ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1985.tb00308.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

SUMMARYSimple theory has been developed and illustrated elsewhere which allows estimation, firstly, of the mean depth of solute penetration from any sequence of infiltration and evapotranspiration events, and secondly, of the apparent dispersion about this mean depth used as a Lagrangian coordinate system. This theory was used to analyse and interpret the time patterns of leachate concentrations of NO3‐N and Cl of a field lysimeter with a potato crop receiving four fertilizer applications and numerous inadvertent N and Cl applications by irrigation with groundwater. The assumption of superposition of estimated solute concentrations was employed in the analysis, yielding results consistent with the data. The analysis has quantified the leaching loss from each fertilizer applicatio

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1985.tb00309.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

SUMMARYThe charge characteristics of A1or Ap and B2horizon samples of total 23 Ultisols, Alfisols and Oxisols in Korea and Thailand were studied by measuring the retention of NH4+and NO3−at different pH values (4–8) and NH4NO3concentrations (0.1–0.005m). The magnitude of their negative charge (σ−; meq/100g) was dependent on pH and NH4NO3concentration (C;m) as represented by a regression equation: log σ−=apH +blogC +c. The values of the coefficienta(0.04–0.226),b(0.03–0.264) andc(–0.676–1.262) were correlated with the kinds of the soil and horizon and with the region where the soil exists. The retention of NO3−was less than 1 and 2–3 meq/100 g for the A1or Ap and B2horizon samples, respectively.The sum of exchangeable base and Al (‘effective’ CEC) was close to and higher than the magnitude of permanent charge (=σ−measured at pH = 4.3 and at C = 0.005m) for one‐third and two‐thirds of samples, respectively. A σ−value of 16 meq/100 g clay at pH = 7 and C = 0.01mwas found appropriate to separate the B2horizons of Thai Ultisols and Oxisols from those of Korean Ultisols and Alfisols. Korean Alfisols and Ultisols and Thai Ultisols were distinguished from each other on

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1985.tb00310.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

SUMMARYThe distribution of ethylenediaminetetraacetic acid (EDTA)‐extractable Cu concentration levels in 3653 samples from 725 Scottish soil profiles is reported. The derived mean for the full set of data is 0.86 mg kg−1and the normal range 0.08–9.8 mg kg−1. The relation of extractable Cu concentration to that of total Cu and to some other soil variables is also examined. Extractable Cu contents decrease with increasing depth over the first 50 cm and are almost constant below this.The correlation between total and extractable copper (r=+ 0.453) is statistically highly significant (P<0.001). The extractability (i.e. the percentage of total Cu extractable by EDTA) has also been considered in relation to the other soil variables. Extractability is inversely related to ash content though the relationship is not linear. Extractability is enhanced under conditions of impeded drainage but there is no indication that it is related to clay or sand contents.Approximately 18% of the arable topsoil samples contain levels of extractable Cu which are inadequate to supply the nutritional requirements of cereal crops and approximately 79% contain levels inadequate to support herbage with a Cu content sufficient to supply the requirements of grazing

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1985.tb00311.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

SUMMARYPotassium release from saturated spherical aggregates of three clay soils to Ca‐resin was measured and compared with release in suspensions (Talibudeenet al., 1978). The diffusion coefficient for K was calculated from measurements of the tortuosity factor using36Cl, volumetric water content and buffer power. Release of K is in the order: suspensions>2–3 mm>6–8 mm aggregates. A computer model incorporating diffusion analysis and release of K shows that in the aggregates the rapidly diffusing exchangeable K, Kex, is best measured by the extrapolated intercept of a desorption isotherm (24 h equilibration), and is 8–55% less than that extracted by NH4OAc leaching. Release of K within the aggregates (Knex, a fraction approximating to Talibudeen's peripheral K) is delayed until after about 95% of Kexhas been depleted which takes 1–2 days. The effective release rate of Knexinside the aggregates is ∼ 17% less than in soil suspensions. Diffusion imposes only small limitations on the release from aggregates of Knex. This rate of release depends on the frequency of re

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1985.tb00312.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

SUMMARYA model based on measurements of potassium release from spherical aggregates (Heming&Rowell, 1985, Part I) has been used to predict release from larger aggregates, for longer times, drier soils and varying diffusion coefficients. The model has been adapted to predict supply to a single root from a soil cylinder and compared with measured uptake by onions. A ‘supply index’ shows likely restrictions in the availability of exchangeable K and in the rate of supply of non‐exchangeable K resulting from diffusion limitations over a 4 week period for (i) aggregates covered with a dense roots system, and (ii) roots growing at known densities. For this period diffusion alone should not limit exchangeable K uptake in the field if the root density is at least 3.5 cm/cm3: at 0.9 cm/cm3about 50% may be unavailable. The supply rate of non‐exchangeable K increases with root density and may be important for high‐demanding crops in dr

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1985.tb00313.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

SUMMARYTwo grass species,Holcus lanatusandDeschampsia flexuosa, were grown in soil containing available nitrogen at 4 μg g−1(‘Low N’) or 58 μg g−1(‘High N’), in a controlled environment. Water was supplied via an auto‐irrigation system, which also minimized the vertical redistribution of soil nutrients, particularly NO3−. Growth, root morphology and distribution, and N uptake were measured during a 70‐day period.H. lanatusproduced more dry matter thanD.flexuosain the high N treatment. Yields were similar in both species in the low N treatment. The growth ofH. lanatusin the low N treatment was not limited by a complete exhaustion of soil N. Root density ofH. lanatuswas likely to have been inadequate to allow this species to attain its maximum potential N‐inflow rate. Thus, N uptake per plant and dry matter production were restricted. The growth ofD.flexuosawas not limited by the low N treatment, compared with that in the high N treatment. This was attributed to its low maximum potential relative growth rate and, hence, its low demand for N compared withH. lanatus, rather than to any major ‘compensatory’ adjustments in root morphology o

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1985.tb00314.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

SUMMARYIn thin sections of a cemented Bs horizon, allophane is present as isotropic, or weakly anisotropic, transparent, yellow, commonly fluorescent gel deposits, which line or fill voids, cement sand and silt, and form pseudomorphs of root structures. Atomic ratios of Si: Al range from 1: 2.2 to 1: 3.7 in pale deposits, but drop to 1: 8.8 in regions of organic staining. Fe: Al atomic ratios in transparent deposits range from near zero to 0.4. The local uniformity of the gels indicates that the allophane, with associated iron oxides, is deposited from solution, and is not formedin situfrom a precipitated organic complex, or by weathering of mineralsin situ.Mineralogical evidence indicates that the origin of the allophane is related to intense acidic weathering of plagioclase and biotites in the Eg and Bhg horizons. A fibrous morphology indicative of imogolite is seen under the scanning electron microscope only in critical point dried specimens.It is proposed that the cracked coatings characteristic of cemented Bs horizons can be interpreted as allophanic deposits, associated with varying amounts of clay and iron oxide, and impregnated with varying amounts of fulvic acids. Such deposits cannot be taken as evidence for the migration of Al and Fe as organic complexes.

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1985.tb00315.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

SUMMARYA mathematical model for soil profile evolution is developed in three parts; respectively for the weathering profile, the organic profile and for the inorganic profile associated with nutrient cycling. Processes modelled are percolation, equilibrium solution, leaching, ionic diffusion, organic mixing, leaf fall, organic decomposition and mechanical denudation. In each sub‐model some of these processes may be neglected, and time‐scales differ, so that they are best separated. Each leads to a second‐order linear partial differential equation with non‐constant coefficients. Equilibrium profiles are derived for the simplest cases, and numerical models exemplify profile evolution in more realistic cases. Modelled weathering profiles generally show a zone of near‐constant composition at the surface, with saprolite developing in deep profiles. Nutrient‐cycling profiles show the variable development of B‐horizons, and may be classified according to the relative depths of rooting, organic soil, and organic mix

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1985.tb00316.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

SUMMARYThe recuperation of the soil during bush fallows after a period of cultivation is an important part of the success of shifting cultivation in the lowland humid tropics. However, the sources of the nutrients which enable the observed rapid growth on apparently exhausted soils has never been satisfactorily explained. Some soils from the Manaus region of Brazil have been examined in an attempt to identify reserves of potassium. X‐ray diffraction, physical and chemical analyses, and microcalorimetric measurements of K‐Ca exchange show that small reserves of K occur in 2:1 clay minerals which exist in trace amounts in the soils. The results suggest that the clay fraction of the soil may play a more important role in nutrient supply than previously realized. The reserves are considered in terms of the land use of the a

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1985.tb00317.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY