Subsoil Samples Research Articles

Soil Carbon Storage Potential of the Home Gardens Adjoining Selected Natural Forests of the Southern Sri Lanka

Conversion of forests to other land uses is inevitable despite the environmental issues associated with forest clearing. Tropical home gardens have long been identified as a land-use system analogous to forests from various perspectives. Carbon storage in the tropical forest soils is estimated to be nearly 32% of the global soil carbon. Although few in number, research conducted in Sri Lanka has shown that the home garden soils could store relatively a large amount of carbon. Present study was conducted in the low country wet zone of Sri Lanka (WL2) using the topsoil (0-15 cm) and subsoil (15-30 cm) samples taken from two sets of home gardens (HG) adjoining two natural forests (Mulatiyana and Wilpita) where latter was used as benchmark sites. Twelve samples each was collected from the topsoil and the subsoil under each system reaching a total of 96 samples for the four systems. The objective was to assess the potential of the home garden soils to sequester carbon as an alternative to the dwindling carbon storage in forest soils. Analysis of bulk density data of 12 samples each from the HGs and forests showed no significant difference (T-test, α=0.05) between the forests and the HGs for the selected soil depths. Therefore, the assessment of the systems was done in terms of the percentages of soil organic matter (SOM). All the comparisons were done using T test with α=0.05. For the topsoil, Mulatiyana HGs and the forest had mean SOM contents of 4.14%±0.98SD and 5.50%±0.71SD, respectively and, it was significantly different (p=0.001). On the contrary, Wilpita HGs and the forest had values 3.71%±1.6SD and 3.17%±0.059SD, respectively and, they were not significantly different (p=0.296). When the two forests and the home gardens were compared separately, Mulatiyana forest had significantly higher SOM content (p=0.000) over Wilpita forest while the home gardens had no significant difference (p=0.437). When the subsoil was compared neither Mulatiyana forest and the HGs (3.62%±0.64SD, 3.18%±0.70SD; p=0.072) nor Wilpita forest and the HGs (2.60%±1.01SD, 3.10%±1.14SD; p=0.268) had significant differences in the SOM contents. When the two forests and home gardens were compared separately, Mulatiyana forest had significantly higher SOM compared to Wilpita forest (p=0.008) while HGs had no significant difference (p=0.985). These results indicate that the soils of the home gardens adjoining the forests are capable of storing carbon almost up to the natural storage limit for a given locality. Hence, it can be envisioned that the carefully structured home gardens in view of capturing and storage of carbon could be a good alternative for the dwindling forests in the humid tropical environments. Keywords: Soil carbon, Home gardens, Low country, Wet zone

Assessing the phytoavailability of arsenic and phosphorus to corn plant after the addition of an acrylic copolymer to polluted soils.

Soil pollution by arsenic increases the potential risk of arsenic entrance into the food chain. The usefulness of maleic anhydride- styrene- acrylic acid copolymer on the mobility and phytoavailability of arsenic was evaluated. Treatments were the concentrations of acrylic copolymer (0, 0.05, 0.10, and 0.20% w/w) and the concentrations of soil total arsenic (0, 6, 12, 24, 48, and 96mgkg-1). Sodium arsenate was added in appropriate amounts to subsamples of an uncontaminated soil to give contaminated soils with different levels of arsenic. The contaminated soils were subjected to a greenhouse experiment using corn as the test crop. The results showed that contamination of soil by arsenic increased the concentrations of soil available arsenic, root and aerial parts arsenic. By the use of acrylic copolymer, the concentration of available arsenic in the soil and the accumulation of arsenic in the root and aerial parts of the corn plant decreased but the dry weights of the root and aerial parts increased significantly. When the concentration of soil total arsenic was 96mgkg-1, the application of copolymer at the concentration of 0.20% w/w reduced the concentrations of arsenic in soil, root, and aerial parts by 62.53, 43.65, and 37.00% respectively, indicating that application of acrylic copolymer immobilized arsenic in soils.

Distinguishing between natural and anthropogenic sources for potentially toxic elements in urban soils of Talcahuano, Chile

The objectives of this study were (1) to determine the concentrations and background concentrations of Ba, Co, Cr, Mn, and Ni in the urban soils of Talcahuano (Chile); (2) assess the level of contamination in the urban soils based on different pollution indexes; and (3) to identify natural or anthropogenic sources in order to obtain a spatial distribution of the pollutants. A total of 420 samples were collected from the study area as follows: 140 topsoil samples (TS) (0–10 cm), 140 subsoil samples (SS) (10–20 cm), and 140 deep soil samples (DS) (150 cm). The soils were characterized, and the concentrations of Ba, Co, Cr, Mn, and Ni were analyzed by atomic absorption photospectrometry following aqua regia digestion. Correlations and principal component analysis combined with spatial analysis were implemented in order to distinguish the sources and their classification as geogenic or anthropogenic. Several simple and robust statistical methods were applied to datasets in order to explore their potential in the evaluation of a useful and robust background values. The degree of contamination along with the geoaccumulation index, enrichment factor, and contamination factor were also evaluated. The median concentrations obtained for various elements includes Ba 461 mg kg−1, Co 82.7 mg kg−1, Cr 134 mg kg−1, Mn 311 mg kg−1, and Ni 56.1 mg kg−1. In general, the concentrations of Ba, Co, Cr, Mn, and Ni decrease with depth. Correlations and principal component analysis suggest that Cr, Mn, and Ni are contributed by external sources. The spatial distribution of Cr, Mn, and Ni in TS displays a spatial pattern extending along industrial environments and emission sources. The estimated background values determined with the iterative 2σ-technique includes 536 mg kg−1 for Ba, 95.9 mg kg−1 for Co, 208 mg kg−1 for Cr, 464 mg kg−1 for Mn, and 90.5 mg kg−1 for Ni. The geochemical index, enrichment factor, and the contamination factor register a moderate to considerable contamination in some soil samples.

Heavy metal contamination of soil and tree-ring in urban forest around highway in Shanghai, China

ABSTRACTThe heavy metal (HM) pollution of forest soil has been known as one of the most challenging pollution issues due to their characteristics. In order to know the HM pollution condition in urban forest, identify the possible source of HM, 102 sub-samples of soil in 34 sites and 39 tree rings sub-samples in 7 sites were collected in the outer-ring greenbelt (ORG) in Shanghai, China. Concentrations of Cu, Zn, Pb, and Cd in soil and tree rings were analyzed, and the soil properties pH, total nitrogen, total phosphorous, and organic matter were analyzed too. Geo-accumulation index and potential ecological risk index were used for assessing the contamination level of HMs. Nonparametric tests, one-way analysis of variance, correlation analysis, and principal component analysis were applied. The results showed that: (1) concentrations of Cu, Zn, and Cd in soil were significantly higher than their corresponding background values of Shanghai (BVs); concentrations of Cu, Zn, and Pb in tree rings increased gradually in the past 10 years; (2) Zn and Cd were in unpolluted to moderately polluted level, Cd has moderate degree potential ecological risk; (3) vehicle exhausts and abrasion of vehicle parts of tires and historical agricultural activities were the main sources of HM contamination; (4) Cinnamomum camphora (L.) Presl. has the potential to reconstruct the change of Cu, Zn, and Pb as a bioindicator. In conclusion, Cd should be considered as a priority control component. The relationship between plant and soil should take further focus and more studies of the behavior of HMs in soil and plants are required.

Quantifying Diffuse Contamination: Method and Application to Pb in Soil.

A new method for detecting and quantifying diffuse contamination at the continental to regional scale is based on the analysis of cumulative distribution functions (CDFs). It uses cumulative probability (CP) plots for spatially representative data sets, preferably containing >1000 determinations. Simulations demonstrate how different types of contamination influence elemental CDFs of different sample media. It is found that diffuse contamination is characterized by a distinctive shift of the low-concentration end of the distribution of the studied element in its CP plot. Diffuse contamination can be detected and quantified via either (1) comparing the distribution of the contaminating element to that of an element with a geochemically comparable behavior but no contamination source (e.g., Pb vs Rb), or (2) comparing the top soil distribution of an element to the distribution of the same element in subsoil samples from the same area, taking soil forming processes into consideration. Both procedures are demonstrated for geochemical soil data sets from Europe, Australia, and the U.S.A. Several different data sets from Europe deliver comparable results at different scales. Diffuse Pb contamination in surface soil is estimated to be <0.5 mg/kg for Australia, 1-3 mg/kg for Europe, and 1-2 mg/kg, or at least <5 mg/kg, for the U.S.A. The analysis presented here also allows recognition of local contamination sources and can be used to efficiently monitor diffuse contamination at the continental to regional scale.

Isparta Orman Bölge Müdürlüğü’nün Akdeniz iklimi etkisi altındaki Kızılçam (Pinus brutia Ten.) doğal gençleştirme sahalarında anakaya-toprak özelliklerinin ağaç gelişimine etkisi

This study was performed to determine the effect of soil-bedrock properties on growth of natural regeneration areas of Turkish red pine ( Pinus brutia Ten.), which is distributes in sites with Mediterranean climate in Isparta Regional Directorate of Forestry. For this purpose, the study was conducted at 7 different site conditions within natural regeneration areas. The study was carried out with three replicates in all the areas. In these areas, the soil profiles were examined and soil samples were taken from 0-30 cm in each sample plot. Also, values of coordinates, altitudes, aspects and slopes were measured and recorded at each plot. Breast-height diameter and height of 10x3=30 trees in each sample plot were measured and recorded. Soil texture, reaction (pH), organic carbon, total nitrogen and lime analysis were performed on 21 soil subsamples, which were air-dried in the laboratory. Based on the information obtained, breast-height diameter and height of trees were interpolated according to stem analysis for the age of 10. Obtained results showed that there wasn't a negative or positive relationship between growth and soil properties. Bedrock variation has a significant impact on the growth of trees. This effect, besides the varying the position of the physiological depth of sedimentary layer and the position in rock layers as the conglomerate, was determined, it is linked to increased skeletal density of silica.

Recognition of Hydrocarbon Microseepage Using Microbial and Adsorbed Soil Gas Indicators in the Petroliferous Region of Krishna-Godavari Basin, India

The present study aims at exploring the possible correlation between adsorbed light gaseous hydrocarbon distribution pattern and the hydrocarbon oxidizing microbes present in the sub-soil samples. To establish the role of the latter in identifying the upward migration of hydrocarbons, especially a known petroliferous Krishna-Godavari Basin has been investigated. Soil samples from oil and gas fields of Tatipaka and Pasarlapudi areas of the basin show the presence of bacterial population for methane (3.46 × 10 5 cfu/g), ethane (3.85 × 10 5 cfu/g) and propane (3.04 × 10 5 cfu/g) oxidizing bacteria in soil samples. Gas chromatographic analyses of adsorbed soil gases show the presence of C 1 to C 4 hydrocarbons. The concentration of adsorbed soil gases ranged for methane (C 1 ) = 1 to 115 ppb, ethane (C 2 ) = 1 to 99 ppb, propane (C 3 ) = 1 to 34 ppb, butane (nC 4 ) = 1 to 9 ppb and ΣC 2+ = 1 to 115 ppb. The scatter plots between C 1 and C 4 components depict a linear trend indicating that all gases are from the same source. The total organic carbon (TOC) content of the soil samples ranges from 0.18% to 1.34%. Pearson correlation analysis shows that the concentration of ΣC 2+ does not show any correlation (r = 0.1) with TOC, suggesting that the adsorbed gases are not derivatives of the organic carbon. Moreover, the values for methane δ 13 C 1 varied from -39.9‰ to -19.9‰ (V-PDP) Vienna PeeDee Belemnite indicate thermogenic origin. The integration of geomicrobial prospecting method together with adsorbed soil gas and carbon isotope studies shows a good correlation with the producing oil and gas fields of Krishna-Godavari Basin.

Nickel adsorption and desorption in an acric oxisol as a function of pH, ionic strength and incubation time

ABSTRACT Although nickel (Ni) has both important potential benefits and toxic effects in the environment, its behavior in tropical soils has not been well studied. Nickel adsorption-desorption in topsoil and subsoil samples of an acric Oxisol was studied at three pH values (from 3.0 to 8.0). Adsorption-desorption isotherms were elaborated from experiments with increasing Ni concentration (5 to 100 mg L-1), during 0, 4, and 12 weeks, using CaCl2 0.01 and 0.1 M as electrolytic support in order to also verify the effect of Ni-soil time contact and of ionic strength on the reaction. Experimental results of Ni adsorption fitted Langmuir model, which indicated that maximum Ni adsorption (71,440 mg kg-1) occurred at subsoil, after 12 weeks. Nickel affinity (KL) was also greater at subsoil (1.0 L kg-1). The Ni adsorption in the topsoil samples was higher, due to its lower point of zero salt effect (PZSE) and higher organic matter content. The increase in soil pH resulted in the increase of Ni adsorption. Nickel desorbed less from soil samples incubated for 4 or 12 weeks, suggesting that Ni interactions with colloidal particles increase over time. The amount of Ni desorbed increased with increasing ionic strength in both the topsoil and subsoil soil samples. Finally, adsorption-desorption hysteresis was clearly observed. Soil pH, ionic strength of soil solution and the Ni-soil contact time should be considered as criteria for selecting the areas for disposal of residues containing Ni or to compose remediation strategies for acric soils contaminated with Ni.

Patterns of nitrogen and citric acid induced changes in C-turnover and enzyme activities are different in topsoil and subsoils of a sandy Cambisol

Studies on factors controlling C-stability in subsoils are very scarce. Recent results suggest a lack of labile C substrates and N limitations in subsoils as a reason for suppressed C-turnover. The catalytic activity of soil enzymes plays an important role for the decomposition of organic matter in soils and can be a powerful tool to shed further light on substrate and N-limitation as a hypothesized controlling mechanism for C-stability in subsoils. Therefore, we studied the impacts of 14C-labelled citric acid and of NH4NO3 on changes in soil organic carbon (SOC)-mineralization and enzyme activities of dehydrogenase and 9 extracellular enzymes involved in C-, N-, P- and S-cycle. For this approach, we sampled a sandy Cambisol at three different depths (2–12, 35–65 and 135–165cm) and conducted a laboratory incubation experiment for 63days at 10°C. N-addition reduced SOC-mineralization in the topsoil layer by 43%, while no N-effect was observed in both subsoil layers. In the topsoil samples, dehydrogenase-activity also decreased after the incubation with N additions. Further, the activity of extracellular enzymes involved in P- and N-cycling was differently affected in top- and subsoils, indicating that microorganisms in different soil depths have different demands for N or P after adding inorganic N. Additions of citric acid increased SOC mineralization by about 1.9- and 2.2-fold in the upper (35–65cm) and lower subsoil (135–165cm) samples, but only by about 32% in the topsoil samples (2-12cm). The observed priming effect in the topsoil samples was not accompanied by an increased enzyme activity which indicates “apparent priming”. In contrast, priming effects in both subsoil layers were rated as “real priming” indicated by increased enzyme activities and continuously higher SOC-mineralization rates throughout the incubation compared to the controls.

Relationship between multi-element composition in tea leaves and in provenance soils for geographical traceability

The objective of this study was to select the elements in tea leaves correlated with provenance soils, and further build a robust discriminant model of tea according to the geographical origin. Fresh tea leaves along with corresponding topsoil and subsoil samples were collected from three different tea producing regions in China. The concentrations of 20 elements were determined in tea leaf and soil samples. Analysis of variance, Pearson correlation analysis and linear discriminant analysis were used to analyze the obtained data. The results indicated that elemental fingerprinting profiles were different for tea leaves and provenance soils from different regions. The accumulation of some elements in tea leaves was closely correlated with their concentrations in soils. And this study revealed that Na, Mg, Ca, Ni, Rb, Sr and Pb were good descriptors to build discriminant models related to geology for tracing tea.

SENose: An under U$50 electronic nose for the monitoring of soil gas emissions

Tropical soils are major players on CO2 emissions and C cycling on earth. However, it is in tropical countries where scientists can have the most limited access to analytical tools needed for research on these processes. This paper describes the construction and test of a less than U$ 50 chamber for monitoring of multiple soil gas emissions. The system consisted on an array of three MQ series gas sensors placed into an airtight container, a PIC microcontroller and a custom-built software developed for data capture and visualization running on a laptop. A modified multiplexing of sensors was also incorporated in order to allow the parallel analysis in up to eight samples. The chamber, hereafter called SENose (short for Soil Electric Nose), was tested in two separate experiments. The first study used the three sensor array system in soil samples from Colombia and Ecuador, which were separated into two groups in order to study their gas emission patterns in D(+) glucose induced respiration tests. For a second experiment using a multiplexed sensor array in a different set of Colombian soil samples, gas emission patterns were obtained from autoclaved soil with reduced microbial activity, which were further contaminated with diesel oil as C source.During the first study, in replicated 22h continuous runs SENose clearly showed differences in soil respiration patterns of these soil samples, and a prominent timing differential increase in gas production after spiking D(+) glucose, a proxy for organic C, as a substrate. Results of the second study showed a clearly different pattern of gas emissions in diesel oil contaminated samples, when microbial activity was reduced by soil autoclaving. Moreover, two groups of non-autoclaved soil subsamples differing only in diesel oil addition could also be differentiated with basis on their respiration patterns after some hours of gas tracking. Based on these results we foresee a great potential from the use of this low cost system in fields such as soil microbiology, fertility, biotechnology and environmental sciences, where processes such as microbial activity, plant nutrient availability or soil pollutant turnover are tracked by monitoring their gas emission patterns.

Spatial distribution of potentially harmful elements in urban soils, city of Talcahuano, Chile

The objective of this study is to ascertain the spatial distribution of Cu, Pb and Zn in order to determine the degree of contamination in urban soils from Talcahuano (Chile) and to identify the influence of possible contamination sources. A total of 420 samples were collected from the study area based on the following criteria: 140 topsoil samples (TS) (0–10cm), 140 subsoil samples (SS) (10–20cm) and 140 deep soil samples (DS) (150cm). The soils were characterized for their physical characteristics such as grain size distribution, pH, organic matter content etc. and the concentrations of Cu, Pb and Zn were analyzed by Atomic Absorption Photospectrometry following Aqua Regia digestion. Correlations combined with spatial analysis were implemented in order to distinguish the sources of the trace metals and whether they are geogenic or anthropogenic of origin. Several simple and robust statistical methods were applied to the data sets in order to evaluate useful and robust background values. The degree of contamination along with the geoaccumulation index, enrichment factors and contamination factors were also evaluated. The median concentrations obtained for the studied trace metals includes: Cu 23.1mgkg−1, Pb 10.2mgkg−1 and Zn 56.7mgkg−1. In general, the concentrations of Cu, Pb and Zn decrease with depth however, in certain sites the subsoil samples (SS) levels show higher concentrations than topsoil samples (TS). A possible explanation could be related to the uncontrolled clandestine landfill sites using both construction material debris and/or industrial solid wastes. Correlation analysis suggests that Cu, Pb and Zn are contributed by external sources. The spatial distribution of Cu, Pb and Zn in topsoil samples (TS) displays a spatial pattern extending along major roadway environments and emission sources. Estimated background values determined with the iterative 2σ-technique yields 43.7mgkg−1 for Cu, 17.5mgkg−1 for Pb and 91.7mgkg−1 for Zn respectively. The geochemical index, enrichment factor and the contamination factor all register a moderate to high contamination level in some of the soil samples.

Accumulation of cadmium and uranium in arable soils in Switzerland

Mineral phosphorus (P) fertilizers contain contaminants that are potentially hazardous to humans and the environment. Frequent mineral P fertilizer applications can cause heavy metals to accumulate and reach undesirable concentrations in agricultural soils. There is particular concern about Cadmium (Cd) and Uranium (U) accumulation because these metals are toxic and can endanger soil fertility, leach into groundwater, and be taken up by crops. We determined total Cd and U concentrations in more than 400 topsoil and subsoil samples obtained from 216 agricultural sites across Switzerland. We also investigated temporal changes in Cd and U concentrations since 1985 in soil at six selected Swiss national soil monitoring network sites. The mean U concentrations were 16% higher in arable topsoil than in grassland topsoil. The Cd concentrations in arable and grassland soils did not differ, which we attribute to soil management practices and Cd sources other than mineral P fertilizers masking Cd inputs from mineral P fertilizers. The mean Cd and U concentrations were 58% and 9% higher, respectively, in arable topsoil than in arable subsoil, indicating that significant Cd and U inputs to arable soils occurred in the past. Geochemical mass balances confirmed this, indicating an accumulation of 52% for Cd and 6% for U. Only minor temporal changes were found in the Cd concentrations in topsoil from the six soil-monitoring sites, but U concentrations in topsoil from three sites had significantly increased since 1985. Sewage sludge and atmospheric deposition were previously important sources of Cd to agricultural soils, but today mineral P fertilizers are the dominant sources of Cd and U. Future Cd and U inputs to agricultural soils may be reduced by using optimized management practices, establishing U threshold values for mineral P fertilizers and soils, effectively enforcing threshold values, and developing and using clean recycled P fertilizers.

Effects of municipal waste compost and nitrogen fertilizer on growth and mineral composition of tomato

Since simultaneous use of organic and mineral fertilizers on the basis of their chemical compositions can lead to better plant growth and soil fertility, the roles of municipal waste compost (MWC) and nitrogen (N) fertilizer on growth and mineral composition of tomato and some soil properties were evaluated under greenhouse condition. Treatments involved four MWC rates (0, 1, 2, and 4% on the basis of soil dry weight) and four N levels (0, 50, 100, and 200 mg kg−1 soil). Red cloud variety of tomato was sown in treated soils and 9 weeks later dried plant shoots and soil sub-samples were subjected to analysis. Combined use of MWC and N led to better growth of tomato than sole application of either MWC or N fertilizer. Plant concentration and/or uptake of nitrogen, phosphorus, zinc, copper, iron, and manganese were increased by both MWC and N. The beneficial effect of MWC on nutrients uptake was more pronounced with N addition. Plant and soil concentrations of cadmium and lead were under the detection limit of atomic absorption spectrophotometer. Soluble salts, organic matter, sodium, chloride and DTPA-extractable zinc, copper, iron, and manganese in the soil were effectively increased with addition of MWC. Due to high soil pH and calcium carbonate equivalent (CCE) values of the calcareous soil, MWC heavy metals had no hazardous effect on tomato and even played a nutritional role. The most important problem raised from MWC application was the accumulation of soluble salts in the soil which must be monitored when making repeated application of MWC over an extended period of time.

CHEMICAL AND MINERALOGICAL PROPERTIES OF ULTISOLS OF SASAMBA AREA, EAST KALIMANTAN

Ultisols are a major group of marginal soils extensively found in the upland area of Indonesia. To better understand the potential of the Ultisols developed from claystone and sandstone in the Sasamba Integrated Economical Development Area in East Kalimantan, chemical and mineralogical characteristics of 27 Ultisols pedons consisting of 76 topsoil and 118 subsoil samples were investigated. Besides analysis and interpretation of data, relationships of several soil characteristics were constructed using simple regression. The results indicated that Ultisols showed acid to very acid reaction, had low content of organic matter and low base saturation. Soils generally exhibited net negative charge, and the point of zero charge was reached at pH 3.6. Both potential and available phosphates were low, and there was a trend that amorphous aluminum was responsible for phosphate fixation. The low content of exchangeable potassium in topsoil and subsoil indicated a positive correlation with potential potassium. Clay mineral was composed chiefly of kaolinite, with small amounts of illite, vermiculite, and quartz. The domination of kaolinite and low organic matter content causes the soils to have low cation exchange capacity. Soil management in this area should be focused on building up and maintaining soil fertility, and applying appropriate soil conservation techniques to minimize erosion. To obtain sustained productivity, various soil amendments including the use of farm and/or green manure, liming with agricultural lime, and application of rock phosphate and K fertilizers were highly recommended.

CHEMICAL AND MINERALOGICAL PROPERTIES OF ULTISOLS OF SASAMBA AREA, EAST KALIMANTAN

Ultisols are a major group of marginal soils extensively found in the upland area of Indonesia. To better understand the potential of the Ultisols developed from claystone and sandstone in the Sasamba Integrated Economical Development Area in East Kalimantan, chemical and mineralogical characteristics of 27 Ultisols pedons consisting of 76 topsoil and 118 subsoil samples were investigated. Besides analysis and interpretation of data, relationships of several soil characteristics were constructed using simple regression. The results indicated that Ultisols showed acid to very acid reaction, had low content of organic matter and low base saturation. Soils generally exhibited net negative charge, and the point of zero charge was reached at pH 3.6. Both potential and available phosphates were low, and there was a trend that amorphous aluminum was responsible for phosphate fixation. The low content of exchangeable potassium in topsoil and subsoil indicated a positive correlation with potential potassium. Clay mineral was composed chiefly of kaolinite, with small amounts of illite, vermiculite, and quartz. The domination of kaolinite and low organic matter content causes the soils to have low cation exchange capacity. Soil management in this area should be focused on building up and maintaining soil fertility, and applying appropriate soil conservation techniques to minimize erosion. To obtain sustained productivity, various soil amendments including the use of farm and/or green manure, liming with agricultural lime, and application of rock phosphate and K fertilizers were highly recommended.

Determination of homogeneous zones for liming recommendations of black pepper using geostatistics

ABSTRACT Studies aimed at determining homogeneous zones and the spatial variability of soil characteristics may improve the efficiency of agricultural input applications. The purpose of this study was to determine homogeneous zones for liming applications and to characterize the spatial variability of characteristics related to soil acidity and productivity in an Oxisol cultivated with black pepper (Piper nigrum L.). This study was carried out in São Mateus, state of Espírito Santo, Brazil. The experimental site was 100 x 120 m. A grid with 126 sampling points was established. Three soil sub-samples were collected at each sampling point in the black pepper canopy areas, at a 0-0.20 m depth. Crop productivity was estimated by harvesting the three plants neighboring each sampling point. Descriptive statistics and geostatistical analyses were performed. Homogeneous management zones were defined based on map of liming needs. Mathematical models adjusted to semivariograms indicated that all of the studied variables exhibited spatial dependency. An analysis of the spatial variability together with the definition of homogeneous zones can be used to increase the efficiency of soil liming.

Controlling factors for the stability of subsoil carbon in a Dystric Cambisol

Subsoils store >50 % of the total global soil organic carbon (SOC), and low SOC content and high mean residence times indicate that subsoils have the potential to sequester additional C on the long-term. Nevertheless, the mechanisms controlling the turnover of SOC in subsoils are poorly understood. The aim of this study was to assess the impact of temperature and substrate limitation on subsoil SOC turnover and evaluate the stability of additional C inputs in subsoils.In a 63-day microcosm incubation experiment, CO2 production of undisturbed soil samples from topsoil and two subsoil depth increments was measured at two different temperatures (10°C and 20°C). Additionally, 13C labeled root litter was added to the different samples and measurements of the isotopic signature of the respired CO2 allowed a differentiation between SOC mineralization and root mineralization. The CO2 production per unit soil mass was lower in deep subsoil than in the topsoil, but the CO2 production per unit SOC (specific mineralization) was three times higher in the deepest subsoil than in topsoil. This depth gradient of specific mineralization in undisturbed samples indicates that deep subsoil contained relatively more labile SOC than the topsoil. The temperature sensitivity of SOC mineralization expressed as Q10-q, decreased from around 3 to around 1 with increasing soil depth. In contrast, the mineralization of the added root material was solely determined by the recalcitrance of the added roots as indicated by a similar Q10-q through all three soil depths.Contrary to the SOC mineralization of undisturbed samples, significantly more added root litter was mineralized in the samples from the upper horizons than in the deepest subsoil samples, revealing a non-linear relationship between mineralization of added C and the SOC content. Thus, the distance between substrate units, as indicated by the SOC content, may be key factor for subsoil SOC dynamics. Moreover, root addition caused no positive priming effects in subsoil horizons indicating that enhanced C inputs to the subsoil can increase the SOC content and tap the unused C storage potential of subsoils.

Oxidation mechanisms and chemical bioavailability of chromium in agricultural soil – pH as the master variable

Chromium (Cr) is a heavy metal that exists in soils in two stable oxidation states, +III and +VI. The trivalent species is an essential nutrient, whereas the hexavalent species is highly toxic. This study investigated the environmental impact of CrIII potentially released into soil from wastes and various materials by determining the risk of oxidation of initially soluble inorganic CrIII into hazardous CrVI. The principal aim was to describe the pH-dependent mechanisms that regulate 1) the formation of CrVI from the easily soluble CrIII and 2) the potential bioavailability of CrIII and that of CrVI species produced in the oxidation of CrIII in agricultural soil (fine sand, organic carbon 3.2%). The amount of CrVI formed in oxic soil conditions was regulated by two counteracting reactions: 1) oxidation of CrIII into CrVI by manganese oxide (MnIVO2) and 2) the subsequent reduction of CrVI by organic matter back to CrIII. The effect of pH on this net-oxidation of CrIII and on the chemical availability of both CrIII and CrVI species was investigated in soil samples incubated with or without excessive amounts of synthetic MnO2, over the chemically adjusted pH range of 3.9–6.3 (+22 °C, 47 d). In soil subsamples without added MnO2, the net-oxidation of CrIII into CrVI (1 mM CrCl3 in soil suspensions, 1:10 w/V) was negligible. As for the MnO2-treated soils, at maximum only 4.7% of added CrIII was oxidized – regardless of the high oxidation potential of these subsamples. The lowest production of CrVI was observed under acidic soil conditions at pH ∼4. At low pH, the net-oxidation diminished as result of enhanced reduction of CrVI back to CrIII. At higher pHs, the oxidation was limited by enhanced precipitation (or adsorption) of CrIII, which lowered the overall amount of CrIII susceptible for oxidation. Moreover, the oxidation reactions by MnO2 were inhibited by formation of Cr(OH)3 coverage on its surface. The pH-dependent chemical bioavailability of added CrIII differed from that of the CrVI formed. At elevated pHs the chemical availability of CrIII decreased, whereas that of CrVI produced increased. However, the risk of CrVI formation through oxidation of the easily soluble inorganic CrIII was considered to be low in agricultural soils high in organic matter and low in innate MnO2.

Role of nano-goethite in controlling U(VI) sorption-desorption in subsurface soil

Iron oxide nanoparticles in natural soils and sediments can be nanoporous due to the aggregation of nanoparticles. Nanopores can greatly affect the sorption-desorption as well as reduction-oxidation behavior of U(VI) because of their high internal surface area and nanopore confinement effects. Batch U(VI) sorption-desorption experiments were conducted to understand the role of nano-goethite in controlling U(VI) sorption-desorption behavior in saprolite subsoil from Oak Ridge Field Research Center (ORFRC), Tennessee, a premier field research site for environmental remediation. The subsoil samples from ~6.5–8.5m depth were nearly homogeneous in mineral composition (quartz, illite and smectite) and particle size distribution. The subsoil samples were characterized by a range of dithionite-citrate-bicarbonate (DCB) extractable Fe(III) oxide content (127–404μM/g), BET surface area (25–38m2/g), and nanoporosity (pore size<10nm; 16–30μL/g). Transmission electron microscopy (TEM) imaging and X-ray energy dispersive spectroscopy (EDS) analyses revealed that aggregated goethite nano-crystals were poorly crystalline and nanoporous, and U(VI) sorption was dominantly associated with those nanoporous goethite aggregates rather than clay minerals. U(VI) sorption to the saprolite subsoils at circumneutral pH increased with higher amount of nanoporous goethite in the presence of a range of Ca2+ and HCO3−. Sequential extraction of U(VI) pre-sorbed to saprolite subsoils with NaHCO3 (1, 10, and 100mM) exhibited more resistant U(VI) desorption from soils containing higher amount of nanoporous goethite. This study suggests that nano-crystalline goethite with nanoporous structure may exert a significant role in controlling the mobility and transport of U(VI) in subsurface environment where nanoporous minerals are ubiquitous and abundant.