Ineffectiveness of ethylene as a regulator of soil microbial activity

When soils from arable, grassland and woodland environments were incubated aerobically in the presence of up to 50 parts $\text{C}{}_2\text{H}{}_4\text{10}{}^6$, no significant effect of the gas on respiration could be detected. It was concluded that the emanation of C₂H₄ from anaerobic microsites was not responsible for the general regulation of soil microbial activity.     

Water percolation in a tropical alfisol under conventional plowing and no-till systems of management

Field studies were conducted to investigate percolation and redistribution of water in a gravelly Alfisol under conventional and no-tillage systems. Five cm of water tagged with chloride was applied to the soil surface by sprinkling and flood irrigation. Soil samples for water and chloride determinations were obtained immediately after infiltration and at 5, 24 and 48 h after infiltration initiation.Depending on the mean initial soil moisture content ($\text{θ}{}_{\mathrm{<mtext>i</mtext>}}$) and method of water application, mean infiltration rate ranged from 4.6 to 42.9 cm h^?1 for plowed compared to a range of 15 to 120 cm h^?1 for the no-till treatment. In the conventionally plowed soil at $\text{θ}{}_{\mathrm{<mtext>i</mtext>}}\text{= 0.077}\text{cm}{}^3\text{cm}{}^{\mathrm{?3}}$, water penetrated toa depth of 30 cm immediately after infiltration for both sprinkling and flood application. Within 5 h of infiltration initiation, the profile was wetted to 80 cm depth and most of the applied water was retained in the 0–80 cm layer. Samples obtained at subsequent times did not indicate appreciable additional percolation. At $\text{θ}{}_{\mathrm{<mtext>i</mtext>}}\text{= 0.195}\text{cm}{}^3\text{cm}{}^{\mathrm{?3}}$, however, water penetrated to 80 cm depth immediately after infiltration and about 57% of the applied water was retained for sprinkling as well as flood application. At 24 h, retentions were reduced to 17 and 25% for sprinkling and flood application, respectively. Similar results were obtained in no-till fallow or no-till soil cultivated to maize. Percolation in soil under both systems was rapid during the first 5 h after infiltration initiation but decreased rapidly afterwards. After 24 h, however, soil under no-till had more mean water content over the 0–80 cm depth than conventionally plowed treatment.Chloride profile indicated that a large percentage of the added water percolated beyond 80 cm depth without displacing the initially present water. More chloride recovery than water in profiles at high θ_i also indicated some adsorption of chloride in these soils. Adsorption seemed more in the no-till system than in tilled soil.     

Chemical equilibria and quantity—Intensity relationship of zinc in some acid soils of India

Laboratory studies were conducted to investigate the nature of chemical equilibria of zinc in some acid soils of Himachal Pradesh (India). The results indicated that one of the chemical reactions controlling zinc ion activity in the ambient soil solution may be represented by the equation:

$\text{Si(OH)}{}_4\text{+ 2H}{}_2\text{O ? Zn(OH)}{}_2\text{(}\text{crys.}\text{) + SiO}{}_2\text{(}\text{amorph.}\text{) + 2H}{}_3\text{O}{}^{\mathrm{+}}$

Sequential extraction of ⁶⁵Zn-equilibrated soils provided a measure of the intensity of its different forms and their relative contribution to the pool of potentially available zinc in such soils. Adsorption-desorption parameters have been derived from a quattitative treatment of these phenomena as defined by the Langmuir equation. A supply parameter, $\text{√}\text{cq}\text{√K}{}_1\text{K}{}_2$, integrating the combined effects of quantity, intensity and buffering capacity has been derived from the adsorption studies. A linear relationship between the supply parameter and cumulative desorption of applied zind in these soils has been noted. The desorption of zinc from these soils is an exponential process. The solubility relationship of zinc is expressed in terms of the theory of simultaneous equilibria of competitive chemical reactions which obviates the necessity of assuming a single physico-chemical model in predicting and relating the activity of zinc in the ambient soil solution and its surface reactivity on solid phases in the immediate vicinity of plant roots to its ultimate transport and uptake by plants.     

The formation of spherical clay balls on the slopes of sandpit quarry,the Rudice-Seč (Czech Republic)

Clays on the steep slopes of a small artificial sedimentary basin (sandpit quarry) alternately desiccate/crack and erode during hot dry and rainy seasons, respectively. Small irregular blocks of clay (IBC) predefined by cracks are released by gully erosion. The IBCs are quickly transported to the slope base and then rolled down the basin bottom by runoff. Due to rotation about a randomly changing axis and under an effect of deformation forces, the IBCs are transformed into spherical clay balls (SCB). The SCBs are transported, in general, towards the depositional base where they are buried by assorted sandy/clayey sediment. As soon as the kinetic energy of the runoff has decreased, the SCBs remain spread along transport path. From their distribution, the shaping process was evaluated. Based on data processing, the dependency,relating the clay ball projection sphericity, ψ, to the effective diameter, d_ef, and to the distance from the steep slope base, λ, was found. Based on this equation, the length of clay ball transport can be estimated if the projection sphericity and effective diameter are known.     

Effects of nitrite toxicity on soil bacteria under aerobic and anaerobic conditions

Isolates of a soil Pseudoimonas, as well as other soil bacteria, showed a different sensitivity towards NO^?₂ when grown under aerobic or anaerobic conditions. The tolerance to NO^?₂ was increased in the presence of O₂: for instance, a concentration of $\text{200parts}\text{10}{}^6$ of NO^?₂-N proved to be toxic to a Pseudomonas sp. under anaerobic conditions, whereas over $\text{400 parts}\text{10}{}^6$ were needed aerobically to suppress its growth completely. The addition of NO^?₃ as an electron acceptor for anaerobic respiration did not overcome the inhibitive effect of NO^?₃. The pH range, at which NO^?₂ was utilized anaerobically, was narrowed with increasing NO^?₂ concentration (pH 6.8–8.8 at $\text{70 parts}\text{10}{}^6$ of NO^?₂-N and 7.4–8.5 and $\text{140 parts}\text{10}{}^6$ of NO^?₂-N).Tolerance to nitrite varied considerably among the bacteria tested. Each species was able to overcome the inhibitory effect of NO^?₂ up to a certain concentration, while the length of the lag phase was related to NO^?₂ concentration.     

Use of p-benzoquinone and hydroquinone for retardation of urea hydrolysis in soils

Studies to evaluate p-benzoquinone (PBQ) and hydroquinone (HQ) for retardation of urea hydrolysis in soils showed that the effects of these compounds increase markedly with the amount of PBQ or HQ added and decrease markedly with time and with increase in temperature from 10 to 40°C. They also indicated that PBQ and HQ inhibit soil urease activity by identical mechanisms. The effects of various soil properties on the effectiveness of PBQ and HQ for retardation of urea hydrolysis in soils were investigated by studies with 25 surface soils selected to obtain a wide range in pH, texture and organic-matter content. Simple correlation analyses showed that the inhibitory effects of PBQ or HQ on urea hydrolysis in these soils were correlated very highly significantly with organic C content ($\text{r}\text{= ? 0.76}{}^{71}$), total N content ($\text{r}\text{= ? 0.74}{}^{71}$), urease activity ($\text{r = ? 0.70}{}^{71}$) andcation-exchange capacity ($\text{r}\text{= ? 0.62}{}^{71}$). The effects of these compounds also were highly significantly correlated with sand content ($\text{r}\text{= 0.57}{}^7$) and were significantly correlated with silt content ($\text{r}\text{= ? 0.421}$), clay content ($\text{r}\text{= ? 0.491}$) and surface area ($\text{r}\text{= ? 0.491}$), but were not significantly correlated with pH or CaCO₃ equivalent. Multiple-regression analyses indicated that the effectiveness of PBQ and HQ for retardation of urea hydrolysis in soils tends to increase with decrease in soil organicmatter content.     

The analysis of isotherm data to describe polyfunctional exchangers and soils

The analysis of isotherms of cation ion-exchange adsorption in heterogeneous polyfunctional ion-exchangers and soils containing groups of adsorption centres non-equivalent in their preference for exchanging cations permits calculation on the basis of experimental data of the selectivity coefficients ($\text{K}{}_{\mathrm{<mtext>i</mtext>}}$) and maximum adsorption of cations ($\text{S}{}_{\mathrm{<mtext>i</mtext>}}$) for each individual group of heterogeneous centres and thus provides an expression for the exchange isotherm with stable values of $\text{K}{}_{\mathrm{<mtext>i</mtext>}}$ over a wide range of concentrations. A method based on a step-by-step breakdown of the experimental isotherm of ionexchange adsorption was used to describe Ca²⁺ and Pb²⁺ exchange in samples of a leached chernozemic soil. The data obtained demonstrated existence of two groups of non-equivalent adsorption centres. Theoretical and experimental data were found to be in sufficient agreement.     

Animal habitat isolation by roads and agricultural fields

Natural areas are continuously disappearing. Surviving patches resemble islands in terms of limited area, isolation and distance from each other.Road construction and agricultural activities contribute to habitat isolation. Field studies suggest that roads represent barriers and cut off the gene flow by dividing animal populations into fractions on either side of the road.Several mobility diagrams show significant isolation effects of roads on populations of forest-dwelling mice (Apodemus flavicollis) and carabid beetles.Small habitat islands tend to hold more animal species than expected according to the island biogeographic theory. The $\text{N}{}_{\mathrm{s}}\text{N}{}_{\mathrm{i}}$ ratio is highest in small isolates, indicating continuous movement of individual animals from surrounding agricultural areas resulting in unstable species composition.     

Early stages of soil formation on glacial till mine spoils in a semi-arid climate

Strip-mining and the construction of spoil banks composed of unweathered, clay loam textured, moderately calcareous glacial till has provided a model system for studying soil formation in the semi-arid grasslands of southern Saskatchewan. Revegetation of fresh spoils probably occurred within a year or two and includes many native and introduced grasses and herbs. On spoil banks 28–40 years old soluble salts, particularly sodium salts, had leached to considerable depth. Greater soluble cation contents in the surface horizons, as compared to 2.5–5 or 5–10-cm layers, indicated a cycling of these nutrients by vegetation. Nitrogen has accumulated at a rate of $\text{2.43 ± 0.12}\text{g/m}{}^2\text{/yr}$, organic carbon at a rate of $\text{28.2 ± 4}\text{g/m}{}^2\text{/yr}$, suggesting that organic-matter levels characteristic of regional soils could be accumulated in 250–350 years. Cation-exchange capacities increased with the accumulation of organic matter. The fractional composition and spectral properties of humic acids indicated that the humus of soils 28 years old was similar to that of the normal, regional soils. Carbonate weathering appears to be quite slow in grassland environments.     

Water transmission of unsaturated soil samples in relation to mixed Na(Ca + Mg) solutions

The effects of electrolyte concentration (i.e., EC: 20, 40, 80, 125 and 250 meq. l^?1) and sodium adsorption ratios (i.e., SAR: 0, 20, 30, 40, 80 and $\text{α}\text{mmol}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$$\text{l}{}^{\mathrm{<mtext>?1</mtext><mtext>2</mtext>}}$) on water diffusivity (D (θ)) and unsaturated hydraulic conductivity (κ (θ)) were evaluated for samples of sandy loam and clay loam. Both D(θ) and κ(θ) were found to be highly dependent on soil water content, EC and SAR of the infiltrating solution, and texture of sample. In general, the values of D(θ) and κ(θ) decreased with the decrease of water content and EC and increase of SAR and clay content of the sample. The magnitude of these parameters at various degrees of water saturation suggested that the adverse effects of high SAR's and low electrolyte concentrations on the percentage decrease of κ(θ) could be reduced by maintaining a low water content in the transmission zone during infiltration.     

An empirical model for stomatal resistance of field-grown wheat

From concurrent data of stomatal conductance of sunlit leaves (C_i; mm s^?1), leaf water potential (ψ; m), and net radiation (R_n; W m^?2) we derive the empirical relationship:

$\text{C}{}_{\mathrm{l}}\text{=(0.986+0.025R}{}_{\mathrm{<mtext>n</mtext>}}\text{)}\text{1}\text{1+(}\text{ψ}\text{?230.8}\text{)}{}_{5.51}$

Stomatal conductances calculated using the above equation are compared with an independent data set. Canopy resistance derived from the above equation is used in a plant water balance equation to simulate diurnal evaporation fluxes for three days, and we compare the calculated fluxes with lysimeter observations for well-watered and water-stressed wheat. Canopy temperatures are additionally obtained from an energy balance equation and compared with infrared radiometer observations. Regression analysis of simulated and observed evaporation fluxes yields a correlation coefficient of 0.98 and a standard error of estimate of about 37 W m^?2; while for the canopy temperatures the correlation coefficient is 0.98 and the standard error of estimates 1.04°C. Variation of canopy net photosynthesis with insolation, and leaf area index are also simulated and compared with observations.     

Drag coefficient and turbulence intensity in conifer canopies

The relationship between wind speed and drag coefficient was experimentally investigated in two mixed conifer forests of the Italian Alps. Drag coefficient was calculated from the mean momentum equation while canopy architecture was described using optical measurements of gap fraction. Two different formulations of the momentum equation were tested: the common one, where drag forces are expressed in terms of the squared mean velocity ($\text{u}\text{̄}{}^2$), and an alternative one in which drag forces depend on the averaged product of instantaneous wind intensity and instantaneous longitudinal wind component $\text{|U|u}$. Values of drag coefficients computed according to the first approach, decrease with increasing wind speed in both sites and show different average values between sites (0.15±0.14 and 0.34±0.45). Drag coefficients obtained with the second approach do not show a clear dependence on wind intensity, and the mean drag coefficients of the two sites become more similar (0.09±0.06 and 0.12±0.12). According to these results the scaling based on $\text{|U|u}$ seems more appropriate to characterise the physics of the phenomenon.     

Methyl parathion degradation and metabolism in soil: Influence of high soil-water contents

Mineralization of [¹⁴C]methyl parathion (MP) in Cecil sandy loam was considerably reduced when soil-water content was near saturation. Despite the fact that amounts of MP residue in soil held at 10?0 kPa after 35 days were about the same, larger amounts of metabolites were accumulated and higher amounts of non-extractable ¹⁴C-activity were formed in soil held at ? 2.5 kPa than held at ? 6 kPa. Three principal metabolites, p-nitrophenol (PNP), p-aminophenol (PAP) and a water-soluble polar product ($\text{R}{}_{\mathrm{?}}\text{= 0}$), were detected in soil held at ? 2.5 kPa but only PNP and PAP were detected in soil held at ? 6 kPa. The major metabolite PNP behaved like parent MP, in that it was rapidly mineralized in soil held at ? 6kPa. Much slower mineralization was observed in soil held at ? 2.5kPa.