Soil Physicochemical Conditions Research Articles

Can soil testate amoebae be used for estimating the time since death? A field experiment in a deciduous forest

Estimation of the post-mortem interval (PMI, the time interval between death and recovery of a body) can be crucial in solving criminal cases. Today minimum PMI calculations rely mainly on medical and entomological evidence. However, beyond 4–6 weeks even entomological methods become less accurate. Thus additional tools are needed. Cadaveric fluids released by decomposing cadavers modify the soil environment and thus impact soil organisms, which may thus be used to estimate the PMI. Although the response of bacteria or fungi to the presence of a corpse has been studied, to the best of our knowledge nothing is known about other soil organisms. Testate amoebae, a group of shelled protozoa, are sensitive bioindicators of soil physico-chemical and micro-climatic conditions and are therefore good potential PMI indicators. We investigated the response of testate amoebae to three decomposing pig cadavers, and compared the pattern to two controls each, bare soils and fake cadavers, in a beach-oak forest near Neuchâtel, Switzerland. Forest litter samples collected in the three treatments over 10 months were analysed by microscopy. The pig treatment significantly impacted the testate amoeba community: after 22 and 33 days no living amoeba remained underneath the pig cadavers. Communities subsequently recovered but 10 months after the beginning of the experiment recovery was not complete. The fake cadavers also influenced the testate amoeba communities by altering the soil microclimate during a dry hot period, but less than the cadavers. These results confirm the sensitivity of soil testate amoebae to micro-climatic conditions and show that they respond fast to the presence of cadavers – and that this effect although decreasing over time lasts for months, possibly several years. This study therefore confirms that soil protozoa could potentially be useful as forensic indicators, especially in cases with a longer PMI.

Chemical Fractionation and Mobility of Heavy Metals in Soils in the Vicinity of Asphalt Plants in Delta State, Nigeria

Sequential chemical extractions were performed in order to determine the forms of metal contaminants such as cadmium (Cd), cobalt (Co), copper (Cu), chromium (Cr), iron (Fe), manganese (Mn), lead (Pb), nickel (Ni), and zinc (Zn) in the soils around the asphalt plants in Delta State, Nigeria. The results indicated that the reducible phase (consisting of Fe(III) and Mn(IV) oxides, and hydroxides) is the major host of Cd at the surface horizon, while at the sub-surface horizons, cadmium existed mainly in the residual form. Cobalt was predominant in the residual and Fe-Mn oxides fractions. Copper existed mainly in the residual, Fe-Mn oxides and organic bound fractions. Iron and manganese were predominantly in the residual, Fe-Mn oxides and exchangeable fractions. Higher amounts of Mn were extracted in the hydroxylamine hydrochloride extraction than Fe because of specific reduction of Mn oxide by hydroxylamine and specificity of dissolution with respect to ferric oxides. Fe-Mn oxides and residual fractions formed the major host of Pb in these soil profiles while the residual fraction formed the major host of nickel with significant amounts in the exchangeable fraction. Zinc was found predominantly in the Fe-Mn oxides fraction at the topsoils and the residual fractions at the sub-surface soils with significant amounts of zinc occurring in the organic matter bound fraction. The average mobility index of metals in the topsoils follow the order Ni > Cd > Co > Mn ≈ Zn > Fe > Cu > Pb > Cr. The results of the present study revealed that Fe-Mn oxides formed the major scavenging mechanism for metals in these soils. On average the amounts of these metals in the readily available form never exceeded 23% at all depths and sites, implying that these metals are not readily available at the prevailing soil physicochemical conditions. However, significant amounts of these metals existed in the Fe-Mn oxides fraction and may be available if the pH and redox conditions of the soil change, which could be induced by flooding. The results obtained provided information on the speciation, bioavailibity, and mobility of metals in soils in the vicinity of asphalt plants, which are useful in environmental quality management and environmental forensics.

Effect of fulvic acid on the phosphorus availability in acid soil

The incubation experiment was conducted to evaluate the influence of fulvic acid (FA) on phosphorus (P) movement and transformation in acid soil. FA at the rate of 0, 0.1, 0.2, 0.3 g and in combination with 0.19 g KH2PO4 was sprinkled uniformly on the surface of the filter paper on the soil cylinder for 21 days incubation, respectively. The result showed that the pH of soil treated with FA increased from the original value of 5.83 to the highest value of 6.27 in the surface soil layer after 21 days incubation. Due to the application of FA, exchangeable Al concentration evidently decreased in comparison to the only P treatment, which in turn significantly increased available P concentration. FA also increased the movement length of P that reached 4.5, 5.5 and 6.5 cm depth for treatments reinforced with 0.1, 0.2 and 0.3 g FA per column, respectively. As FA was added into soil, microbial population, organic matter content and cation exchange capacity (CEC) all clearly elevated. It is suggested that P fertilizer and FA are fertilized together may be considered as an optimum choice for the improvement of P availability and soil physicochemical conditions.

Phenological Response of Rice Plants to Different Micronutrients Application under Water Saving Paddy Fields on Calcareous Soil

Due to a reduction of world water resources, rice cultivation has shifted from flooded to aerobic condition. This shift may alter soil physico-chemical conditions and cause reduced availability and uptake of nutrients, especially boron and zinc in calcareous soils, and may ultimately reduce yield. Thus a field experiment in a calcareous soil was conducted in which basal application of boron & zinc alone, or in combination, was undertaken in rice grown aerobically (T1), flooded for the entire growth period (T2) or flooded for two weeks after transplanting, given supplemental irrigation up to panicle initiation and then flooded from panicle initiation to physiological maturity (T3). The study showed that rice crop was significantly reduced growth in term of Leaf Area Index (LAI), Leaf Area Duration (LAD), Crop Growth Rate (CGR), Total Dry Matter accumulation (TDM) and Net Assimilation Rate (NAR) when it was grown in aerobic condition. However, the crop was not affected significantly different from normal flooded rice (T2) when it was grown in modified rice culture (T3). Application of zinc alone or in combination with boron enhanced chlorophyll contents in T2similar to T3 while the crop grown in aerobic condition (T1) had significantly lower chlorophyll content

Bacterial diversity in the rhizosphere of maize and the surrounding carbonate‐rich bulk soil

Maize represents one of the main cultivar for food and energy and crop yields are influenced by soil physicochemical and climatic conditions. To study how maize plants influence soil microbes we have examined microbial communities that colonize maize plants grown in carbonate-rich soil (pH 8.5) using culture-independent, PCR-based methods. We observed a low proportion of unclassified bacteria in this soil whether it was planted or unplanted. Our results indicate that a higher complexity of the bacterial community is present in bulk soil with microbes from nine phyla, while in the rhizosphere microbes from only six phyla were found. The predominant microbes in bulk soil were bacteria of the phyla Acidobacteria, Bacteroidetes and Proteobacteria, while Gammaproteobacteria of the genera Pseudomonas and Lysobacter were the predominant in the rhizosphere. As Gammaproteobacteria respond chemotactically to exudates and are efficient in the utilization of plants exudate products, microbial communities associated to the rhizosphere seem to be plant-driven. It should be noted that Gammaproteobacteria made available inorganic nutrients to the plants favouring plant growth and then the benefit of the interaction is common.

Ecophysiological responses of the salt marsh grass Spartina maritima to salinity

The effects of salinity on growth and productivity of Spartina maritima (Curtis) Fernald were investigated in glasshouse and field experiments in 2008. In the glasshouse study, plants were subjected to 2%, 10%, 20%, 40% and 80% sea water, with tidal simulation, for 10 months. Increase in salinity from 2% to 20% sea water increased biomass accumulation, CO2 exchange, quantum yield of Photosystem II (PSII), electron transport rate (ETR) through PSII, and intrinsic photochemical efficiency of PSII, while further increases in salinity to 80% resulted in significant decreases in these parameters. Concentrations of proline increased significantly with increase in salinity up to 80% sea water. In the field study, soil physicochemical conditions between streamside and inland sites were compared, and the constraints imposed by any differences on plant ecophysiological responses determined. At the inland site, soil water potential (ψ), electrical conductivity of the soil, total cations, and the concentrations of Na+, Ca2 +, Mg2 + and P, were significantly higher than those of the streamside site, while CO2 exchange, quantum yield of PSII, ETR through PSII, and intrinsic photochemical efficiency of PSII were significantly lower. The results suggest that S. maritima grows optimally at a salinity of about 20% sea water, and that higher salinity decreases growth and photosynthetic performance.

Soil physicochemical properties and vegetation pattern in an arid environment affected by a salt diaper

Soil degradation, most notably caused by salinization and water-logging, creates formidable problems in arid and semi-arid environments. Advancing our knowledge of salt-affected soils is a prerequisite for understanding how salinization affects environmental concerns, such as soil erosion, nutrient leaching, and lack of vegetation cover. Therefore this study investigated the impact of salt diapirs on soil physicochemical conditions, as well as explored the relationship between halophytic vegetation and soil factors, and described the composition and distribution of plant species in relationship to soil salinity. The study area was divided into three units based on different geomorphologic conditions, slopes and vegetation type.Changes in salinity, soil properties and vegetation were studied. Results showed that the proportion of clay increased while silt and sand decreased with increasing distance from salt diapirs. The presence and kind of ions in all samples consistently indicated high levels of Na, and moderate levels of Mg, Ca, and K. Based on the soil conditions, plant covers were changed to types with more resistance to salinity and water-logging. Typically, this results in a decrease in soil structure stability through degradation of soil aggregates and a variation in the composition of the vegetation toward undesirable species. Key words: Salt diapirs, salinization, soil physicochemical properties, vegetation pattern, arid environment.

Altered food web structure and C-flux pathways associated with mineralisation of organic amendments to agricultural soil

Application of organic materials to agricultural soils offers the potential to divert these from conventional waste streams and to reduce the use of mineral fertilisers for crop production. In addition to direct impacts of organic materials on soil physico-chemical conditions, such amendments may also affect the structure and functioning of soil food webs and the coupling of plant- and soil biological activity. In this study we investigated the impact of cattle slurry and municipal green compost applications on soil microbial and nematode communities. Specifically, we applied steady-state 13C-labelling to quantify the impacts of the amendments on transfer of plant-derived C through components of the soil food web and to determine the activity of the soil biota in mineralising amendment- and soil organic matter derived-C. Both the slurry and compost amendments significantly promoted barley N-acquisition and growth. The municipal compost amendment, but not slurry application, strongly affected soil microbial community structure and increased nematode abundance, relative to unamended soil. This was associated with increased flux of plant-derived C through bacterial (particularly Gram negative) populations in compost-amended soil and was associated with increased mineralisation of amendment- and soil organic matter-derived substrates. For slurry-amended soils, the amendment did not alter soil community structure and mineralisation of soil C was not coupled to the flux of plant-derived C through below-ground pools. The results are indicative of N-supply to barley in compost-amended soil being dependent on the functioning of the soil food web (including C-flux to it from living roots), whereas N-supply from slurry was independent of this coupling between plant and soil processes. We suggest that plant/food web interactions are important targets for development of effective management strategies for organic waste applications to agricultural soils in the context of optimising the balance between nutrient supply to crops and the susceptibility of nutrients to losses from soil.

Distribution of earthworms and influence of soil properties across a successional sand dune ecosystem in NW England

An investigation of earthworms across a sand dune system in NW England examined species distribution and abundance with respect to soil physico-chemical conditions and management. Replicated 0.1 m 2 quadrats were examined every 50 m along 700 m transects across areas of vegetation succession and samples were then taken every 10 m where earthworms were first encountered. A translocation of Aporrectodea longa assessed the ability of this species to live in soils with a high sand content and laboratory work examined growth, maturation and survival of this species in soils with increasing proportions of sand (0–100%). Nine earthworm species were found on the dunes, but none in yellow dunes where organic matter (OM) content was <1%. Dendrobaena octaedra and Lumbricus rubellus were located 300 m from the strand line in grey dunes with an OM content of 3.9%. Allolobophora chlorotica and Lumbricus castaneus occurred within a wet dune slack at 340 m (OM content 11%). In areas of human disturbance (dune car park), A. longa, Aporrectodea caliginosa and Lumbricus terrestris were present, and in soil below pine trees L. castaneus and L. rubellus were present in litter. Laboratory growth of A. longa demonstrated significant ( p < 0.05) increases in growth (2–2.75 g) with 25 and 50% sand compared with 0, 75 and 100% over 24 weeks and a greater rate of maturation. Initial results show earthworm colonisation to be influenced by dune successional stage. Laboratory findings suggested A. longa could exist in higher sand content areas but experimental design needs development. The translocation was unsuccessful. Future investigations could examine soil properties more closely and undertake monitoring on site throughout the year.

Factors Contributing to Dwarfing in the Mangrove Avicennia marina

In Richards Bay, South Africa, Avicennia marina frequently exhibits a distinct productivity gradient, with tree height decreasing markedly from 6-10 m in the fringe zone to <1.5 m in the dwarf zone which is 120 m inland at a slightly higher elevation. In this investigation, soil physico-chemical conditions between fringe and dwarf A. marina were compared and the constraints imposed by any differences on mangrove ecophysiology and productivity determined. Soil and plant samples were analysed for inorganic ions using spectrophotometry. Gas exchange measurements were taken with an infrared gas analyser and chlorophyll fluorescence with a fluorometer. Xylem psi was determined with a pressure chamber and chlorophyll content with a chlorophyll absorbance meter. In the dwarf site, soil salinity, total cations, electrical conductivity and soil concentrations of Na(+), K(+), Ca(2+), Mg(2+), Zn(2+), Mn(2+) and Cu(2+) were significantly higher than those in the fringe zone. Soil water potential and the concentration of soil P, however, were significantly lower in the dwarf site. In the leaves, Na(+) was the predominant ion and its concentration was 24 % higher in dwarf than fringe mangroves. Leaf concentrations of K(+), Ca(2+), Mg(2+), Mn(2+) and P, however, were significantly lower in dwarf mangroves. Photosynthetic performance, measured by gas exchange and chlorophyll fluorescence, was significantly reduced in the dwarf plants. The results suggest that hydro-edaphic factors contribute to high soil salinities, low water potentials, water stress and ion imbalance within tissues including P deficiency, which in interaction, contribute to dwarfing in Avicennia marina.

Factors Associated with Fusarium Crown and Root Rot of Asparagus Outbreaks in Quebec

ABSTRACT The Fusarium spp. causing Fusarium crown and root rot (FCRR) are ubiquitous and abundant in soils, but in contrast, disease expression is localized and sporadic. Previous studies have related FCRR infection to phenolic acids released by asparagus, to the repression of Mn-reducers in soil, and to various soil physicochemical conditions. Fifty commercial asparagus plantations were surveyed using an exploratory approach in order to pinpoint the ecological conditions associated with FCRR development. Twenty-eight variables were used to describe the soil environments of the asparagus crops as well as the influence of crop management practices used locally. The data set was analyzed both as a whole and parsed by main cultivars (Jersey Giant and Guelph Millenium). Both field conditions and percentage of field area affected by FCRR varied widely between asparagus plantations. Planting depth was positively correlated with percentage of field area affected by FCRR and, hence, deep planting may favor FCRR infection. Plantation age was positively correlated with percentage of field area affected by FCRR, while soil available Mn was inversely correlated. Most importantly, soil Mn availability decreased with increasing plantation age, supporting the hypothesis of an asparagusmediated negative impact on Mn-reducing bacteria and of the involvement of reduced Mn availability in FCRR development. Improving the availability of Mn could provide a solution to the problem of FCRR in asparagus plantations.

Evaluating physicochemical constraints of Calcarosols on wheat yield in the Victorian southern Mallee

Soil salinity, sodicity, and high extractable boron (B) are thought to reduce wheat yields on alkaline soils of south-eastern Australia; however, little quantitative information on yield penalties to edaphic constraints is available. The relationships between wheat yield of a B-tolerant cultivar and soil physicochemical conditions in the Victorian Mallee were explored using ridge regression analysis, using natural variation in the field. Wheat yields in the survey ranged from 1.3 to 6.1 Mg/ha, with low yields attributed to inadequate soil water supply during pre-anthesis growth. Crop sequences, fallow–wheat, and pulse–wheat left greatest soil water prior to sowing of the wheat crop, and lucerne–wheat the least. A descriptive model explained 54% of variation in wheat yield, with rainfall around anthesis, available soil water in the 0.10–0.40 m layer, nitrate in the 0–0.10 m layer at sowing and salinity, and sodicity in the 0.60–1.00 m layers being important factors. Subsoil salinity (ECe) and sodicity (ESP) appear to be effective surrogates for estimating the likelihood of water extraction in the deep subsoil. The analyses suggest that subsoils need to have an ECe &lt;8 dS/m and ESP &lt; 19% for crops to make use of water deep in the profile. Although soluble B ranged from 2 to 52 mg/kg in the 0.60–1.00 m layer of the alkaline soils considered, B appeared to have little correlation with root growth, water extraction, or yield of wheat, which has been attributed to B-tolerance of the cultivar tested and/or the overbearing effect of high Na+ in these soils.

Effects of tree species and soil physico-chemical conditions on the nature of soil organic matter

Forty-one properties of the organic matter in surface soil samples collected under oak (intermediate between Quercus petraea and Q. robur) and yew ( Taxus baccata) growing on soils overlying slate and limestone in N.W. England were studied using analysis of variance. Total C, N, polysaccharides, and lipids, the amount of C extracted, and the amount of humic acid C, fulvic acid C, and of the C in the polyphenol fraction of the fulvic acid were related more to the amount of organic matter in a sample than to its chemical nature. The greater C-to-LOI and C-to-N ratios of the samples collected on slate were consistent with different types of transformation of litter compounds by organisms in the soils. The lipid-to-LOI ratio appeared to be lower in soils with high biological activity. The type of humification on limestone was associated with lower ratios of humic acid carbon-to-fulvic acid carbon and a larger percentage of the carbohydrate fraction in fulvic acid, and a larger proportion of the total C was in polysaccharides. The loss of vanillyl units from plant lignin was greater under yew with no significant effect of geology, while the greatest loss of syringyl units occurred under yew on slate. There were statistically-significant, but numerically small, differences in the compositions of the humic acids, the clearest differences being a greater C-to-N ratio and lower N-to- S ratio on slate. The E 4-to-E 6 ratios were correlated positively with humic acid O and O-to-C ratio, which suggests that the ratio decreases with an increase in the degree of condensation.

Microorganisms and soil physico-chemical conditions in the drilosphere of Lumbricus terrestris

The influence of organic matter input into the soil by Lumbricus terrestris on the spatial distribution of microorganisms and on physico-chemical soil characteristics was examined. An experiment was carried out with L. terrestris in soil cores of about 25 cm depth. Lettuce was supplied to the worms as a food source. In the control soil without earthworms, lettuce was manually mixed with the soil. The numbers of total bacteria, siderophore producing bacteria and fluorescent pseudomonads were greatest in the casts and burrowing walls of the 0–5 cm soil layer (1.5 × 10 9, 1.6 × 10 8 and 4.4 × 10 7 CFU g −1 of dry soil, respectively). Numbers in the uningested soil from the same soil layer were 60–320 times smaller. In the deeper soil layers (5–22 cm), bacterial numbers in the uningested soil were 6–32 times smaller than in the burrow walls. The bacterial counts for the control soil were intermediate between the counts for the casts + burrow walls and the counts for the uningested soil. Over the depth of soil studied, the NO 3 −N content of the casts and burrow walls was 1.2- to 2.1-fold greater than in the uningested soil, but it was only greater than the control soil (notably 1.66-fold) in the top layer (0–5 cm). The distribution of microorganisms and nutrients along the earthworm burrows was associated with good water availability and improved aeration. Based on these observations, the drilosphere of actively feeding L. terrestris is considered to be one of the most important microbial niches in soil.

Effect of CH 4 concentrations and soil conditions on the induction of CH 4 oxidation activity

Four different soils (meadow cambisol, forest luvisol, cultivated cambisol, paddy soil) were incubated under different CH 4 mixing ratios (1.7 μl CH 4 l −1 to 20% CH 4) in air (20% O 2, rest N 2) and the CH 4 oxidation activities as well as the numbers of methanotrophic bacteria were determined. All soils showed an increase of the microbial CH 4 oxidation activity and the numbers of methanotrophic bacteria only if incubated at CH 4 mixing ratios exceeding about 100–1000 μl CH 4 l −1. The induction of the CH 4 oxidation activity was strictly O 2-dependent and was inhibited by acetylene or autoclaving, demonstrating that CH 4 oxidation in the soil was due to methanotrophic bacteria. The induction process was influenced by physico-chemical soil variables such as soil moisture, pH, temperature, NH 4 + concentration, Cu 2+ concentration and aggregate size. Optimum ranges for the induction process were: soil water content of 20–35% H 2O; pH 6.7–8.1; temperatures of 25–35°C; and NH 4 + concentrations in the soil water phase of 12–61 m m. Copper concentrations >4.3 m m Cu 2+ inhibited the induction of CH 4 oxidation activity. Increasing soil aggregate sizes between 50 μm and >2 mm dia resulted in a slight but steady stimulation of the induction. Our results demonstrate that the development of an active methanotrophic population in oxic soils requires not only sufficient CH 4 but also soil physico-chemical conditions that are suitable for growth or activation of methanotrophic bacteria.

PHOSPHORUS RELEASE AND ASSIMILATORY CAPACITY OF TWO LOWER MISSISSIPPI VALLEY FRESHWATER WETLAND SOILS

ABSTRACT: Phosphorus fluxes and water quality functions of a bottomland hardwood and freshwater marsh wetland soil were compared. The effect of soil physicochemical conditions, phosphorus loading rate, and diffusive exchange between soils and the overlying food water column on phosphorus release and retention were studied. The predominantly mineral swamp forest soil displayed greater phosphorus sorption potential than the organic freshwater marsh soil. Moreover, due to its low bulk density (0.11 g cm−3), the freshwater marsh soil surface area required for phosphorus retention is very large compared to the bottomland hardwood wetland soil. For both wetlands, soil redox status affected P release and assimilatory capacity. The more reducing the soils, the smaller their phosphorus retention capacity (greater their release). Phosphorus removal from the overlying water column into the wetland soils followed a first-order kinetic model. Under similar hydrological conditions, phosphorus was found to diffuse 1.2 times faster to the bottom. land hardwood soil than in the freshwater marsh soil. Results indicate that while the bottomland hardwood wetland soil will serve as a sink for phosphorus entering such wetland, phosphorus will be released and exported from the freshwater marsh soil into adjacent ecosystems.

Effect of addition of various carbon substrates on denitrification in a vertic Mollisol

Glucose, acetate, malate, and citrate were added to an agricultural soil. The pe values (-log e-; calculated from the redox potential) obtained 30 min after the addition of C were not correlated with the theoretical reducing power nor with the theoretical total energy of the C compounds. By contrast the number of electron (e-) equivalents was correlated with pe7, indicating that the proton number affected the redox potential (Eh) measurement. After 24 h of incubation, denitrification rates followed the order citrate>malate>glucose and control. No N2O production was detected with acetate. Denitrification was not correlated with the theoretical reducing power of the added C compounds but was correlated with pe+pH. Similar numbers of e- equivalents were measured with all treatments. After 72 h of incubation, the order of the denitrification rates was malate>citrate >acetate>glucose and control. The Eh values (lower than after 24h) did not differ with treatment while the number of e- equivalents was influenced by the quality of the C source. This also demonstrates that the proton number affected the measured Eh. Our results suggest that the different C substrates did not directly influence the soil physicochemical and biological conditions through their degree of oxidation. Any effects appeared to be indirect, arising from the ability of the substrates to generate new metabolites, and consequently initiate different metabolic pathways that modified the soil physicochemical conditions, reducing power and microbial activity.