When soils from arable, grassland and woodland environments were incubated aerobically in the presence of up to 50 parts , 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. 相似文献
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 () 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 , 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 , 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 θi also indicated some adsorption of chloride in these soils. Adsorption seemed more in the no-till system than in tilled soil. 相似文献
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 ) 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. 相似文献
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 (), total N content (), urease activity () andcation-exchange capacity (). The effects of these compounds also were highly significantly correlated with sand content () and were significantly correlated with silt content (), clay content () and surface area (), 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. 相似文献
Dentrification rates in two soils were assessed separately as a function of NO3? concentration while providing a constant initial glucose concentration, and as a function of glucose concentration while providing a constant initial NO3?-N concentration. Of the soils used, a Hanford sandy loam and a Coachella fine sand, the bacteria in the former produced higher rates of denitrification with a maximum loss of 1500 μg NO3?-N/ml day?1 as compared to a loss of 150 μg NO3?-N/ml day?1 from the latter. Rates of loss closely approximated Michaelis Menten kinetics in the Coachella sand, and Km values for glucose-C and NO3?-N were 500 μg/ml and 170 μg/ml, respectively. Rates of loss of NO3?-N from the Hanford soil did not approximate Michaelis-Menten kinetics, and this was attributed to failure to saturate enzyme systems in the denitrifying bacteria with glucose and nitrogen when each was held constant. C/N ratios around 2 appeared to provide the greatest rates of denitrification. High C/N ratios or high glucose concentrations (1.8 per cent) retarded denitrification, with fungal growth and a subsequent drop in pH occuring. A Pseudomonas was incubated aerobically for 24 h followed by a 72 h anaerobic incubation with nitrate as the sole nitrogen source at 0, 10, 50, 100, 250 and 500mg N/ml concentrations. Assimilatory nitrate reduction never exceeded 75 mg N/ml, and it was concluded that this mode of nitrate reduction is insignificant at higher nitrate concentrations by comparison to dissimilatory nitrate reduction, i.e. denitrification. 相似文献
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, def, 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. 相似文献
From concurrent data of stomatal conductance of sunlit leaves (Ci; mm s?1), leaf water potential (ψ; m), and net radiation (Rn; W m?2) we derive the empirical relationship: 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. 相似文献
Soil microorganisms, inducing bacteria, fungi imperfecti, and basidiomycetes were investigated to determine their roles in lignin degradation. White-rot basidiomycete fungi and some bacteria demonstrated ability to degrade specifically-labeled synthetic lignins (DHPs). White-rot basidiomycetes degraded methoxyl groups and bacteria degraded side chains most rapidly. Fungi imperfecti, brown-rot basidiomycetes and some bacteria were unable to degrade DHPs. Interactions of white-rot basidiomycetes with imperfects usually resulted in decresed rates of DHP degradation. Attempts to correlate the ability to degrade DHPs with ability of the microorganisms to grow upon aromatic C sources, demethylate and produce monooxygenases, dioxygenases, and polyphenoloxidases were unsuccessful. 相似文献
Effects of addition of increasing amounts of fulvic acid (FA) on the crystallization of aluminum hydroxides from AlCl3, solution, neutralized to different degrees, were investigated. All systems were allowed to age at 30°C for 70 days.In the absence of FA, gibbsite was formed at pH 6, a mixture of nordstrandite and bayerite at pH 8, and bayerite crystallized at pH 10. At pH 6 and 8, the addition of increasing amounts of FA (up to 10 mg/l or ) first delayed and then inhibited the crystallization of these aluminum-hydroxide polymorphs but tended to favor the crystallization of pseudoboehmite, an aluminum oxyhydroxide. At pH 10, the addition of FA totally inhibited crystallization and precipitation.Our data suggest that FA so strongly complexes Al that it prevents its full hydroxylation to Al(OH)3. Another explanation is that the action of FA on the crystallization of aluminum hydroxides resembles that of salts in that FA appears to favor the formation of Al-O-Al (oxo) over that of (ol) linkages. Either reaction mechanism throws new light on the genesis of some bauxites, which consist of submicroscopic boehmite-like particles which are very similar to pseudoboehmite. 相似文献
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 (), 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. 相似文献
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 , organic carbon at a rate of , 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. 相似文献
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: 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, , 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. 相似文献
Extraction of soil nitrate nitrogen (NO3?-N) and ammonium nitrogen (NH4+-N) by chemical reagents and their determinations by continuous flow analysis were used to ascertain factors affecting analysis of soil mineral N. In this study, six factors affecting extraction of soil NO3?-N and NH4+-N were investigated in 10 soils sampled from five arable fields in autumn and spring in northwestern China, with three replications for each soil sample. The six factors were air drying, sieve size (1, 3, and 5 mm), extracting solution [0.01 mol L?1 calcium chloride (CaCl2), 1 mol L?1 potassium chloride (KCl), and 0.5 mol L?1 potassium sulfate (K2SO4)] and concentration (0.5, 1, and 2 mol L?1 KCl), solution-to-soil ratio (5:1, 10:1, and 20:1), shaking time (30, 60, and 120 min), storage time (2, 4, and 6 weeks), and storage temperature (?18 oC, 4 oC, and 25 oC) of extracted solution. The recovery of soil NO3?-N and NH4+-N was also measured to compare the differences of three extracting reagents (CaCl2, KCl, and K2SO4) for NO3?-N and NH4+-N extraction. Air drying decreased NO3?-N but increased NH4+-N concentration in soil. Soil passed through a 3-mm sieve and shaken for 60 min yielded greater NO3?-N and NH4+-N concentrations compared to other treatments. The concentrations of extracted NO3?-N and NH4+-N in soil were significantly (P < 0.05) affected by extracting reagents. KCl was found to be most suitable for NO3?-N and NH4+-N extraction, as it had better recovery for soil mineral N extraction, which averaged 113.3% for NO3?-N and 94.9% for NH4+-N. K2SO4 was not found suitable for NO3?-N extraction in soil, with an average recovery as high as 137.0%, and the average recovery of CaCl2 was only 57.3% for NH4+-N. For KCl, the concentration of extracting solution played an important role, and 0.5 mol L?1 KCl could fully extract NO3?-N. A ratio of 10:1 of solution to soil was adequate for NO3?-N extraction, whereas the NH4+-N concentration was almost doubled when the solution-to-soil ratio was increased from 5:1 to 20:1. Storage of extracted solution at ?18 °C, 4 °C, and 25 °C had no significant effect (P < 0.05) on NO3?-N concentration, whereas the NH4+-N concentration varied greatly with storage temperature. Storing the extracted solution at ?18 oC obtained significantly (P < 0.05) similar results with that determined immediately for both NO3?-N and NH4+-N concentrations. Compared with the immediate extraction, the averaged NO3?-N concentration significantly (P < 0.05) increased after storing 2, 4, and 6 weeks, respectively, whereas NH4+-N varied in the two seasons. In conclusion, using fresh soil passed through a 3-mm sieve and extracted by 0.5 mol L?1 KCl at a solution-to-soil ratio of 10:1 was suitable for extracting NO3?-N, whereas the concentration of extracted NH4+-N varied with KCl concentration and increased with increasing solution-to-soil ratio. The findings also suggest that shaking for 60 min and immediate determination or storage of soil extract at ?18 oC could improve the reliability of NO3?-N and NH4+-N results. 相似文献
With the organic carbon of acetate (SBR-A) and propionate (SBR-P), the effect of organic carbon sources on nitrogen removal and nitrous oxide (N2O) emission in the multiple anoxic and aerobic process was investigated. The nitrogen removal percentages in SBR-A and SBR-P reactor were both 72%, and the phosphate removal percentages were 97 and 85.4%, respectively. During nitrification, both the NH4+-N oxidation rate in the SBR-A and SBR-P had a small change without the influence of the addition of nitrite nitrogen (NO2?-N). With the addition of 10 mg/L NO2?-N, the nitrate nitrogen (NO3?-N) production rate, N2O accumulation rate and emission factor had increased. At the same time, the N2O emission factor of SBR-A and SBR-P reactors increased from 2.13 and 0.87% to 4.66 and 2.08%, respectively. During exogenous denitrification, when nitrite was used as electron acceptor, the N2O emission factors were 34.1 and 8.6 times more than those of NO3?-N as electron acceptor in SBR-A and SBR-P. During endogenous denitrification with NO2?-N as electron acceptor, the accumulation rate and emission factor of N2O were higher than those of NO3?-N as electron acceptor. High-throughput sequencing test showed that the dominant bacteria were Proteobacteria and Bacteroidetes in both reactors at the phylum level, while the main denitrification functional bacteria were Thauera sp., Zoogloea sp. and Dechloromonas sp. at the genus level. 相似文献
The possible formation of carcinogenic nitrosamines in soils was examined. Soil samples amended with NO2?-N and dimethylamine incubated for 30 days and analysed every 3 days, showed increasing amounts of dimethylnitrosamine up to 12–15 days. The concentration reached as high as 6.5 parts/106, thereafter, a decline was noted. Most of the nitrosamines disappeared in soils after 30 days. Addition of inorganic N reduced the decomposition of dimethylamine. Soil incubation studies with NO2? and trimethylamine showed about 80% reduction in the amount of nitrosamines formed as compared to dimethylamine. Analysis of soil samples from fertilized and polluted areas showed significant amounts of NO?3-N but no nitrosamines. Application of 10 parts/106 of dimethylamine to these soil samples resulted in the formation of 0.10 to 0.50 parts/106 of nitrosamines. Autoclaved soil samples incubated with NO2? and dimethylamine for 12–15 days produced small amounts of nitrosamines. Addition of glucose to soil samples increased the amounts of nitrosamines formed. 相似文献
