Dry Wt Soil Research Articles

The assessment of air and soil as contributors of some trace metals to vegetable plants II. Translocation of atmospheric and laboratory-generated cadmium aerosols to and within vegetable plants

Radish, spinach and lettuce were grown in the field on 109Cd-laballed soil. Efficient transfer to the plant was observed with concentration factors [Cd cocn. in plant (dry wt) ÷ Cd concn. in soil (dry wt)] of between 0.30 and 2.00. Soil uptake of Cd accounted for only 69–94% of Cd in the plants, the remainder arising from atmospheric deposition. By fumigating radish, lettuce and carrot with Cd aerosol in a wind tunnel and harvesting and analysis subsequent to further growth, translocation of Cd to non-exposed parts of plants was demonstrated. The percentage of deposited Cd which is translocated in the wind-tunnel-fumigated plants is small (0.6–4%), but is larger in plants grown in the field (28–36%) or in a laboratory growth cabinet (12–35%).

Soil-to-vegetation transfer of natural 127I, and of 129I from global fallout, as revealed by field measurements on permanent pastures

Concentrations of natural 127I and of 129I which has been introduced into the environment as fallout from nuclear weapons testing were determined by neutron activation analysis in pasture vegetation and associated soils. The range of concentrations of 129I ( 127I) in the soils was between 2·0 × 10 −14 g/ g and 1·9 × 10 −13 g/ g (dry wt) (3·0 × 10 −8 g/ g and 2·8 × 10 −6 g/ g (dry wt) and in the pasture samples between 4 sd3 × 10 −16 g/ g and 6·9 × 10 −14 g/ g (wet wt) (4·2 × 10 −9 g/ g and 4·9 × 10 −7 g/ g (wet wt)). The soil-to-plant transfer factors (concentration in vegetation (wet wt)/ concentration in soil (dry wt)) for vegetation of permanent pastures for 129I ( 127I) were between B v = 0·01 and B v = 1·05 and ( B v = 0·006 and B v = 0·27). Geometric means for the transfer factors for 129I ( 127I) for pasture vegetation of B v = 0·086 (0·024) were obtained.

Microbial biomass in relation to C and N mineralization during laboratory incubations

Net carbon and nitrogen mineralization rates were determined for an arable soil during 12 weeks at 37†C using an aerobic incubation-leaching technique. The amounts of mineralized C and N were compared to changes in the contents of C and N in microbial biomass (as determined by the chloroform fumigation incubation method; CFIM) during the incubation and to amounts of organic C and N in the leachates. Microorganisms were also followed by direct counting of bacteria, measurements of total hyphal lengths and fluorescein diacetate (FDA)-active hyphae, and by most probable number determinations of protozoa (naked amoebae and flagellates). Numbers of naked amoebae increased nearly 10-fold initially and then decreased between weeks 6 and 12. Bacterial numbers and FDA-active hyphae decreased during the incubation, and the relative composition changed slightly in favour of bacteria. Total hyphal lengths remained almost constant. A total of 105 μg N g' − soil dry wt and 1179 μg C g − soil dry wt was mineralized during the incubation, while the microbial N pool decreased by 42 γm − soil dry wt and the microbial C pool decreased by 225μ g − soil dry wt. Soluble organic matter in the leachates amounted to 16 and 31% of mineralized C and N, respectively. The possibility of measuring C mineralization with less frequent teachings and determinations of N mineralization offers an easy method for assessing changes in labile soil organic matter over time or for comparisons between soils. Through the use of appropriate C-to-N ratios, the N-content in the labile pool can be calculated.

Microbial Biomass, Activity, and Community Structure in Subsurface Soils

ABSTRACTMicrobial biomass, community structure and activity were determined in the subsurface horizons of four contrasting soil types common to Alabama. Biomass and community structure were determined by analyzing the fatty acids of the extractable phospholipids. Activity was estimated by measuring the rate of enzymatic hydrolysis of fluorescein diacetate (FDA). In all four soils, biomass and activity declined with increasing depth; however, the magnitude and pattern of this decline varied as a function of soil type. Biomass concentrations in the lower Ap horizon ranged from 8.2 to 18.0 nmoles phospholipid/g dry wt soil. In the deepest subsoil horizons, the range was 0.0085 to 0.059 nmoles phospholipid/g dry wt soil. The rate of FDA hydrolysis was highly correlated with biomass (r=0.90). Polyenoic fatty acids, which are present only in cukaryotic microorganisms, were found in all horizons; however, their relative abundance differed as a function of soil type. Stepwise regression analysis revealed that soil characteristics could explain 89 and 82% of the variation in biomass and activity, respectively. The results indicated that the vertical distribution of microorganisms in a soil profile differs greatly as a function of soil type. Hence, soil type may be an important determinant as to whether potential ground‐water pollutants are biodegraded as they pass through the unsaturated zone of a soil profile.

Microbial biomass and activity in an agricultural soil with different organic matter contents

Changes in soil fertility caused by various organic and N-fertilizer amendments were studied in a long-term field trial mostly cropped with cereals. Five treatments were included: (I) fallow, (II) cropping with no C or N addition, (III) cropping with N-fertilization (80 kg ha −1 yr −1), (IV) cropping with straw incorporation (1800kg Cha −1 yr −1) and N-fertilization (80 kg ha −1yr −1), and (V) cropping with addition of farmyard manure (80 kg N + 1800kg Cha −1yr −1). The treatments resulted in soil organic matter contents ranging from 4.3% (I) to 5.8% (V). Microbial biomass and activity were determined by chloroform fumigation, direct counting of fungi (fluorescein diacetate (FDA)-staining and Jones-Mollison agar-film technique) and bacteria (acridine orange staining), most probable number determinations of protozoa, esterase activity (total FDA hydrolysis) and respiration. Both biomass estimates and activity measurements showed a highly significant correlation with soil organic matter. Microbial biomass C ranged from 230 to 600 μg C g −1 dry wt soil, as determined by the fumigation technique, while conversions from direct counts gave a range from 380 to 2260 μg C. Mean hyphal diameters and mean bacterial cell volumes decreased with decreasing soil organic matter content.

Microbial Respiration and Chemical Speciation in Metal‐Amended Soils

AbstractSoil microbial respiration was measured on five soils after treatment with metal salt additions (0.0–50 mmol kg−1 metal to dry wt soil) to evaluate the effect of metal toxicity. After 45 d incubation at 20°C, most lower level metal treatments (0.05 and 0.5 mmol kg−1) had little effect on soil microbial respiration, whereas the higher levels (5 and 50 mmol kg−1) sharply inhibited respiration, suggesting a general threshold for metal toxicity between the 0.5 and 5 mmol kg−1 metal.GEOCHEM, an equilibrium thermodynamic computer model, was used to simulate the chemical speciation of Cu and Cd in two soils. Values for the simulated concentration of the “free” Cd2+ species at which 5–10% inhibition of soil respiration occurred (10 µM) were comparable with those measured in pure bacterial culture fluids. Because of adsorption and complexation by the organic soil, more total Cd was required to achieve an equivalent Cd2+ concentration value in the simulated soil solution. The model of simulated Cd species distribution was supported by the fact that equal Cd amendments to both soils resulted in less growth inhibition in the organic soil. When Cd contamination of the two soils was near the toxic threshold level, relatively small increases in soil acidity could markedly increase Cd2+ concentration in the soil solution.Simulated Cu species distribution for the organic soil correlated with inhibition of respiration. Dissolved Cu was predicted to inhibit microbial respiration when the free ion acidity reached a value of 0.01–0.1 µM in the soil solution.

An improved method for determination of adenosine triphosphate (ATP) in soil

Different methods for extraction of ATP from soil were examined. The methods were compared with respect to the efficiency of extraction of ATP from soil, and the content of ATP in the extracts was measured by the luciferin-luciferase system. The following extraction procedure was found to be the most efficient: Shaking of the soil with sulphuric acid, followed by filtration, cation exchange of the extract on Na + resin, and adjustment to pH 9.8 with ethanolamine. The method is simpler, faster and more convenient for processing large numbers of samples, than the earlier-described acid extraction methods. Furthermore, ATP levels of 5ngATPg −1 dry wt soil can be measured and results can be reproduced within ± 5%. The respiration rates of the soils were also measured, and a high degree of correlation was found between carbon dioxide production and ATP levels determined by extraction with sulphuric acid or dimethylsulfoxid.

Ant (Formica exsectoides) Pedoturbation in a Forest Soil

AbstractTwenty‐five active mounds of the common eastern moundbuilding ant (Formica exsectoides) had an average height of 0.37 m and basal diameter of 1.1 m in a long, narrow neverplowed clearing of 1,040 m2 on the edge of a woodland in southern Wisconsin. The mound volume ranged from 0.01 to 0.6 m3 and averaged 0.13 m3. The ant nests, extending at least 160 cm below the soil surface occupied 1.9% of the area of the surface of a Typic Hapludalf (Gray‐Brown Podzolic), Dubuque silt loam, formed in thin loess over reddish cherty clayey residuum on dolomitic limestone. Mounds were virtually bare and were largely composed of silty clay. Detailed studies were made of a soil profile through a large mound and of an intermound soil profile nearby. Calculations indicated that the ants have moved to the surface the equivalent of 1.25% of a plow layer or 2,500 kg of soil (dry wt) per 1,040 m2 and in the process have reduced the bulk density of the material from 1.5 to 0.8 g/cm3 and increased the contents of available nutrients in the soil. Voids 0.2 to 2.3 cm in diameter, on the average occupied 20% by volume of the mound and about 10% of the buried A horizons. The mound contained about 50% silt, 46% clay, 4% sand; 4% free iron oxides, and 3% organic matter. Corresponding figures for the A2 and IIB23 horizons of the Dubuque are: 78, 18, 4; 2 and 3; 15, 83, 2; 6 and 0.3. Disturbance of soil profiles by this species of ant is restricted to small areas, apparently because colonies are established and mounds developed only in temporary openings in forests.