Variability Of Soil Chemical Properties Research Articles

Variations in soil chemical properties, microbial biomass, and faunal populations as related to plant functional traits, patch types, and successional stages at Sokolov post-mining site - A case study

The majority of studies that investigate plant functional trait effects on ecosystem properties use traits obtained from databases. However, we know little regarding their explanatory power proportionate to that of the semi-quantitative vegetation properties, and much less still is known when considering their temporal changes in a chronosequence. We determined whether soil chemical and biological properties were associated with plant functional traits, observed vegetation properties (“patch type” = bare soil, grassy, woody), and site age (10, 18, 28, and 55 years), at four spontaneously overgrown post-mining locations in the Czech Republic. Abiotic soil properties were expected to be closely related to the site age, while above and below ground macrofauna (epigeic and endogeic, respectively), mesofauna, and microbial biomass were expected to be related to the plant functional traits and patch types. Site age and plant functional traits were more important explanatory factors for most of the chemical, microbial, and macrofaunal soil properties than the patch types. Patch type was the only plant-related factor capable of explaining the mesofauna community variations. Epigeic macrofauna were found to correlate more strongly with the plant functional traits than endogeic macrofauna. The abundance of most fauna correlated positively with an increase in plant cover and litter input and was significantly higher in vegetated patches and old sites.

Spatial Variation of Soil Chemical Properties in Industrial Wastewater Contaminated Paddy Soil

Soil quality is essential for sustainable crop production. Excessive or deficient in necessary chemical elements in soil is a concern for soil quality. The study was undertaken to evaluate the impact of chemical industrial wastewater on chemical properties of soil and observe spatial distribution of nutrients in paddy soil adjacent to a chemical industry. A command area comprising a paddy field exposed to a chemical industrial wastewater was selected to study and 10 composite soil samples including a control (not exposed to wastewater) was collected and analyzed. Compared to background values soil pH, OC, N, P, Ca, and S were found higher in contaminated soils through the industrial wastewater. The order of the increment of the nutrients in the contaminated soil was as N>P>S>OC>Ca>Na. Sulphur and Nitrogen pose as potent elements for toxicity or pollution of the soil exposed to untreated wastewater. Differential spatial variations were observed for various nutrients in the area. Highest spatial variation was observed for S, N and B followed by P, K, Ca, Mg and Na might be due to anthropogenic activities through industrial untreated wastewater. These issues need to be taken into consideration while recommending fertilizers for crops grown in this type of command area.J. Environ. Sci. & Natural Resources, 9(2): 85-90 2016

Short-range and regional spatial variability of soil chemical properties in an agro-ecosystem in eastern Croatia

Spatial and temporal characterization of soil properties in agro-ecosystems is crucial for monitoring the evolution of soil functions and for understanding the main influential processes. Moreover, the objective mapping of soil properties in agro-ecosystems is urgently needed for regional planning purposes and the proper choice of land management practices. In this work, the geostatistical analysis of a dataset of soil properties, derived from 2411 soil samples collected in Vukovar-Srijem County (Croatia), highlighted the multiple benefits of a spatial-statistical approach. The main aim of this paper is to jointly examine short-range (i.e., within-field) and regional spatial variability of several soil chemical properties: soil pH, organic matter (OM), plant available phosphorus (AP) and potassium (AK). The available sampling network, characterized by a set of 2411 (0–30cm depth) irregularly and field-clustered soil samples, allowed to derivate of two typologies of soil nutrient maps by means of ordinary block kriging: within-field high-resolution maps (block size 250m) and regional low-resolution maps (block size 2000m). Soil pH and OM had lower variability compared to AP and AK. The OM content and pH ranged from 1.24% to 5.25% and from 3.69 to 7.84, respectively. Almost 94% of all samples had an OM content below 3%, indicating the need for future adoption of environmentally friendly soil management in this county. The mean values of AP and AK were 173mgkg−1 and 238mgkg−1, respectively, indicating a moderate supply of these nutrients. Geostatistical analysis revealed that the best-fit models were spherical for pH and AP, with moderate spatial dependency, and exponential for OM and AK, with strong spatial dependency. The within-field high-resolution soil property maps can be used as guidance for site-specific fertilization and liming. In addition, the regional maps derived for larger interpolation support provide quantitative information for regional planning and environmental monitoring and protection purposes. Consequently, the multi-resolution mapping of soil properties and the analysis of their spatial variability highlighted possible connections with influential factors and processes, including the relationships with different soil types. Finally, quantification of the spatial variability of soil properties by means of variogram models constitutes a basis for optimizing soil sample spacing for mapping purposes in the studied region.

Earthworm population and microbial activity temporal dynamics in a Caspian Hyrcanian mixed forest

Few studies have analyzed how tree species within a mixed natural forest affect the dynamics of soil chemical properties and soil biological activity. This study examines seasonal changes in earthworm populations and microbial respiration under several forest species (Carpinus betulus, Ulmus minor, Pterocarya fraxinifolia, Alnus glutinosa, Populus caspica and Quercus castaneifolia) in a temperate mixed forest situated in northern Iran. Soil samplings were taken under six individual tree species (n = 5) in April, June, August and October (a total of 30 trees each month) to examine seasonal variability in soil chemical properties and soil biological activity. Earthworm density/biomass varied seasonally but not significantly between tree species. Maximum values were found in spring (10.04 m−2/16.06 mg m−2) and autumn (9.7 m−2/16.98 mg m−2) and minimum in the summer (0.43 m−2/1.26 mg m−2). Soil microbial respiration did not differ between tree species and showed similar temporal trends in all soils under different tree species. In contrast to earthworm activity, maximum microbial activity was measured in summer (0.44 mg CO2–C g soil−1 day−1) and minimum in winter (0.24 mg CO2–C g soil−1 day−1). This study shows that although tree species affected soil chemical properties (pH, organic C, total N content of mineral soils), earthworm density/biomass and microbial respiration are not affected by tree species but are controlled by tree activity and climate with strong seasonal dynamics in this temperate forest.

ANÁLISE DA VARIABILIDADE ESPACIAL DOS ATRIBUTOS QUÍMICOS DO SOLO NA REMOÇÃO DE NUTRIENTE E DA PRODUTIVIDADE DA BRACHIARIA HUMIDICULA UTILIZADA EM RAMPAS DE ESCOAMENTO SUPERFICIAL NO TRATAMENTO DE ESGOTO SANITÁRIO OPERANDO EM CONDIÇÕES REAIS

No Brasil, o sistema de tratamento de esgoto em rampas de escoamento superficial foi implantando por algumas companhias de saneamento por ser considerado de baixo custo e apresentar eficiência de tratamento semelhante ou superior às obtidas pelos métodos convencionais, desde que seja manejado adequadamente. Este trabalho foi desenvolvido com o objetivo de avaliar a variabilidade espacial dos atributos químicos do solo, a remoção de nutrientes e a produtividade da gramínea Brachiaria humidicula, cultivada em rampa de escoamento superficial no tratamento de esgoto sanitário. O sistema funciona no município de Januária-MG, a rampa recebe efluente oriundo de um reator anaeróbio de fluxo ascendente (RAFA), precedido de tratamento preliminar (gradeamento). Foram coletadas 24 amostras de solo e de tecido vegetal em uma malha montada sobre as rampas. A partir das amostras de solo, determinou-se o pH, a condutividade elétrica (CE), a razão de adsorção de sódio (RAS), o percentual de sódio trocável (PST) e os teores de matéria orgânica (MO), fósforo (P), potássio (K), cálcio (Ca), magnésio (Mg), sódio (Na), ferro (Fe), zinco (Zn,) e cobre (Cu). Nas amostras de tecido vegetal determinou-se a produtividade de matéria fresca e seca e a remoção de nitrogênio (N), P e K. Observou-se elevada variação espacial da produtividade, onde o valor médio encontrado de matéria fresca e seca foi de 84 e 14 t ha-1, respectivamente. Os macronutrientes analisados, P e K, apresentaram valores médios de 577,6 e 23,9 mg dm-3, respectivamente. As maiores concentrações dos elementos Na, K, Zn, Mn, Mg, Ca, Fe e Cu foram obtidas nas regiões centrais da área, o que pode indicar um possível caminho preferencial do efluente. A remoção média de N, P e K foi de aproximadamente 360, 65 e 430 t ha-1, respectivamente.

Trade-offs and spatial variation of functional traits of tree species in a subtropical forest in southern Brazil

Plant functional traits have been recognized as important factors related to the ecological strategies of species in forest ecosystems. We examined the relationships between functional traits and both tree species performance and environmental conditions in a subtropical forest in Brazil. Over four years (2008-2012), we investigated how demographic rates were related to functional traits (wood density, leaf area and tree height) of 20 species sampled within 50 plots of 10 × 20 m, which had previously evaluated as to environmental conditions. Non-metric multidimensional scaling was used to order the species by their functional traits. The demographic rates were fit a posteriori to the ordination, with significant rates (p < 0.05) plotted as vectors. The relationships between environmental conditions and the community-weighted means (CWMs) of trait values were verified using redundancy analysis. CWM wood density was positively correlated with soil pH. CWM leaf area and CWM maximum tree height were both negatively correlated with altitude and positively correlated with soil magnesium (Mg) content. The taller species with lower wood density, which occupied the forest canopy, had a greater diameter increment and lower recruitment than did the shortest species with higher wood density. The shorter species with higher wood density, which occupied the understory, had greater recruitment and a greater increase in abundance than did the taller/lower-wood-density species. Our study (i) revealed changes in the forest related to the light environment, with an increase in the relative participation of shade-tolerant species with higher wood densities, and (ii) detected small-scale spatial variation in community traits as a response to variations in soil chemical properties and topography.

Assessment of Soil Chemical Properties and Rice Yield in Tidal Submergence Ecosystem

Spatial variability of soil chemical properties is critical for improving rice productivity and sustainable farming techniques. However, a systematic assessment on the spatial variability of tidal ecosystem has not been conducted. So, 144 soil samples were collected across Barisal, Borguna and Jalkhati districts and analyzed for six common chemical properties. Rice yield data was obtained by surveying farmers during crop harvest. Soil parameters and rice yield varied considerably throughout the study areas and their coefficients of variation ranged from 8.77 to 71.04%. Slight variability was observed for soil organic matter (SOM) and available K. The pH of the soils was slightly acidic to alkaline. These paddy fields were characterized by high concentrations of SOM, available P, K and S; but low total N. Rice yield was significantly and positively correlated with pH, available K and S, but negatively correlated with SOM.Bangladesh Agron. J. 2015, 18(2): 79-87

Spatial Variability in Soil Properties of Mango Orchards in Eastern Plateau and Hill Region of India

Spatial Variability in Soil Properties of Mango Orchards in Eastern Plateau and Hill Region of India Analysis and interpretation of spatial variability of soil chemical properties is important in framing site-specific fertilizer management practices for mango orchards. This paper aims to study the spatial structure of soil variables in the mango orchards in the eastern plateau region of India. Soil samples were collected from 90 points across the mango orchards from three soil horizons (0-30, 30-60 and 60-90cm). Eleven soil properties were analysed by classical statistical and geo-statistical methods. Soil pH exhibited the lowest statistical variation (CV<15%) while it was highest (CV 68.4 to 97.8%) for the phosphorous (P) content in all the soil layers. Spherical, Gaussian and Exponential semivariogram models were developed after accounting for necessary transformations. The findings of geostatistical analysis showed that spatial structures exist in the soil variables. In surface layers, soil pH, phosphorous (P), iron (Fe), calcium (Ca) and copper, (Cu) have the strong spatial dependence with nugget-sill ratios of less than 25%. Analysis suggested that both the internal and external factors are responsible for the spatial dependence of the soil properties. The magnitude and the pattern of spatial variability in soil chemical properties have implications for variable rate fertilizer application strategies in the mango orchards of the eastern region.

Sistemas de preparo do solo e de semeadura no rendimento de grãos de soja em área de várzea

RESUMO: A presença de camada compactada próxima à superfície do solo e a variabilidade das propriedades químicas do solo podem afetar o rendimento de grão de soja. Com o trabalho, objetivou-se avaliar a influência de sistemas de preparo do solo e de semeadura e de locais de cultivo (áreas de corte e aterro) no rendimento dessa cultura. O experimento foi realizado na área experimental de várzea da Universidade Federal de Santa Maria, nas safras 2013/14 e 2014/15. O delineamento foi blocos ao acaso, com quatro repetições. Os tratamentos foram arranjados em parcelas subdivididas. As parcelas principais foram: área de corte (A1) e área de aterro (A2). As subparcelas foram os tipos de preparo do solo e de semeadura: com escarificação do solo e semeadura utilizando disco duplo na semeadora (D1); sem escarificação do solo e semeadura utilizando haste sulcadora na semeadora (D2); sem escarificação do solo e semeadura utilizando disco duplo na semeadora (D3). A cultivar utilizada foi a BMX Tornado. O tratamento com escarificação e haste sulcadora reduziu a resistência do solo à penetração e proporcionou maior teor de Mg e S no tecido foliar na safra 2013/14; e de N, P, K, Ca, Mg e S, em 2014/15. Esse tipo de preparo de solo possibilita maior rendimento de grão de soja sem diferenças entre as áreas de corte e de aterro.

Assessment of the spatial variability of soil chemical properties along a transect using multifractal analysis

The spatial variability of soil properties can be assessed through concepts of scale invariance, fractals and multifractals. The aim of this study was to characterize the scaling patterns and structural heterogeneity properties of general soil chemical properties along a short (i.e. 52 m large) transect. Field measurements were carried out at the experimental farm of CIAM located in Mabegondo, A Coruña, Spain. The studied transect was marked following land slope, and 66 soil samples were collected at the 0-20 cm depth every 0.8 m. The soil properties analyzed were: pH (H2O ), organic carbon content, exchangeable Ca, Mg and K, exchangeable acidity (H + Al), exchangeable bases (SB), cation exchange capacity (CEC), percent base saturation (V) and extractable P. The soil properties studied showed various degrees of multifractality. The spatial distribution of pH was characterized by quasi-monofractal behaviour; CEC, (H+Al) and OM, presented a relatively low degree of multifractality, and the other soil properties studied showed stronger degrees of multifractality, being the highest one for Olsen extractable P. In general, the scaling features of the properties studied implied a multifractal nature, where the low and high density regions scaled differently.

Variabilidade Espacial de Atributos Químicos de Solo Sob Pastagem

The objective of this study was to analyze the spatial variability of soil chemical attributes under pasture, as well as lime and fertilizer recommendations based on the interpretation of soil chemical analysis from two sampling methods: conventional and systematic depths of 0 to 10 and 10 to 20 cm. The study was conducted at IFES-campus Alegre-ES. Data analysis was performed using descriptive statistics and geostatistics. Results indicate that the spatial method enabled the identification of deficit areas and excessive liming and fertilization, which could not be defined by the conventional method.

USE OF SCALED SEMIVARIOGRAMS IN THE PLANNING SAMPLE OF SOIL CHEMICAL PROPERTIES IN SOUTHERN AMAZONAS, BRAZIL

The lack of information concerning the variability of soil properties has been a major concern of researchers in the Amazon region. Thus, the aim of this study was to evaluate the spatial variability of soil chemical properties and determine minimal sampling density to characterize the variability of these properties in five environments located in the south of the State of Amazonas, Brazil. The five environments were archaeological dark earth (ADE), forest, pasture land, agroforestry operation, and sugarcane crop. Regular 70 × 70 m mesh grids were set up in these areas, with 64 sample points spaced at 10 m distance. Soil samples were collected at the 0.0-0.1 m depth. The chemical properties of pH in water, OM, P, K, Ca, Mg, H+Al, SB, CEC, and V were determined at these points. Data were analyzed by descriptive and geostatistical analyses. A large part of the data analyzed showed spatial dependence. Chemical properties were best fitted to the spherical model in almost all the environments evaluated, except for the sugarcane field with a better fit to the exponential model. ADE and sugarcane areas had greater heterogeneity of soil chemical properties, showing a greater range and higher sampling density; however, forest and agroforestry areas had less variability of chemical properties.

A simple assessment on spatial variability of rice yield and selected soil chemical properties of paddy fields in South China

Data related to the spatial variability of properties of paddy soil is critical for improving rice productivity and designing sustainable farming techniques. However, a systematic assessment focusing on the spatial variability of low-yield paddy soil has not been conducted in South China. In this context, 560 soil samples were collected across South China and analyzed for nine common chemical properties. Rice yield data was obtained by surveying farmers during soil sampling. Soil parameters and rice yield varied considerably throughout the study area and their coefficients of variation ranged from 17.3% to 74.2%. Experimental semivariograms were developed and a moderate spatial dependence was observed for all selected parameters. Distribution maps, derived by kriging interpolation, illustrated that these paddy fields were characterized by high concentrations of soil organic matter (SOM), total N (TN), available N (AN) and available Zn (AZn); pH values decreased widely comparing with the data reported by the National Soil Survey, especially in southeast China; the areas with low soil P concentrations (<10mgkg−1) were mainly located in southwest China; cation exchange capacity (CEC), available K (AK) and available Si (ASi) had similar trends in spatial distributions with high concentrations in southeast China and low concentrations in southwest. Notably, paddy fields in southeast China were typically deficient in AK due to their concentrations, all of which are almost less than 100mgkg−1. Correlation analysis revealed that rice yield was significantly positively correlated with pH, CEC, AK and ASi, while negatively correlated with AN and AZn. Low pH, AK, CEC and ASi levels may be the most important constraints limiting rice productivity and fertilizers with N and Zn may be over-used and must be applied appropriately. The soil quality index (SQI) was also calculated using the analyzed chemical properties and a significant correlation was observed between SQI and rice yield, supporting earlier findings that good soil chemical health is essential for optimum sustained crop production. The remarkable variations of SQI and rice yield indicated that the potential for increasing rice productivity is a real prospect. Therefore, regional planning fertilization should pay more attention to the spatial variability of soil chemical properties to avoid economic losses and environmental pollution, and especially to the limited nutrients.

Variabilidade espacial dos atributos químicos do solo, associada ao microrrelevo

A variabilidade dos atributos químicos do solo é influenciada por complexas interações entre os fatores e os processos de formação do solo. Este trabalho partiu da hipótese de que os atributos químicos do solo variam com o microrrelevo a ponto de alterar as recomendações de manejo para uso agrícola. Com isto, o relevo foi separado em compartimentos e as superfícies estudadas com o objetivo de se determinar os atributos químicos do solo, avaliar a distribuição e a dependência espacial desses atributos. A grade amostral compreendeu uma área de 102 ha da Fazenda Agrícola Famosa, localizada na Chapada do Apodi, CE. O solo da área apresenta origem calcária e as amostras foram coletadas em 92 pontos distanciados 200 m na linha e 100 m entre linhas, nas profundidades de 0-20 e 20-40 cm. Com os dados, gerou-se um modelo de elevação do terreno e, com base nas formas de relevo identificadas, dividiu-se o local de estudo em superfícies. Os dados foram avaliados por estatística descritiva e análise de variabilidade espacial, com base no ajuste de semivariogramas e mapas de krigagem. Os atributos químicos do solo apresentaram variabilidade espacial nos microrrelevos convexo, retilíneo e côncavo, intensificada pelo fluxo de água nas profundidades.

Spatial variability of soil chemical attributes and productivity and the chemical and physical properties of oranges

The purpose of this study was to analyze the spatial variability of soil properties and productivity and the chemical and physical properties of oranges (Monte Parnaso variety) in their geographical quadrants. This experiment was conducted in a commercial orange orchard in the municipality of Nova Laranjeiras in the State of Parana, Brazil. A GPS receiver and a total station were used to measure the spatial location of the fruit and to determine which quadrant they were located in. In this experiment, 13 trees were studied. Twelve fruits were evaluated in each geographical quadrant, and 156 fruits were considered. After harvest, the productivity was expressed as kg per quadrant (kg quadrant -1 ). Next, physical tests (equatorial diameter (EqD), total fruit mass (TFM), juice yield (JY)) and chemical tests (total soluble solids (TSS), total titrable acidity (TTA), the TSS/TTA ratio, and the ascorbic acid (AA) content) were conducted in the laboratory. In addition, the data were subjected to analysis by descriptive statistics and geostatistics to determine the spatial variability of the physical and chemical properties of the oranges, the variations of the soil properties and the correlations between the following parameters: the pH properties of the fruit and Zn; TFM and K; EqD and K, and C and TSS. The orchard varies spatially, especially regarding the EqD, TFM, JcP, TSS and AA for the quadrants with the highest values (the Northwest, Southeast, Northeast, Southwest and Southeast, respectively). The soil potassium and zinc contents were strongly correlated with the physical and chemical properties of the orange fruits. El objetivo de este estudio ha sido analizar la variabilidad espacial de los atributos del suelo, de la productividad y de las propiedades fisicas y quimicas de los frutos de la variedad de naranja Monte Parnaso, en relacion a los cuadrantes geograficos en que se ubican los frutos analizados. El experimento se realizo en un huerto comercial de naranjos en Nova Laranjeiras, Estado de Parana, Brasil. En el procedimiento de georreferenciacion de la area y de cada arbol de la muestra, se utilizo un GPS y una estacion total para medir la localizacion espacial de la fruta y luego la definicion de que cuadrante se ubicaban. En el experimento, se utilizaron 13 arboles en las cuales se analizaron tres frutas por cuadrante geografico de cada arbol, por un total de 156 frutas. Despues de la cosecha se estimo la productividad en kg cuadrante -1 y en el laboratorio fueran realizados analisis fisica (diametro ecuatorial (ED), masa total de la fruta (MT), rendimiento de jugo (RS)) y quimicos (solidos solubles totales (SST), acidez titulable (AT), relacion SST/AT y acido ascorbico (AA)) de la fruta. Los datos fueron sometidos a analisis de la estadistica descriptiva y de la geoestadistica senalando la variabilidad espacial de las propiedades fisico-quimicas de las naranjas y los atributos del suelo y tambien correlacion entre los atributos de la fruta pH y Zn, MT y K, ED y K y finalmente SST y C. El huerto tiene variaciones espaciales principalmente para los atributos diametro ecuatorial, masa total de la fruta, rendimiento del jugo, SST y acido ascorbico, siendo los cuadrantes con mayores valores fueron, respectivamente, noroeste, sureste, noreste, suroeste y sureste. Especialmente potasio y zinc, las propiedades del suelo, fuertemente correlacionados con las propiedades fisicas y quimicas de las frutas de color naranja.

Spatial variability of soil chemical attributes and productivity and the chemical and physical properties of oranges

Spatial variability of soil chemical attributes and productivity and the chemical and physical properties of oranges

Artificial neural network modeling of microbial community structures in the Atlantic Forest of Brazil

Microbial communities vary across the landscape in forest soils, but prediction of their biomass and composition is a difficult challenge due to the large numbers of variables that influence their community structures. Here we examine the use of artificial neural network (ANN) models for extraction of patterns among soil chemical variables and microbial community structures in forest soils from three regions of the Atlantic Forest of Brazil. At each location, variations in soil chemical properties and FAME profiles of microbial community structures were mapped at 20 × 20 m intervals within 10 ha parcels. Geostatistical analyses showed that spatial variability in soil physical and chemical variables could be mapped at scale distances of 20 m, but that FAME profiles representing the microbial communities were highly variable and had no spatial dependence at the same scale in most cases. RDA analysis showed that FAME signatures representing different microbial groups were positively associated with soil pH, OM, P and base cations concentrations, whereas microbial biomass was negatively associated with the same environmental factors. In contrast, ANN models revealed clear relationships between microbial community structures at each parcel location, and generated verifiable predictions of variations in FAME profiles in relation to soil pH, texture, and the relative abundances of base cations. The results suggest that ANN modeling provides a useful approach for describing the relationships between microbial community structures and soil properties in tropical forest soils that were not able to be captured using geostatistical and RDA analyses.

An application of PCA and fuzzy C-means to delineate management zones and variability analysis of soil

Within-field variability is a well-known phenomenon and its study is at the centre of precision agriculture (PA). In this paper, site-specific spatial variability (SSSV) of apparent Electrical Conductivity (ECa) and crop yield apart from pH, moisture, temperature and di-electric constant information was analyzed to construct spatial distribution maps. Principal component analysis (PCA) and fuzzy c-means (FCM) clustering algorithm were then performed to delineate management zones (MZs). Various performance indices such as Normalized Classification Entropy (NCE) and Fuzzy Performance Index (FPI) were calculated to determine the clustering performance. The geo-referenced sensor data was analyzed for within-field classification. Results revealed that the variables could be aggregated into MZs that characterize spatial variability in soil chemical properties and crop productivity. The resulting classified MZs showed favorable agreement between ECa and crop yield variability pattern. This enables reduction in number of soil analysis needed to create application maps for certain cultivation operations.

The short-term effects of surface soil disturbance on soil bacterial community structure at an experimental site near Scott Base, Antarctica

Humans are visiting Antarctica in increasing numbers, and the ecological effect of rapid soil habitat alteration due to human-induced physical disturbance is not well understood. An experimental soil disturbance trial was set up near Scott Base on Ross Island, to investigate the immediate and short-term changes to bacterial community structure, following surface soil disturbance. Three blocks, each comprising an undisturbed control, and an area disturbed by removing the top 2 cm of soil, were sampled over a time series (0, 7, 14, 21, and 35 days), to investigate changes to bacterial community structure using DNA profiling by terminal restriction fragment length polymorphism. The simulated disturbance did not cause any major shifts in the structure of the bacterial communities over the 35-day sampling period. Ordination showed that the bacterial community composition correlated strongly with soil EC (R 2 = 0.55) and soil pH (R 2 = 0.67), rather than the removal of the top 2 cm of surface material. Although the replicate blocks were visually indistinguishable from one another, high local spatial variability of soil chemical properties was found at the study site and different populations of bacterial communities occurred within 2 m of one another, within the same landscape unit. Given the current knowledge of the drivers of bacterial community structure, that is, soil EC, soil pH, and soil moisture content, a follow-up investigation incorporating DNA and RNA-based analyses over a time frame of 2–3 years would lead to a greater understanding of the effects of soil disturbance on bacterial communities.

Assessment of spatial variability of selected soil chemical properties in a communal irrigation scheme under resource-poor farming conditions in Vhembe District of Limpopo Province, South Africa

An understanding of spatial variability of chemical soil properties is necessary for proper nutrient management. Therefore spatial variabilities of soil pH, P, K, Ca and Mg in communal irrigation scheme under resource-poor farming conditions were determined. A total of 230 soil samples were collected from two soil depths (0 to 30 and 30 to 60 cm) at 100 m grid intervals. Basic statistics and geostatistical analyses of the data were performed using SAS 9.0 and GS+ 9, respectively. Soils showed high variabilities for all variables that were analyzed. Soil pH exhibited the lowest CV (6.0%) for both layers whereas all other measured variables displayed high CV for both soil layers. Most properties were analyzed by exponential model except for Ca and Mg that were fitted into spherical and Gaussian models respectively. All variables that were fitted into exponential model had strong spatial structure and those fitted into spherical model had a moderate spatial structure. Kriged contour maps displayed positional relationship between the topsoil and subsoil layers. Areas with low K and P can be delineated into separate management zones based on their requirements for these elements. The study showed that geostatistics is a useful tool to map spatial variabilities of soil chemical properties even under resource-poor farming conditions. These maps can be used to encourage/implement variable-rate of input application and inform resource-poor farmers of the benefits of this strategy, thereby reducing variation in soil fertility status caused by application of indiscriminate types and rates of manure and fertilizers. Key words: Site-specific soil management, soil layers, Kriged contour maps, geostatistics, exponential model, South Africa.