The effects of cropping corn on the extractability of zinc added to a calcareous soil

The effects of cropping corn on the decrease in the extractability of Zn added to a calcareous soil were studied by a pot experiment and chemical extractions. The results show that the concentrations of Zn exchangeable with MgCl₂ (EXC-Zn) and extractable with DTPA (DTPA-Zn) in the soils with added Zn decreased with time. The processes associated with the decrease in extractability in DTPA of Zn added to soil can be described aptly by a diffusion equation which gives the proportion of added Zn in the non-DTPA fraction as a function of the square root of incubation time. This result suggests that the diffusion of Zn cations into microporous solids is a rate-limiting reaction. The relative diffusion rate coefficients (D/r²) were found to be 1.95×10^-10 and 3.34×10^-10 sec^-1 in the soils with added Zn of 20 and 60 mg kg^-1, respectively. Compared with uncropped soil, the concentrations of DTPA-Zn in the soils with added Zn were decreased by cropping. The decrease of DTPA-Zn in the soils in the presence of corn can be attributed to both its acquisition by corn and other processes associated with the growing of corn. The activity of plant roots would appear to enhance the process of decrease in the extractability in DTPA of Zn added to the soil. The source of Zn uptake by corn was affected by the loading or activity of Zn in soil. In the soil with low available Zn, the DTPA non-extractable Zn (non-DTPA-Zn) was mobilized and taken up by corn. In the soils with high available Zn, e.g. the recently added Zn, only EXC-Zn and a part of the DTPA-Zn were taken up by corn.     

Evaluation of three herbaceous index plant species for bioavailability of soil cadmium, chromium, nickel and vanadium

Uncultivated plants growing on disturbed sites may be useful for assessing the bioavailability of some metals in soils, and thus the potential for metal mobilization up the terrestrial food chain, an important element in ecological risk assessment. A planted chicory cultivar (Cichorium intybus L. var. foliosum Hegi.) and the uncultivated plants horseweed (Canada fleabane) (Erigeron canadensis L.) and dogfennel (Eupatorium capillifolium (Lam.) Small) were evaluated for their ability to act as index plant species for soil Cd, Cr, Ni, and V at two field sites where these metals had been applied five yr previously to two highly weathered sandy Ultisols. Soil Cd was available to all analyzed plant tissues of all three plant species at both sites, particularly on the sandier Blanton soil. Chicory was an effective index plant for Cd on the finer textured Orangeburg soil but functioned as an indicator plant (toxicity symptoms were observed) on the sandier Blanton soil. Horseweed and dogfennel were effective index plants for Cd in both contaminated soils. Soil Cr, Ni, and V were less bioavailable than soil Cd and plant metal uptake was more sensitive to residual soil Cr, Ni, and V than was soil extraction with double acid. Horseweed and chicory may have potential as index plants for soil Cr. Chicory may have potential as a Ni index plant. Chicory and dogfennel may have potential as V index plants.     

Chemical soil conditions in pristineNothofagus forests of New Zealand as compared to German forests

In many German forest soils low base saturation of CEC in deeper soil layers was reported and acidic deposition is seen as the major cause of these findings. To test this hypothesis we sampled 5 New Zealand forest soils from pristine beech (Nothofagus fusca, N. menziesii, N. solandri) sites under climatic and geological conditions comparable to higher elevations in Germany. The soils developed from granite and greywacke. Soil samples were analyzed for pH and the exchangeable cations were extracted with 1M NH₄Cl. The base saturation of all soil profiles was very low, even in deeper layers and was thus similar to the patterns found in many German forest soils. The pH was generally higher in the New Zealand soils as compared to Germany. The reason for the depletion of base cations in deeper soil layers of New Zealand forest soils is most likely the leaching of base cations with HCO₃ ^- resulting from the dissociation of carbonic acid in connection with high amounts of seepage. Thus, under high rainfall conditions, the low base saturation found in deeper layers of forest soils cannot exclusively be attributed to the effects of acidic depositions and land use. ei]Section editor: R F Huettl     

The effects of soil warming on plant recruitment

We demonstrate, using a simple field experiment, that soil warming is sufficient, independent of other cues, to potentially alter the recruitment of Betula pendula seedlings. This study suggests that changing temperature, and correlated changes in edaphic factors, can alter patterns in plant recruitment via differential effects on seed dormancy. Increased soil temperatures (of less than 5 °C) throughout the year led to a significant increase in the number of birch seedlings that emerged from soil samples collected in the spring. No concomitant changes in the emergence of other species was observed. Such temperature induced changes in seedbank dynamics and their subsequent effects on the competitive interactions within a plant community suggest far reaching ecological consequences of current increases in global temperature.     

Predicting badger sett numbers: evaluating methods in East Sussex

Abstract. One way in which a species' numbers may be estimated without direct counting is to predict their dispersion and density from more readily available habitat measures, such as landscape variables measured from maps or vegetation variables measured in the field. We compare the power of ordination and regression techniques for predicting badger ( Meles meles L.) numbers at a local scale, using a land class system, map-read landscape variables and field-derived vegetation variables. Sett density was used as a surrogate of badger density. Multiple linear regression using vegetation and landscape variables together gave the most accurate prediction of sett density, while ordination techniques were of lesser value. The addition of vegetation variables to landscape variables did not substantially improve the power of ordination. Outlier Sett Density was predicted more accurately, and by different variables, to Main Sett Density. The relationship between badger ecology and habitat variables that were useful in predicting sett density is discussed.     

Observations on the maintenance and measurement of soil water in simple pot experiments and its effects on seed-borne Fusarium culmorum seedling blight of winter wheat

A simple method for maintaining and measuring soil water and the relationship between soil water and seed-borne Fusarium culmorum seedling blight of wheat was investigated under controlled environmental conditions to develop reproducible assay conditions for epidemiological studies and the testing of fungicide seed treatments. For reproducibility, soil matric potential (ψ_m) was used to define soil water, and a range of watering regimes were tested. Treatments were watered to either a maximum ψ_m or to maintain a mean ψ_m in order to establish which parameter best described the effect that soil water had on the incidence of disease symptoms. The severity of disease symptoms was closely related to the mean soil water status and not the maximum ψ_m value. Watering intervals, ranging from three times a day to once every three days, did not affect this relationship. The percentage of seedlings showing symptoms after emergence (i.e. localised or extensive necrotic lesions) was inversely related to the mean ψ_m. With increasing soil dryness (mean ψ_m from -0.14 MPa to -0.17 MPa) the percentage of seedlings with post-emergence symptoms decreased from 50% to 20%. However, as the mean ψ_m changed from -0.14 MPa to -0.17 MPa the percentage of seedlings dying before emergence increased from 25% to 55% in direct proportion to ψ_m. Overall the incidence of infection as indicated by the total number of seedlings showing symptoms either before or after emergence remained relatively constant, and was not significantly related to mean ψ_m.     

Control of Chenopodium album by soil application of Ascochyta caulina under greenhouse conditions

Effects of soil application of Ascochyta caulina spores on seedlings of Chenopodium album and five cultivated plant species were investigated under greenhouse conditions as a part of a study on biological control of C. album. Application of A. caulina spores to soils resulted in disease development on C. album and to a lesser degree on Spinacia oleracea seedlings, but not on Beta vulgaris subspecies vulgaris, Zea mays, Triticum aestivum and Pisum sativum seedlings. Affected C. album seedlings had an abnormal olive-green colour or necrotic spots on cotyledons and hypocotyls, and were stunted or died. Affected S. oleracea seedlings were pale in colour or had necrotic spots on the cotyledons, but did not die. Time courses of disease incidence and of mortality of C. album could be described by a monomolecular model. Effects of spore density, sowing depth, soil water content, soil type and time of sowing on disease development were examined. Disease incidence and mortality were influenced by spore density, soil water content and soil type, but not by sowing depth. Spores in a moist soil maintained infectivity at least 2 wk. Spore densities of 10⁹ to 10¹⁰ spores m^-2 were required for 50% mortality of emerged C. album plants. Aspects of the development of A. caulina into a soil-applied mycoherbicide are discussed.     

Effect of concentration and environmental form of tetradecenyl succinic acid on its mineralization in soil

Tetradecenyl succinic acid (TSA) is the major component of a detergent builder (C12-C14 alkenyl succinic acid), which is inherently biodegradable. ¹⁴C-TSA was dosed as a component of sewage sludge into a soil with a history of sludge amendment at final added concentrations of 1.5 and 30 mg (kg soil)^-1. In addition, it was dosed to the soil in an aqueous solution to a final added concentration of 30 mg (kg soil)^-1. Dose and form were found to have a pronouced effect on the mineralization kinetics. When dosed in a realistic form and concentration (i.e. 1.5 mg (kg soil)^-1 as a component of sludge), TSA was mineralized at its highest rate and to its greatest extent, and the mineralization half-life was 2.4 days. When dosed at 30 mg (kg soil)^-1 as a component of sludge, mineralization began immediately, and the half-life was 23 days. In contrast, when dosed at this concentration in aqueous solution, the onset of mineralization was preceded by a 13 day lag period and the mineralization half-life was 69 days. Primary biodegradation and mineralization rates of TSA were very similar. Approximately, half the radioactivity was evolved as ¹⁴CO₂, while the remaining radioactivity became non-extractable, having presumably been incorporated into biomass or natural soil organic matter (humics). This study demonstrated that TSA is effectively removed from sludge-amended soils as a result of biodegradation. Furthermore, it showed the effect that dose form and concentration have on the biodegradation kinetics and the importance of dosing a chemical not only at a relevant concentration but also in the environmental form in which it enters the soil environment.     

Past vegetation changes in the Brazilian Pantanal arboreal–grassy savanna ecotone by using carbon isotopes in the soil organic matter

Measurements of the organic carbon inventory, its stable isotopic composition and radiocarbon content were used to deduce vegetation history from two soil profiles in arboreal and grassy savanna ecotones in the Brazilian Pantanal. The Pantanal is a large floodplain area with grass-dominated lowlands subject to seasonal flooding, and arboreal savanna uplands which are only rarely flooded. Organic carbon inventories were lower in the grassy savanna site than in the upland arboreal savanna site, with carbon decreasing exponentially with depth from the surface in both profiles. Changes in ¹³C of soil organic matter (SOM) with depth differed markedly between the two sites. Differences in surface SOM ¹³C values reflect the change from C₃ to C₄ plants between the sites, as confirmed by measurements of ¹³C of vegetation and the soil surface along a transect between the upland closed-canopy forest and lowland grassy savanna. Changes of ¹³C in SOM with depth at both sites are larger than the 3–4 per mil increases expected from fractionation associated with organic matter decomposition. We interpret these as recording past changes in the relative abundance of C₃ and C₄ plants at these sites. Mass balances with ¹⁴C and ¹³C suggest that past vegetational changes from C₃ to C₄ plants in the grassy savanna, and in the deeper part of the arboreal savanna, occurred between 4600 and 11 400 BP, when major climatic changes were also observed in several places of the South American Continent. The change from C₄ to C₃, observed only in the upper part of the arboreal savanna, was much more recent (1400 BP), and was probably caused by a local change in the flooding regime.