摘要:

SUMMARYThe isotope dilution method for measuring gross rates of N mineralization, immobilization, and nitrification was applied to intact soil cores so that the effects of soil mixing were avoided. Soil cores were injected with solutions of either15NH4+or15NO4−; gross mineralization rates were calculated from the decline in “N enrichment of the NH: pool during a 24‐h incubation; gross nitrification rates were calculated from the decline in15N enrichment of the NO−3pool; gross rates of NH4+and NO3−consumption were calculated from disappearance of the15N label. The assumptions required for application of this method to intact cores are evaluated. Sensitivity analysis revealed that homogeneous mixing of added “N with ambient pools was not a necessary assumption but that bias in distribution of added label, coincident with a non‐random distribution of microbial processes, would cause significant errors in rate estimates. Rate estimates were also sensitive to errors in initial15N and14N pool size estimates, In a silt loam soil from a grassland site, abiotic processes consumed over 30% of the added15NH4+within minutes of adding the label to sterilized soil. Extracting a subset of soil cores at the beginning of an incubation is recommended for obtaining initial pool size estimates. Gross immobilization is probably stimulated by addition of inorganic15N substrate and, therefore, is overestimated by the isotope dilution method. As an alternative method, a non‐linear equation is given for calculating the gross immobilization rate from the appearance of15N in chloroform‐labile microbial biomass; but incomplete extraction of biomass N may result in low estimates. Details of the isotope dilution methodology (injection rates, concentrations, experimental artefacts, etc.) are described and discussed. When care is taken to understand the underlying assumptions and sources of error, the isotope dilution method provides a powerful tool for measuring gross rates of microbial transformations of soil nitrogen in

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1991.tb00413.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

SUMMARYNitrous oxide (N2O) emissions and concentrations in the soil atmosphere were measured at a number of sites of differing soil type in south‐east Scotland between 1985 and 1988. Concentrations followed log‐normal distributions and were significantly affected by soil type, tillage treatment, and nitrate application rate. The shape of the profiles suggested significant consumption in the upper 5 cm, making calculations of emission rates using Fick's Law unsatisfactory. Emission rates measured using closed flux chambers were at least one order of magnitude smaller from heavier‐textured arable soils than from lighter ones.Denitrification fluxes measured by field application of the acetylene inhibition technique were lowest in a clay loam, and highest in an alluvial sandy loam; this was attributed to a failure to achieve a satisfactory distribution of acetylene in the heavier soil. Denitrification rates in soil cores generally exceeded measured surface fluxes; incubation at decreased oxygen concentrations typical of those measured in the field produced a further significant increase. Core incubation should be used as an alternative toin situfield measurement only if the oxygen concentration in the incubation vessels is adjusted to mimic that in the field; otherwise denitrification rates may be significantly underesti

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1991.tb00414.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

SUMMARYAmmonia losses after surface application of fresh chicken slurry (15% solids) and anaer‐obically stored chicken slurry (10% solids) to a silty clay soil (pH 6.9) at a rate equivalent to 34 m3ha−1were studied in a laboratory incubation experiment. Total NH3‐N losses amounted to 29% of the initial uric acid‐N+urea‐N+NH+4‐N content of the fresh slurry and 28% of the initial NH+4‐N content of the anaerobic slurry. Peak rates of ammonia volatilization took place between 24 h and 48 h after application of the fresh slurry and within 5 h of application of the anaerobic slurry. The addition of CaCl2at a rate of 36 mg Ca g−1(dry wt) slurry decreased peak rates of ammonia volatilization from the fresh slurry by 73% and total losses by 37%. The decrease in total ammonia losses through CaCl2addition to the anaerobic slurry was only 8 %. The addition of CaCl2decreased CO2output from both slurries through precipitation of HCO3−as CaCO3, thereby removing a source of alkalinity from the solution. The failure of the CaCl2addition to decrease significantly ammonia losses from the anaerobic slurry suggested that HCO3−was an important source of alkalinity driving ammonia volatilization in the fresh slurry, but not in the anaerobic slurry.CaCl2, addition did not affect urea hydrolysis, nor net nitrogen mineralization. The decrease in ammonia loss achieved through CaCl2addition was however not associated with a parallel increase in ammonium concentrations in the soil. Further experiments showed that the ammonia retained by the CaCl2, was probably fixed by the soil and rendered non

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1991.tb00415.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

SUMMARYStudies on phosphate sorption and availability in some north‐east Nigerian soils showed that phosphate adsorption and inorganic‐P concentrations increased considerably after the soil was heated either in a furnace or during the field‐burning of straw. The increase in phosphate adsorption after heating was thought to be caused by an increase in free Fe and A1 oxides, whereas the high contents of exchangeable Ca and possibly carbonates and hydroxyl ions in the ash were probably responsible for the increase in phosphate sorption after field‐burning of straw.Investigations into the availability of P to maize over a 7‐d period of growth showed that there was no significant nutritional benefit from the P released after soil heating. The effect of heating was to increase P sorption and so reduce P in solution and P ava

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1991.tb00416.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

SUMMARYThe dissolution of a reactive phosphate rock (Gafsa, GPR) was evaluated in a range of UK soils which varied considerably in calcium (Ca) status and in a soil that had been amended with different amounts of a cation exchange resin (CER) to provide a Ca sink of varying size. As expected, but not apparently previously reported, increasing solution Ca concentration caused a decrease in the dissolution of GPR, consistent with the solubility product principle. At 40 d, the extent of GPR dissolution was correlated more closely with soil solution Ca concentration (r=−0.91) than with either the number of unoccupied exchange sites for Ca or the Ca‐exchange capacity (CaEC) of the soil (r=0.61 andr=−0.35, respectively). Unoccupied exchange sites for Ca were only effective in influencing GPR dissolution when solution Ca concentration was sufficiently low (<1 mmol dm−3) for the sites to be operating on the well‐buffered portion of the Ca‐exchange isotherm. The combined effects of an initial low solution Ca concentration and the presence of unoccupied Ca exchange sites caused the relationship between GPR dissolution and solution Ca concentration to become curvilinear, whereby the proportion of GPR dissolved at 40 d could be related to the initial soil solution Ca concentration by an exponential equation. A similar interaction was obtained for the relationship between GPR dissolution and CaEC (operating at solution Ca concentrations ≥0.6 mmol dm−3) following the addition of CER to the soil. The effectiveness of the additional sites for Ca in maintaining the product of ionic concentrations below the solubility product of GPR was such that the amount of GPR dissolved at 40 d correlated linearly and strongly (r= 1.00) with the CaEC of the so

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1991.tb00417.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

SUMMARYZinc movement in soils is influenced by soil pH, the presence of organic chelators, the total quantity of Zn in the soil and by root exudates. The effect of these factors on Zn uptake by a single plant root was simulated mathematically by Bar‐Yosefet al.(1980). The objective of this paper was to validate this simulation model and evaluate the relative importance of soil chemical properties, the stability of Zn complexes and the soil pH in determining Zn transport in soil and absorption by plant roots. To avoid problems of soil and plant variability, an artificial root, namely a ceramic tube through which solutions of known composition flowed, was used. The soil was a montmorillonite‐sand mixture of known Zn adsorption characteristics. The model satisfactorily described the decline in net Zn influx into the root (Fznas soil pH increased or as total Zn in soil (Qzn) decreased, and also describedFzn, as a function of time. Addition of fulvic acid (FA) to the soil decreasedFzn. The decreased uptake rate stemmed from the lower permeability of the root to the large Zn‐FA molecule. When the pH of the solution that flowed inside the tube was decreased from 5.0 to 2.0, thus generating a greater efflux of H+by the roots,Fzn, increased four‐to six fold, depending on the time. The model satisfactorily described the decline inFzn, as the clay fraction in the soil increased, while maintaining the same quantity of Zn per volume

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1991.tb00418.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

SUMMARYA quick, convenient and robust method is presented for measuring the effective diffusion coefficients of non‐sorbing solutes in soil. The method estimates the effective diffusion coefficient from a measured diffusion profile by optimizing the solution of a numerical simulation model describing the experimental system. The method was used to measure the effective diffusion coefficients of compounds found in root exudate

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1991.tb00419.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

SUMMARYA mathematical model was developed which was capable of simulating the diffusion of compounds with a concentration‐dependent diffusion coefficient, by virtue of their sorption on the solid phase of the soil. Methods were developed which allowed the sorption characteristics and the effective diffusion coefficient of several organic compounds to be inferred from their measured diffusion profile

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1991.tb00420.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

SUMMARYA description of the partitioning of humic substances (HS) between the solid and solution phases of acid organic soils is proposed, based on the opposition of hydrophobic and hydrophilic properties. Soil HS are considered to be of two types, mobile, i.e. potentially transferable to the soil solution (HSM), and immobile (HSI). The HSM consist of a series of fractions, each with the same ion‐binding properties, but differing in hydrophobicity. Partitioning of HSM between the solid and solution phases depends upon the net humic charge (Z), which is determined by the binding of protons and other cationic species. For each fraction, the extent of transfer to the solution phase increases asZbecomes more negative. The most hydrophilic HSM require only a small negative charge for transfer to the solution phase to be favoured, while the most hydrophobic require the development of a large negative charge. A mathematical version of the model, combined with an existing model of ion‐binding by HS, can explain reasonably well the release of HS from agitated aqueous suspensions of organic soil samples. The model also explains the release of HS when the solution phases of organic soil suspensions were repeatedly replaced with NaCl solut

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1991.tb00421.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

SUMMARYRetention of ethylene glycol monoethylether (EGME) and ethylene glycol (EG), and sorption of nitrogen and water vapour, were studied on a wide range of soils from New Zealand and Fiji. EGME retention was mainly affected by the amount of EGME liquid present in the desiccator, the interaction with the desiccant (CaCl2), the amount of residual water in the samples, and the time taken to establish end‐points. The extent to which each of these factors influences the weight of EGME retained was different for each sample. Surface areas from nitrogen sorption (BET) were not related to those derived from EGME retention in the same way for all soils; EGME retentions did not vary systematically with clay mineralogy. A constant conversion factor cannot be used to convert retentions of polar liquids (EGME, water and EG) to specific surface values, and retention data by itself cannot be used to measure the absolute surface areas of soil

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1991.tb00422.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY