摘要:

SUMMARYSamples of 1–2 mm crumbs from a clay loam under permanent pasture were equilibrated at ‐5 kPa water potential then compacted to varying degrees. Gas diffusion coefficientsD, (hydrogen through air), were measured immediately on compaction, again after re‐equilibration at ‐5 kPa, then at other water contents between saturation and dryness. The relationship between diffusion coefficient and air content, was, as elsewhere, in two parts (dD/dsmall for drainage of pores within crumbs; large for pores between crumbs), but the transition from one part to the other occurred at smaller air contents with increased compaction. The air content at whichDapproached zero as the samples wetted was greatest in the loosest soil. Compaction from a bulk density of 0.86–1.29 g cm−3decreased the relative diffusion coefficient,D/D0(D0is the diffusion coefficient without impedance), from 0.35 to 0.22 (by 38%) at complete dryness, but from 0.19 to 0.035 (by 82%) in the soil initially at ‐5 kPa. On re‐wetting and re‐equilibrating at −5 kPa,D/D0decreased further to 0.008 (total 97%) because of extra water held in the now smaller pores of the compacted soil.No single relationship betweenD/D0and fitted the results for

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1984.tb00253.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

SUMMARYAcetylene blockage was evaluated as a method for measuring losses of N2O + N2from two Denchworth series clay soils. The denitrification potential in anaerobic, dark incubations at 20°C with nitrate (equivalent to 100 kg N ha−10–20 cm depth), maximum water holding capacity, and acetylene (1%), was equivalent to 32 ± 11 and 39 ± 6 kg N ha−1per day for the two 0–20 cm soils and was positively correlated with carbon content (r= 0.98). After 4 days N2O was reduced to N2in the presence of C2H2.In April 1980 following irrigation (24 mm) and applications of ammonium nitrate (70 kg N ha−1) and acetylene, the mean nitrous oxide flux from soil under permanent grass was 0.05 ± 0.01 kg N2O‐N ha−1per day for 8 days.In June 1980, the losses of nitrogen from cultivated soils under winter wheat after irrigation (36 mm) and acetylene treatment were 0.006 ± 0.002 and 0.04–0.07 ± 0.01 kg N ha−1per day respectively before and after fertilizer application (70 kg N ha−1). The nitrous oxide flux in the presence of acetylene decreased briefly, indicating that nitrification was rate d

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1984.tb00254.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

SUMMARYAnalysis of the results of 104 personnel who determined the particle size distribution of 16 different soil‐size materials indicated that there was an effect of subsample preparation. Subsamples prepared using a chute splitter tended to be coarser than those prepared by coning and channelling. This effect was observed for material retained on 425 μm and 75 μm sieves from a variety of soil types. The results confirm those obtained on artificially prepared mixes. The conclusion is that the chute splitter is a more reliable method for obtaining the test portion than coning and channell

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1984.tb00255.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

SUMMARYThe rates of diffusion of chloride, sulphate and water, labelled respectively with36Cl,35S and3H, and unlabelled nitrate, were measured in small cylindrical Chalk monoliths. Using a simple mathematical model, diffusion coefficients were calculated to provide a basis for comparing the movement of these substances through Chalk rock in the absence of hydrostatic pressure gradients. The diffusion coefficients of chloride and nitrate were similar, with a range of values (0.52–3.23 × 10−6cm2s−1) and (0.53–3.20 × 10−6cm2s−1) respectively. These were slightly less than for tritiated water (0.60–3.51 × 10−6cm2s−1), while the coefficient for sulphate was about half that of the others (0.28–1.47 × 10−6cm2s−1). The coefficients indicate the absence of any interact

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1984.tb00256.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

SUMMARYThe different forms of phosphorus (P) in 0.5 m sodium hydroxide extracts of soils from long‐term field experiments at Rothamsted were characterized by31P‐nuclear magnetic resonance spectroscopy (NMR).The extract from an old grassland soil (pH 4.6) from a plot of the Park Grass Continuous Hay Experiment that had received no fertilizer or lime for at least 125 years contained the following forms of P: inorganic orthophosphate (22% of the extracted P), orthophosphate monoesters (49%), orthophosphate diesters (14%), phosphonates (3%), pyrophosphate (4%) and two unidentified forms of P (7%). The soil extract from a Park Grass plot given inorganic phosphate fertilizer (35 kg P ha−1) annually for 121 years contained the same forms of P and, in addition, a small amount of polyphosphate. There was also evidence of an increase in the orthophosphate monoester fraction.Another old grassland soil, of pH 6.1, contained more total and organic P than Park Grass but the extract contained fewer forms of P: inorganic orthophosphate (14% of the extracted P), orthophosphate monoesters (39%), orthophosphate diesters (34%) and an unidentified form (13%). An area of this grassland that had been ploughed up 20 years previously, and kept bare since, contained less organic P. The extract contained less of the phosphate diesters but the more stable monoesters remained relatively unch

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1984.tb00257.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

SUMMARYPrevious solution13C n.m.r. studies of soil organic matter have been confined to isolated humic or fulvic acid fractions. A study of 10 crude alkaline extracts from five New Zealand topsoils has now shown that such purification is unnecessary. Spectra were not noticeably broadened by co‐extracted iron in concentrations up to 2 mg cm−3. Optimized pulse parameters were similar to those reported for a solution of a purified humic acid. Relaxation results support a generalized model for humic material, in which aromatic structures, carbohydrates, amino acids and polymethylene chains are linked together to form flexible macromolecules. Relative contributions from each component varied from soil to s

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1984.tb00258.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

SUMMARYSamples of solutions from soils contaminated with lead as a result of three different processes: natural weathering and dispersion from an ore body, mining and smelting, and sewage sludge‐amendment to land, were fractionated on Sephadex gels. Solutions from the sludge‐amended soil, dried sludge and calcareous mine soils were found to contain a proportion of lead eluted at the exclusion limit of the gel, accompanied by a peak in U.V. absorbance, implying the occurrence of a high molecular weight organo‐lead complex. This fraction was proportionally highest in the solution from the dried sludge sample; however, low molecular weight organic peaks were also accompanied by elution of Pb in all samples except that from the low pH, naturally contaminated site. Association of Pb with organic matter was observed to be greater in samples of soil solution with a higher initial pH and this may be related to increased stability constants for Pb‐organo complexes at hi

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1984.tb00259.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

SUMMARYInfrared absorption spectra of phosphate sorbed on alumina gel were obtained by subtracting the diffuse reflectance infrared (DRIR) spectra of alumina gel from those of phosphated alumina gel. The positions of the absorption bands due to P·O stretching vibration were little affected by the change in pH and the amount of phosphate sorbed. These absorption bands were similar to those for aluminium phosphate gel. The sorption product of phosphate on alumina gel was amorphous by X‐ray diffraction. Na+and Cl−adsorption properties of alumina gel tended towards those of aluminium phosphate gel with phosphate sorption. It was concluded that the state of phosphate sorbed on alumina gel is similar to that of aluminium phosphate

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1984.tb00260.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

SUMMARYSoils from Denmark and Tanzania were extracted with ammonium acetate (controls), EDTA to dissolve amorphous iron oxides, and dithionite‐EDTA (DE) to dissolve crystalline iron oxides. The amounts of chloride adsorbed by the extracted soils from 1 m NaCl at pH 5 and pH 7 were determined.The differences (ΔCl) between chloride adsorption at pH 5 and pH 7, attributed to variably charged groups, decreased when iron oxides were removed by EDTA and DE extraction. Close correlations (P>0.001), with negligible intercepts, were found (i)between EDTA‐extractable iron (amorphous iron oxides) and the decrease in ΔCl following EDTA extraction, and (ii) between the difference between DE‐extracted iron and EDTA‐extractable iron (crystalline iron oxides) and the further decrease in ΔCL following DE extraction.The difference between ΔCl for acetate‐extracted and DE‐extracted samples was calculated from the contents and specific surfaces of amorphous and crystalline iron oxides, together with ΔCl per m2for synthetic iron oxides. Calculated and measured values were in very good agreement, indicating that soil iron oxides, in relation to chloride adsorption, may be treated as if they consist of on

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1984.tb00261.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

SUMMARYSorption isotherms were obtained by a continuous‐flow method for the interaction of hydrazine hydrate with freeze‐dried hydrogen‐, aluminium‐ and calcium‐exchanged humic acid preparations in aqueous suspensions at pH 4. The application of the continuous‐flow method is outlined and the fit of the isotherms to three sorption equations is examined. Microcalorimetry was used to measure directly the differential enthalpies of reaction as functions of sorptive concentrations. Exchange by hydrazinium ions of the exchangeable cations on the humates, chemisorption by interaction of hydrazine with humate carbonyl groups, and non‐specific sorption involving weakly‐ and strongly‐held hydrazinium ions and hydrazine molecules are shown to be the major sorption processes in these systems. The relative importance of each of these processes for the different hydrazine/humate systems is discussed, and the influence of the exchangeable cation on humate reactiv

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1984.tb00262.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY