating tropical soil processes and attributes

Geophysical methods, such as gamma-ray spectrometry, have great potential to enhance knowledge of the pedosphere (pedogenesis, pedogeochemistry and pedogeomorphology), helping to predict tropical soil attributes. We applied proximal gamma-ray spectrometry to evaluate tropical landscape dynamics, pedogenesis and spatial distribution of radionuclides and selected soil attributes. This study was carried out in southeast Brazil, where 79 soil samples (0–20 cm) along transects were collected to perform physical-chemical analysis coupled with collection of surface gamma-ray spectrometric data, allowing the detection of the radionuclides uranium (U238), thorium (Th232), and potassium (K40). Additionally, we analyzed soils in four toposequences, with varying lithology, relief, and hydrology. The radionuclide concentrations in soils showed a direct relationship with the parent material composition, either rocks or sediments. Weathering degree and the geochemical behavior of each radionuclide determines its permanence or removal in soils. Denudation processes along the toposequences also influence the distribution of radionuclides. On one hand, the radionuclide contents of mature, weathered soils are closely associated with advanced pedogenesis, with a higher clay contents and argic horizon formation, whereas in younger, less weathered soils the parent material exerts a greater influence than pedogenesis. Uranium decreased with altitude, and showed greater mobility compared with thorium. Thorium presented a higher correlation with clay content, and the opposite with sand content. Potassium detection increased with soil cation exchange capacity (CEC) and clay content. Gamma-spectrometry detected significant variations in some segments along the toposequences, undetectable by conventional soil survey techniques. This may indicate changes from one soil class to another or the continuity of a particular soil class, demonstrating the potential of this tool in digital soil mapping, pedogeochemical, pedogeomorphological and pedogenesis processes studies.

Characterizing selected soil attributes of different land-use management to assess reforestation benefits of deforested riparian buffers

IntroductionThe information available on the sensitivity of soil biotic and abiotic attributes, which can be used to track the impact of reforestation in riparian buffers, is often insufficient to refine management practices and convince stakeholders of the benefits of reforestation.MethodsIn this study, conducted in Victoria, Australia, the changes in soil biotic and abiotic attributes, organic carbon (OC), mineral nitrogen (MN), total dissolved solutes (TDS) and pH were characterised to assess the impact of land-use change from bare riparian (BR) to reforested riparian (RR). Additionally, the benefits of revegetating a deforested creek bank with regard to salinity abatement and C-sequestration potentials were assessed.ResultsThe TDS depletion in the RR strips varied spatiotemporally from 65 to 169 mg/L, the net OC deposition from 16 to 19 g C/kg soil and MN deposition from 1.2 to 2.1 g N/kg soil, respectively. Additionally, the net changes in pH from alkaline to near neutral condition varied by 0.4 to 1.0 pH units. Approximately 30% to 60% of the net OC depletion after deforestation was redeposited under RR over 3 to 6 years. The TDS depletion after land-use changed from BR to RR ranged from 15 to 32% over 3 to 6 years.ConclusionThe soil attributes OC, MN and TDS characteristics under different land-use practices varied spatiotemporally. This information may be useful to convince stakeholders to undertake reforestation of creek banks for salinity abatement, and that change in land-use has the potential to increase C sequestration at a farm scale.

Spatial Variability of Selected Soil Attributes under Agricultural Land Use System in a Mountainous Watershed, Ethiopia

In the Ethiopian Highlands, research projects were often measuring soil attributes of spatially structured point data but soil variability at a watershed scale is not clearly defined. This study was conducted to assess the correlation among selected soil attributes and to illustrate the spatial pattern and dependence of neighboring observations. The 53.7 km2 study watershed was divided into a 500 m by 500 m square grid using arcgis and at the center of each grid soil samples from 0 to 25 cm depth were collected within 184 locations. The descriptive statistics revealed available phosphorous (AP) had the largest coefficient of variation (CV = 104) while pH was the least variable. There was a positive link between elevation and SOC whereas bulk density (ρd) and pH indicated an inverse relationship with elevation and SOC. The value for nugget/sill of ρd, pH and elevation are less than 0.25, and depicts that it has strong spatial autocorrelation. The value for nugget/ sill of SOC, and TN found between 0.25 and 0.75, and indicate that they have moderate spatial autocorrelation. With regard to AP, the value for nugget/sill is more than 0.75, which displays a weak spatial autocorrelation. Semivariograms of ρd, pH and elevation were best fitted to Gaussian model whereas SOC, TN and AP were best fitted to exponential function. Generally, the study verified that soil measurements taken at the given scale through regular sampling interval were adequate to capture the spatial dependence of numerous initial soil assessments in the study watershed.

Spatial Variability of Selected Soil Properties in Relation to Different Land Uses in Northern Kgalagadi (Matsheng), Botswana

Spatial variability of selected soil attributes were investigated in the Kgalagadi region. Soil samples were collected along transects at Hukuntsi, Tshane, Lokgwabe and Lehututu at 50 m, 200 m, 500 m, 1000 m, 2000 m and 5000 m from water sources located in areas of different land use types. Sampling depth was 0 - 10 cm, 50 - 70 cm and 100 - 120 cm. Samples were analysed for pH, EC, SOC, and P. Soil pH and EC were relatively high around CGA Pans, while SOC and P were generally low in the whole study area. It was concluded that the assumptions that different land use types existed under various soil environments with different soil properties, and that different land use types influence soil characteristics in various ways in the study area were not true.

Emissions of nitrous oxide from arable organic and conventional cropping systems on two soil types

Conventional cropping systems rely on targeted short-term fertility management, whereas organic systems depend, in part, on long-term increase in soil fertility as determined by crop rotation and management. Such differences influence soil nitrogen (N) cycling and availability through the year. The main objective of this study was to compare nitrous oxide (N 2O) emissions from soil under winter wheat ( Triticum aestivum L.) within three organic and one conventional cropping system that differed in type of fertilizer, presence of catch crops and proportion of N 2-fixing crops. The study was replicated in two identical long-term crop rotation experiments on sandy loam soils under different climatic conditions in Denmark (Flakkebjerg—eastern Denmark and Foulum—western Denmark). The conventional rotation received 165–170 kg N ha −1 in the form of NH 4NO 3, while the organic rotations received 100–110 kg N ha −1 as pig slurry. For at least 11 months, as from September 2007, static chambers were used to measure N 2O emissions at least twice every calendar month. Mean daily N 2O emissions across the year ranged from 172 to 438 μg N m −2 d −1 at Flakkebjerg, and from 173 to 250 μg N m −2 d −1 at Foulum. A multiple linear regression analysis showed inter-seasonal variations in emissions ( P < 0.001), but annual N 2O emissions from organic and conventional systems were not significantly different despite the lower N input in organic rotations. The annual emissions ranged from 54 to 137 mg N m −2, which corresponded to 0.5–0.8% of the N applied in manure or mineral fertilizer. Selected soil attributes were monitored to support the interpretation of N 2O emission patterns. A second multiple linear regression analysis with potential drivers of N 2O emissions showed a negative response to soil temperature ( P = 0.008) and percent water-filled pore space (WFPS) ( P = 0.052) at Foulum. However, there were positive interactions of both factors with NO 3-N, i.e., high N 2O emissions occurred during periods when high soil nitrate levels coincided with high soil temperature ( P = 0.016) or high soil water content ( P = 0.056). A positive effect ( P = 0.03) of soil temperature was identified at Flakkebjerg, but the number of soil samplings was limited. Effects of cropping system on N 2O emissions were not observed.

Subsoil improvement in a tropical coarse textured soil: Effect of deep-ripping and slotting

In many coarse textured soils, limited root development and biomass production are attributed to adverse physical conditions in the subsoil. The current study was undertaken on an Arenic Acrisol located in Northeast Thailand (i) to assess whether subsoil physical characteristics influence crop rooting depth, and (ii) to compare the benefits associated with conventional tillage with that of localised subsoil loosening on crop performance and selected soil attributes. Control plots consisted of disk ploughing; the implemented treatments were conventional deep-ripping and localised slotting below the planting line. A crop rotation consisting of a legume followed by maize was established annually to assess the impact of these treatments on crop performance. In the control treatment, root development was restricted to the topsoil (0–20 cm) due to high subsoil bulk density (>1.6 Mg m −3). After deep-ripping, no improvement was observed in bulk density, rooting depth and in crop performance. The implementation of a slotting treatment systematically improved root development in the slotted subsoil, root impact frequency increasing from <0.2 to 0.6–0.8 ( P = 0.01) despite no change in the bulk densities of the subsoil. This systematic improvement in root development could be explained by (i) reduced slumping that enable root development prior to recompaction and/or (ii) preferential drainage in the slot and therefore decreased resistance to root penetration. In a dry year maize yield was improved by 78% ( P = 0.01); the deep-rooting legume Stylosanthes was tested only a wet year and its biomass production increased by >40% ( P = 0.03). This study highlights the detrimental impact of subsoil compaction on root development and the potential role of slotting in coarse textured soils as a long-term management tool in addressing adverse subsoil physical characteristics that limit deep-rooting.

A Survey of Soil Attributes in North Dakota by Landscape Position

Land surveys of soil attributes can provide valuable information on the geographic distribution of important soil attributes and summarize the levels found. Landscape position can have a major influence on soil attributes. Consideration of field landscape variables in selecting sampling locations and interpreting results, even in large‐scale surveys, should help to reduce unexplained variability in many soil attributes. We report the results of a survey of selected soil attributes in agricultural fields across North Dakota at sites selected within each field by landscape position. Our objective was to determine if this sampling design might contribute to a better understanding of the distribution of soil attributes. Soils from two or three fields within each of the 53 counties of North Dakota were sampled in 1996. Within each field, three samples of surface soil (0–15 cm) were obtained. One sample was collected from an upland position, one from a slope, and one from a depression. Each field was georeferenced using a differentially corrected GPS receiver. The samples were analyzed for DTPA (diethylenetriaminepentaacetic acid)‐extractable Cu, Zn, and Cd; water soluble B and Se; and soil pH. Mapping and analysis showed distinct regional patterns of all soil factors. Some soil attributes, including pH and extractable Zn, Cu, and Cd, exhibited a strong relationship to field landscape position, while soluble B and Se were less related. The results suggest that separating field sampling locations into upland, sloping, and depressional areas will reduce the confounding effects of field landscape position on larger‐scale spatial trends in soil attributes.

Variabilidade espacial de perdas de solo, do potencial natural e risco de erosão em áreas intensamente cultivadas

O objetivo desta pesquisa foi identificar a variabilidade espacial do potencial natural de erosão, das perdas de solo e do risco de erosão em duas áreas intensamente cultivadas, com o intuito de fornecer subsídios na descrição de padrões de ocorrência de erosão. O solo da área, localizado em Monte Alto, SP, foi classificado como Argissolo Vermelho Amarelo (PVA), relevo ondulado e sob diferentes manejos. O solo da área localizado em Jaboticabal, SP, foi classificado como Latossolo Vermelho (LV), relevo suave, cultivado com cana-de-açúcar. O esquema de amostragem constituiu em uma malha irregular. Amostras de solo foram obtidas na profundidade de 0-0,2 m, para cada malha: 88 amostras para a área de Monte Alto (1465 ha) e 128 amostras para a área de Jaboticabal (2597 ha). Para obtenção dos valores das variáveis estudadas, empregou-se a EUPS para cada ponto amostrado. Os dados foram submetidos à análise estatística descritiva e geoestatística para definição dos semivariogramas. Para os modelos foi utilizada a interpolação por krigagem. Observou-se a ocorrência de dependência espacial para todas as variáveis. O solo PVA apresentou maiores riscos de erosão, devido ao relevo, uso atual e manejo, comparado com o solo LV.

Effect of Wavelength Range on the Measurement Accuracy of Some Selected Soil Constituents Using Visual-Near Infrared Spectroscopy

The wavelength range is one of the main components affecting the measurement accuracy with visible (vis) and near infrared (NIR) spectroscopy. The performance of two commercially-available spectrophotometers with different wavelength ranges for measurement of selected soil attributes was evaluated. The two spectrophotometers considered were a diode array with a short wavelength range (SWR) of 300–1700 nm and a combination of diode array and scanning monochromator with a full wavelength range (FWR) of 350–2500 nm. Scanning was performed on wet-fresh ( in situ conditions) and dry-processed (laboratory conditions) soil samples, to estimate the effect of moisture content on the performance of the two spectrophotometers. Partial least squares (PLS) regression with the leave-one-out cross validation technique was used to develop calibration models relating soil spectra with chemical attributes. Results showed that under wet field soil conditions pH, available phosphorus (P), cation exchange capacity (CEC), potassium (K) and calcium (Ca) were more accurately predicted with the SWR, whereas total nitrogen (N), total carbon (C), sodium (Na) and magnesium (Mg) were better predicted with the FWR. The significant effect of the water absorption at a wavelength of 1950 nm which created considerable changes in the shape of spectra and subsequently loss of important information available at wavelengths greater than 2000 nm, reduced the efficiency of the FWR instrument. The dry soil conditions led to a superior performance of the FWR instrument over the SWR instrument for measurement of all soil attributes. This suggests that a greater wavelength range than 1700 nm is not useful for improving the measurement accuracy of soil attributes (except N and C) with vis-NIR spectroscopy when measurement is to be carried out in the field under wet conditions.

Carbon and N mineralization as affected by soil cultivation and crop residue in a calcareous wetland ecosystem in Central Iran

Mineralization of soil organic matter plays a key role in supplying nutrient elements essential to plant growth. Soil cultivation and crop residue affect C mineralization and nutrient availability in wetland ecosystems. This study evaluated the combined impacts of soil cultivation and crop residue on C and N mineralization in a calcareous wetland soil (Luvic Calcisol) in Central Iran. Soil samples were collected from 0 to 15 cm depth in cultivated and uncultivated plots and analyzed for selected soil attributes. Wheat (Triticum aestivum L.) and alfalfa (Medicago sativa L.) residues were collected and analyzed for the chemical composition. Nitrogen and C mineralization rates were studied using laboratory incubations for 60 days. Results show that in this calcareous wetland soil, cultivation decreased soil total organic carbon and total N contents, while total organic carbon/total N ratio, bulk density, pH, and extractable P and available K levels remain unaffected. Cultivation resulted in a significant increase in soil C and N mineralization. Wheat residue had a significantly lower quality than alfalfa residue, and therefore decomposed more slowly. Results also indicate that plant residue has a significant impact on decomposition rate and nutrient cycling. Soil cultivation and residue quality had a significant influence on C and N cycling and nutrient contents. The combined effects of soil cultivation and crop residue play a significant role in changing the nutrient balance and availability in calcareous wetland soils with conventional agricultural practices. In summary, significant differences occurred in soil attributes and residue decomposition affecting C and nutrient dynamics, and therefore crop productivity.

EDS/SEM study on microaggregates of Brazilian Latosols, in relation to P adsorption and clay fraction attributes

Little has been published on the diversity and importance of microaggregates in tropical latosols and their chemistry and fertility. This study presents a detailed analytical and submicroscopical characterization of microaggregates in selected Brazilian Latosols, representing all latosols orders, by means of electron microprobe and scanning electron microscopy (SEM) at high magnification. Chemical data for microaggregates were related to selected soil attributes, including P sorption. In these latosols, no chemical/mineralogical gradients exist between the different plasma zones of the aggregates, indicating an absence of physical–chemical microaggregate nucleation. The microgranular structure occurs in all latosol Bw horizons, with varying degrees of organization, from ‘strongly developed’ to ‘moderately developed’, varying from discrete micropeds to weakly defined /coalesced micropeds, the latter forming a massive kaolinitic groundmass. The P adsorption capacity (PAC) of the soil was significantly correlated with Al 2O 3 in both external and internal aggregate zones, whereas no correlation was found between PAC and SiO 2, and Fe 2O 3 amounts. The PAC was attributed to both well-crystalline and poorly crystalline Al forms. The EDS/SEM data for the clay plasma are consistent with the results of H 2SO 4 extraction. Regarding EDS analysis of microaggregates, it is shown that soil thin sections of 18 cm 2 sizes adequately represent the soil composition in deeply weathered, mineralogically monotonous Brazilian latosols. Due to its differential distribution between coarse and fine fractions, Ti amounts obtained by EDS and H 2SO 4 are poorly correlated. Ti-EDS data of soil plasma only determines microcrystalline anatase whereas Ti–H 2SO 4 also includes Ti in sand size resistant minerals in the coarse fractions, not selected for EDS analysis in our procedure. The highly weathered latosols studied possess Bw horizons with a pedobiological microgranular structure, whose degree of development and aggregate roundness are influenced by soil mineralogy. At the microaggregate scale, quartz grains, Ti-minerals, charcoal particles, Fe and gibbsite nodules or concretions occur randomly distributed within the clay plasma, as skeletal grains or inclusions.

Spatial and temporal woodland patterns along the lower Turkwel River, Kenya

AbstractSpatial and temporal patterns of riverine woodlands in arid regions of Africa are poorly documented despite their considerable conservation value. We studied 1540 ha of riverine woodland in the lower Turkwel River floodplain, Kenya, between 1990 and 1998. Forty‐one woodland patches were mapped and their soil physical and chemical characteristics, tree species diversity, woody cover, tree density, wood volume and woodland regeneration were determined. The riverine woodland comprised nine vegetation types and a total of 14 woody species. Woodland patch mosaics were associated with microtopographical features and selected soil attributes. The most important woody species were Hyphaene compressa H. Wendl., Acacia tortilis (Forssk.) Hayne and Cadaba rotundifolia Forssk. The exotic Prosopis chilensis (Mol.) St. was invading parts of the riverine woodland. Overall, woody species diversity was low compared to similar riverine woodlands in East Africa. Tree density, wood volume and woody plant regeneration declined over the 8‐year study period, while woody cover was unchanged. Reduced tree density, wood volume and regeneration of woody species might be linked to changes in river flood patterns following the impoundment of the Turkwel Gorge Dam. It is suggested that spatially heterogeneous and temporally stochastic regeneration events, together with occasional tree mortality caused by channel abandonment, create the complex pattern of woodland patches in the lower Turkwel River floodplain. The mapped woodland patches may serve as monitoring units, which in future could reveal the interplay between changes in flooding patterns as a result of dam impoundment, anthropogenic disturbance and the well‐being of the riverine woodlands.

Physical and chemical properties of a Hong Kong roadside soil in relation to urban tree growth

Tree planting in urban areas faces many limitations that suppress performance and increase management burdens. Soil problems are increasingly recognized as an important cause of establishment failures and declines. Recent citygreening programs in Hong Kong necessitate a better understanding of soil difficulties, but relevant information is lacking. A detailed study of physical and chemical properties of a representative roadside soil provides baseline data on edaphic restrictions and hints for correction and amelioration. The soil depth is inadequate for normal root expansion of trees, is excessively stony and sandy, and is beset by poor structure and heavy compaction. Root growth is likely to be restricted by the low levels of porosity and high shear strength. The densely packed surface layer reduces aeration and water movement into the lower layers. The nutrient stock is meager, and the ability to hold available moisture and nutrients is very limited. Soil reaction comparing with local natural soil is uncharacteristically alkaline with pH reaching 8.5 which may induce iron and manganese deficiency. Heavy metals register elevated concentrations especially for lead and zinc, but do not attain phytotoxic levels. The common multiple substrate problems need to be addressed properly before trees are planted. Evaluation of selected soil attributes is advocated for all planting sites.