Spatial Variability of Cadmium and Lead in Surface Soils in-relation to Landuse and Topography

Accumulation of trace elements in soils has become an environmental concern. Understanding spatial variability of trace elements in relation to point and non-point sources is important to identify threats and monitoring mechanisms. Objectives of this study were to explore the spatial variability of cadmium (Cd) and lead (Pb) in relation to the land-use and topography. One hundred and thirty seven surface soil (0-15 cm) samples were collected from a tropical Ultisol soil scape in up-and mid-country in wet zone in Sri Lanka, representing tea, forest, and urban land uses. Total Cd and Pb concentrations were determined by digesting the soils using aqua regia (Trace-metal grade) and analysed using Graphite Furnace Atomic Absorption Spectrophotometer, following USEPA method 7010.Extractable concentrations of Cd and Pb were determined using Mehlich 3 extraction. Soil pH, electrical conductivity, cation exchange capacity, available P, total P, amorphous Fe, total Fe and Mn were determined using standard methods. Total and Mehlich 3 concentrations of trace elements showed positively skewed data distributions. Across all the land uses, the total Cd and Pb concentrations ranged from 0.05 to 0.40 mg kg-1 (median: Tea=16, Urban=13, Forest=19) and 3 to 37 mgkg-1 (median: Tea=0.13, Urban=0.14, Forest=0.16) respectively. Mehlich 3 Cd and Pb concentrations were low and ranged from 0.01 to 0.62 mgkg-1and 1 to 26 mgkg-1, respectively. Potential bioavailability of Cd in tea, urban and forest land uses was 40%, 32% and 32% respectively, meanwhile for Pb it was 40%, 60% and 40% respectively. Regression analysis explained that the relationship of total Pb and Mehlich 3 extractable Pb concentrations with elevation was significant (p<0.05); However, only about 4-7% of variation of them was explained by elevation. Cd concentration was not significantly related to elevation. Variability of concentrations of Cd and Pb were not related to land use. Soil associations were also not related to spatial variability of total concentrations of Cd and Pb in soils. Spatial variability of total concentrations of Cd and Pb will be presented with maps including land use, soil association and elevation distribution.Keywords: Potential bioavailability, Spatial variability, Topography, Trace element

Bioaccessibility of Lead in Long-Term Vegetable Grown Urban Soil

Vegetable cultivation has been practiced for more than fifty years in the up-country of Sri Lanka providing about 60% of country’s vegetable requirement. Often, vegetable cultivations are distributed in urban areas. Moreover, agricultural inputs, gasoline and paints can contribute for lead (Pb) contamination in soils. Direct soil ingestion is the major exposure pathway of soil Pb to organisms. The risk of direct ingestion of soil Pb can be assessed by using in-vitro bioaccessibility tests. Objectives of the study were to assess bioaccessibility of Pb in long-term vegetable grown urban soils by using in-vitro bioaccessibility tests and to investigate the potential of Mehlich 3 extractable Pb as a measure of bioaccessible Pb. Simplified physiologically based in-vitro extraction test was conducted for extracting bioaccessible Pb in 42 surface soil samples collected from vegetable grown fields located in urban areas in Nuwaraeliya. Total Pb concentrations in soils were determined by digesting the soils using aqua regia (trace metal-grade) and analysing using Graphite Furnace Atomic Absorption Spectrophotometer. Total Pb concentration in soils ranged from 10 to 110 mg/kg. The Mehlich 3 Pb and bioaccessible Pb concentrations were low, which ranged from 2 to 12 mg/kg and 1 to 3 mg/kg, respectively. High available P (47 to 757 mg/kg) and organic C content (1.1 to 3.8%) in soils may have contributed to low bioaccessibility of Pb. The regression analysis revealed that only 44% of variation of bioaccessible Pb and 22% of variation of total Pb can be explained by Mehlich 3 Pb (p<0.001). Effect of total Pb on bioaccessible Pb is low. Strong relationship (p<0.001) was observed between bioaccessible Pb and Mehlich 3 Pb expressed as percentages of total Pb [bioaccessibility of Pb=0.17*(availability of Pb)+0.38, R2=0.71]. Thus, less laborious Mehlich 3 and total Pb measurements can be used to estimate bioaccessibility of Pb. Low bioaccessibility suggested that the risk of direct exposure for soil Pb is minimal in the tested long-term vegetable grown urban soil. Keywords: Lead, Bioaccessibility, Urban soil, Vegetable, Mehlich 3 extractio

Spatial representation of organic carbon and active-layer thickness of high latitude soils in CMIP5 earth system models

AbstractSoil properties such as soil organic carbon (SOC) stocks and active-layer thickness are used in earth system models (ESMs) to predict anthropogenic and climatic impacts on soil carbon dynamics, future changes in atmospheric greenhouse gas concentrations, and associated climate changes in the permafrost regions. Accurate representation of spatial and vertical distribution of these soil properties in ESMs is a prerequisite for reducing existing uncertainty in predicting carbon-climate feedbacks. We compared the spatial representation of SOC stocks and active-layer thicknesses predicted by the coupled Model Intercomparison Project Phase 5 (CMIP5) ESMs with those predicted from geospatial predictions, based on observation data for the state of Alaska, USA. For the geospatial modeling, we used soil profile observations (585 for SOC stocks and 153 for active-layer thickness) and environmental variables (climate, topography, land cover, and surficial geology types) and generated fine-resolution (50-m spatial resolution) predictions of SOC stocks (to 1-m depth) and active-layer thickness across Alaska. We found large inter-quartile range (2.5–5.5m) in predicted active-layer thickness of CMIP5 modeled results and small inter-quartile range (11.5–22kgm−2) in predicted SOC stocks. The spatial coefficient of variability of active-layer thickness and SOC stocks were lower in CMIP5 predictions compared to our geospatial estimates when gridded at similar spatial resolutions (24.7 compared to 30% and 29 compared to 38%, respectively). However, prediction errors, when calculated for independent validation sites, were several times larger in ESM predictions compared to geospatial predictions. Primary factors leading to observed differences were (1) lack of spatial heterogeneity in ESM predictions, (2) differences in assumptions concerning environmental controls, and (3) the absence of pedogenic processes in ESM model structures. Our results suggest that efforts to incorporate these factors in ESMs should reduce current uncertainties associated with ESM predictions of carbon-climate feedbacks

Exploring the Response of Paddy for Varying Levels of Soil Phosphorus in Tropical Soilscapes

Better management of soil Phosphorus (P) in crop cultivation leads to environmental and economic benefits. Proper understanding of the crop response to inherent soil P is important to develop site-specific recommendations. The objective of this study was to assess the yield response of paddy for varying levels of inherent available soil P in Alfisols and Ultisols. Surface soil (0-15 cm depth) P content was measured in 71 paddy fields in three districts of Sri Lanka, namely Anuradapura, Kurunegala and Polonnaruwa. Experiment plots (3x6 m) at each site comprised of ample application of N, P and K and an omission treatment plot of P. Total yield of each plot was recorded at the end of the season. The available P showed a large variability (range=from 2.7 ppm to 34.2 ppm, CV=78%) meanwhile 31% of the experimental sites were below the optimum soil P level for paddy (5 ppm).Omission plot treatments did not show a clear yield response for added P. Very low correlation coefficient between the yield of the omission treatment with the inherent P level (0.05), indicated that inherent P level will not determine the yield. The yield response was plotted against the Olsen P, and very low R2 value (0.03) indicated the Olsen P content does not clearly reflect the actual P requirement in every experimental sites. Short term availability of P from soil reserves cause to mask the effects of spatial variability on yield response and it was concluded that further studies are required to assess P dynamics to take SSNM decisions.Keywords: Paddy, Phosphorus, Site specific nutrient managemen

Estatística multivariada aplicada à diminuição do número de preditores no mapeamento digital do solo

O objetivo deste trabalho foi avaliar a possibildade de se gerar um menor conjunto de preditores não correlacionados e potencialmente aplicáveis ao mapeamento digital de solos, pelo uso da estatística multivariada. Os atributos de terreno, elevação, declividade, distância à drenagem, curvatura planar, curvatura de perfil, radiação relativa disponível, logaritmo natural da área de contribuição, índice de umidade topográfica e capacidade de transporte de sedimento, foram transformados pelo método Varimax nas variáveis: altimetria, hidrologia e curvatura. Essa transformação representou uma concentração de 65,57% da variabilidade dos dados originais nas três novas componentes. As novas variáveis possibilitam o emprego de menor quantidade de dados nos modelos preditivos, além do fato de serem não correlacionados. A rotação Varimax permite que a relação com o ambiente de formação do solo seja explicitamente inserida nos modelos preditivos

Spatial relationships between soil attributes and corn yield in no-tillage system

Soil properties play an important role in spatial variability of crop yield. However, a low spatial correlation has generally been observed between maps of crop yield and of soil properties. The objectives of the present investigation were to assess the spatial pattern variability of soil properties and of corn yield at the same sampling intensity, and evaluate its cause-and-effect relationships. The experimental site was structured in a grid of 100 referenced points, spaced at 10 m intervals along four parallel 250 m long rows spaced 4.5 m apart. Thus, points formed a rectangle containing four columns and 25 rows. Therefore, each sampling cell encompassed an area of 45 m² and consisted of five 10 m long crop rows, in which the referenced points represented the center. Samples were taken from the layers 0-0.1 m and 0.1-0.2 m. Soil physical and chemical properties were evaluated. Statistical analyses consisted of data description and geostatistics. The spatial dependence of corn yield and soil properties was confirmed. The hypothesis of this study was confirmed, i.e., when sampling the soil to determine the values of soil characteristics at similar to sampling intensity as for crop yield assessments, correlations between the spatial distribution of soil characteristics and crop yield were observed. The spatial distribution pattern of soil properties explained 65 % of the spatial distribution pattern of corn yield. The spatial distribution pattern of clay content and percentage of soil base saturation explained most of the spatial distribution pattern of corn yield