摘要:

SUMMARYLarge undisturbed soil cores (20 cm diam. × 25–30 cm long) were irrigated at rates of 0.5–4 cm h−1with 0.005 M CaCl2solution labelled with3HOH. The cores were used at varying initial water contents and flow in all cases was unsaturated. Breakthrough curves for Cl and3HOH were markedly asymmetric and unlike those reported for columns of packed aggregates. The data could be satisfactorily described using a density distribution function of the logarithm of cumulative drainageD.The mean and standard deviation of InDwere estimated by a curve‐fitting procedure from Cl and3HOH effluent concentrations in each core. The mean pore water velocity and fraction of the soil water that participated in solute transport (the mobile volume) were also calculated.The apparent velocity of Cl movement was always greater than that of3HOH which suggested that the mobile volume involved in convective and diffusive transport of Cl was less than that for3HOH. We suggest that Cl and3HOH diffused at different rates out of flowing water films in a relatively few large conducting channels into essentially immobile water within the surrounding soil matrix. The difference in mobile volume for Cl and3HOH was used to calculate the perimeter of voids in any horizontal cross‐section of the soil through which water flowed, assuming a planar interface between the mobile and immo

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1984.tb00271.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

SUMMARYThe objective of this work was to determine the fate of fertilizer nitrogen (labelled with nitrogen‐15) applied to an undisturbed shallow soil overlying Chalk contained in 10 lysimeters (80 cm diameter, 135 cm deep). Measurements are reported of the nitrogen uptake by four spring barley crops and the rate and extent of leaching of nitrate beyond the roots. The crops were fertilized with 0, 80 or 120 kg N ha−1in each of four years, but only the first application in 1977 was labelled with nitrogen −15. Rainfall and irrigation approximated to the long‐term average, but in two treatments dry or wet spring conditions were imposed for the 10 weeks after sowing the first crop in 1977. The dry matter and grain yields of the spring barley crops varied from year to year in the ranges 8.7–14.0 t ha−1and 3.5–6.1 t ha−1respectively. The total nitrogen harvested in the crop approximated to the amount of nitrogen applied in each year with an apparent recovery of fertilizer in the range 38–76%. The recovery of nitrogen derived from fertilizer (labelled with nitrogen‐15) was 46–54% in the first crop and after 2 years rapidly declined to below 1%. The total amount of nitrogen‐15 labelled fertilizer recovered in four barley crops was 49–57% of that applied.Mean annual nitrate concentrations in water draining from the base of the lysimeters were in the range 11.8–26.7 mg N 1−1and did not differ significantly between nitrogen fertilizer treatments (0, 80 and 120 kg N ha−1a−1). In all treatments nitrate concentrations varied considerably within each growing season, with a cycle of peaks and troughs. Annual losses of nitrate were in the range 39–128 kg N ha−1, and the mean annual losses over the 4 years varied between lysimeters from 65 to 83 kg N ha−1. Nitrogen‐15 labelled nitrate was detected in the first drainage water collected in autumn following its spring application, 5 months earlier. Recovery of fertilizer‐derived nitrogen in drainage water was greatest during the winter following the second barley crop, and was 3.4–3.7% of the nitrogen‐15 applied. Over the 4 years of the experiment 6.3–6.6% of labelled fertilizer was accounted for in drainage water, represe

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1984.tb00272.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

SUMMARYFour successive spring barley crops were grown in monoliths of a shallow soil overlying Chalk, contained in lysimeters. After harvest of the fourth crop, 25% of the nitrogen‐15 labelled fertilizer applied 4 years earlier was found remaining in the roots and soil. Of this, 73% was present in the upper 30cm of the profile. From the amounts of fertilizer derived nitrogen that remained at the beginning of each cropping season we estimate that 5–6% of the residual nitrogen‐15 turned over each year, representing a net release of 20% of the labelled nitrogen contained in the microbial biomass. Mineralization of the total biomass at the same fractional rate would release 120 kg N ha−1a−1. This estimate is supported by the difference between input and outputs of total nitrogen during the experiment of 76–94 kg N ha−1a−1in fertilized lysimeters and 129kg N ha−1a−1in unfertilized control lysimeters. The total recovery of the applied labelled nitrogen was 81–87%. The nitrogen not accounted for was taken to be lost by denitrification of nitrate to dinitrogen, as no nitrous oxide emissions were detected during the experiment. Laboratory studies in aerobic and anaerobic conditions in presence of acetylene confirmed that 10–20% of the applied nitrogen‐15 could have been

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1984.tb00273.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

SUMMARYResults are presented from a 3‐year investigation into nitrate leaching from grassed monolith lysimeters treated with double (15NH415NO3) or single (15NH4NO3) labelled ammonium nitrate at three rates, 250, 500 and 900 kg N ha−1a−1. Over the 3 years of the experiment, 0.14%, 3.1% and 18.1% of the applied fertilizer was recovered in the leachate at 250, 500 and 900kg N ha−1respectively. This represented 9%, 39% and 75% of the overall nitrate leaching at the three application rates. A significant proportion of the fertilizer leached as nitrate at the three application rates was derived, via nitrification, from the fertilizer ammonium. Increasing fertilizer applications caused a rise in the leaching of both soil and fertilizer derived nitrogen, although whether the increase reflected a true priming effect was no

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1984.tb00274.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

SUMMARYPreliminary studies using27Al n.m.r. of well characterized size fractions containing imogolite from an Andosol are reported. They demonstrate that27Al n.m.r. is a useful complementary tool to X‐ray fluorescence methods for the detection of four‐and six‐fold co‐ordination of aluminium in soils. Whereas the X‐ray method depends on interpolating between standards, this is unnecessary in the n.m.r. method since four‐ and six‐fold coordinated aluminium are clearly resolved. The results demonstrate how aluminium co‐ordination changes in size fractions from the Andosol and confirm that all aluminium in imogolite is in six‐fold co‐ordination. It is also suggested that the Al‐O bond distance i

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1984.tb00275.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

SUMMARYPreliminary studies are reported on a soil and a litter fraction which have the aim of exploring the potential of two‐dimensional13C nuclear magnetic resonance spectroscopy for the analysis of soil organic matter structure. It has been shown that contour plots can be obtained in which one co‐ordinate gives chemical shift information and the other the magnitude of the dipolar interaction. For aromatic and oxygenated aliphatic carbon, the latter parameter is a measure of the degree of protonation. Hence the method is useful for distinguishing between soils containing highly substituted and condensed aromatic structures and those with protonated aromatic carbon. Likewise, it is possible to distinguish between soils containing dioxygenated carbon which is. protonated (e.g. ket

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1984.tb00276.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

SUMMARYEquilibrium calculations have been carried out at 25°C and an ionic strength of 0.04 to determine the predominant metal binding sites on a well‐characterized fulvic acid for magnesium(ll), calcium(ll), manganese(ll), iron(lll), copper(ll) and zinc(II). Statistical estimates of the concentration of 14 sites are obtained from a random molecular model of fulvic acid. Protonation and metal formation constants are estimated from those of simple model ligands and corrected to the above conditions. Results indicate the importance of phthalate sites for all metals except iron(III), salicylate sites for iron(lll) and acetylacetonate sites for copper(ll). Iron (III) ions are found to form ML2type complexes extensively. The affinity of the metal ions for fulvic acid as a whole is found to decrease in the order iron(III)>copper(II)>zinc(II)>manganese(Il)>calcium(II)>magnesium (I

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1984.tb00277.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

SUMMARYThe stability of aggregates from 26 soils selected from agricultural areas was measured by wet‐sieving and the results correlated with sand, silt, clay, nitrogen, organic matter and iron contents and with cation exchange capacity. Highly significant correlations were obtained for the relationships between aggregate stability and organic matter and some properties associated with it. No other soil constituent investigated had a significant relationship with aggregate stability, indicating that organic matter is mainly responsible for the stabilization of aggregates in these soils.The relationships between aggregate stability, and organic matter content plus some of its component fractions were examined in more detail using 120 soils. Total organic matter, total carbohydrate and humic material extracted by various reagents each gave highly or very highly significant correlations with aggregate stability. However, whilst it was not possible to distinguish whether any one organic component was more important than another, the results indicate that soil organic matter levels can be used diagnostically to identify soils which may show problems of structural instabilit

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1984.tb00278.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

SUMMARYThe decomposition of rice and barley straw saccharides under field conditions was well represented by the first‐order kinetics model ofYt=C1e−k1t+C2e−k2t, whereYtis the remaining amount at timet, k1andk2are the decomposition rate constants (time−1) for the labile fraction (C1) and the non‐labile fraction (C2), respectively. About 82% of the total saccharide content of the rice straw was in the labile fraction with a rate constant 0.64–0.81, the values for the barley straw being 70–92% and 0.50–0.61, respectively. The non‐labile fraction appeared to persist for a long time, with a half‐value period of 9–59 months. Barley straw and its saccharides decomposed at a slower rate than rice straw. Much more favourable initial decomposition was observed in a paddy field than in an upland field.Mannose, fucose, rhamnose and ribose were synthesized in parallel with the flush of decomposition

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1984.tb00279.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

SUMMARYFe and Al were extracted by 0.1 M pyrophosphate solutions from six replicate samples of seven soils by different, widely‐used techniques, viz. those of the Soil Survey of England and Wales, the Canadian Soil Survey and the United States Soil Conservation Service. The effects of K‐ versus Na‐pyrophosphate solution, and of a difference in the pH of the latter were also investigated. All the techniques gave both different, and a wide spread of, values for Fe and Al in all soils. No one technique was consistently the least variable for both elements. Replicate determinations using each technique were so variable that comparison of results obtained by the different techniques cannot be made with confi

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1984.tb00280.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY