ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1993.tb02320.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

SUMMARYNumber‐size distributions (i.e. particle‐ and aggregate‐size distributions) have historically been used as indicators of soil structure, and recent work has aimed to quantify this link using fractals to model the soil fabric. This interpretation of number‐size distributions is evaluated, and it is shown that a number‐size relation described by a power law does not in itself imply fractal structure as suggested, and a counter example is presented. Where fractal structure is assumed, it is shown that the power‐law exponent, φ, describing the number‐size distribution cannot be interpreted as the mass‐fractal dimension, DM, of the aggregate. If the probability of fragmentation is independent of fragment diameter, then the exponent may be identified with the boundary dimension, DB, of the original matrix. If, however, as is likely, this probability is scale‐dependent, then φ may over‐ or under‐estimate the boundary dimension depending on whether the fragmentation probability increases or decreases with fragment size. The significance of these conclusions is discussed in terms of the interpretation of number‐size distributions, and alternative methods for quantifying and interpreting soi

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1993.tb02321.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

SUMMARYA method is proposed which follows Darrah's experimental procedure and takes advantage of a mathematical solution provided by Carslaw&Jaeger to estimate the diffusion coefficients of adsorbed and non‐adsorbed solutes in soil.The method requires only the values of the concentration of the solute at the input face of a uniform column of soil, Cs, and of the total amount, Qt, that has entered the soil after a specified time during which the surface of the block is in contact with a thin porous pad containing a known initial amount of solute, Q0, at concentration C0, expressed in the same units as Cs. In the Cs/C0vs. Qt/Q0space there is a unique relationship between the effective diffusion coefficient, De, of the solute in the soil and the contact conductance for this solute,h, between the pad and the soil surface.The proposed procedure is firstly to determine De, and h for a non‐adsorbed solute in the experimental soil using the experimental values of Cs/C0and Q/Qfor that solute. This value of De, gives the diffusion impedance factor for the solute in the soil,f, which is assumed also to apply to adsorbed solutes. A first estimate of the effective diffusion coefficient of an adsorbed solute,1Dea, is then made usingfand the diffusion coefficient of the free solute in water, DL, obtained from the literature (i.e.1Dea= DLf). Only if the solute is weakly adsorbed will the values of Cs/C0, and Qt/Q0lie in Cs/C0, vs. Qt/Q0, space as defined by1Deaand the contact conductance,h. Instead a second space relating Cs/C0and Qt/Q0, is now constructed from nominated values ofhand De, where De, is defined in terms of1Dea, the adsorption coefficient,F, and the volumetric moisture content of the soil, θ. The position of the experimental values of Cs/C0, and Qt/Q0within this new space defineshand the actual De, andFof the solute as it diffuses and is adsorbed in the soil.The advantages and limitations of the method are discussed. In particular, the method assumes that the adsorption process is linear and revers

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1993.tb02322.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

SUMMARYA functional model designed to simulate the transport of non‐interactive solutes through macroporous soil is described. The concept of mobile and immobile water is used but the pore volume available for mobile water is partitioned to allow for flow through smaller water‐filled pores and rapid preferential flow through larger macropores and fissures. The general performance of the model under steady infiltration following an injection of solute is presented. The sensitivity of the output to variations in the model parameters is also discussed. A second paper compares the model with bromide and chloride leaching data on two texturally contrasting so

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1993.tb02323.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

SUMMARYThe performance of a functional leaching model (Hall, 1993) is compared with leaching data from two lysimeter experiments with soils of contrasting texture using sodium bromide and potassium chloride as the non‐reactive solutes. The model parameters are optimized using the solute elution curves as standards and compared with the physical properties of the soil. A good match with the measured discharge of both water and solute was achieved for both soils using the moisture release characteristics to define the pore volume available for mobile and immobile water. The results indicate that preferential flow takes place through even coarse‐textured soils but that there is negligible diffusive exchange of solute between water passing through the macropores and the rest of the s

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1993.tb02324.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

SUMMARYDrained and undrained grassland lysimeter plots were established in 1982 on a clay loam of the Hallsworth series at a long‐term experimental site in south‐west England. The plots were continuously grazed by beef cattle, and received fertilizer at either 200 or 400 kg N ha‐1per annum to the existing permanent sward, or at 400 kg N ha‐1to a new sward, reseeded to perennial ryegrass following cultivation. Drainage water was monitored at V‐notch weirs and sampled daily for the analysis of nitrate‐N. Seven years of data are presented (five years for the reseeded swards). On the drained plots a large proportion of the rainfall was routed preferentially down large pores to the mole drains, whilst on the undrained plots, drainage was mainly by surface runoff. The average quantities of nitrate N leached per year were 38.5, 133.8 and 55.7 kg ha‐1from the old sward that received 200 and 400 kg N ha‐1, and from the reseed that received 400 kg N ha‐1fertilizer, respectively. Ploughing and reseeding resulted in a two‐fold reduction in leaching, except during the first winter after ploughing, and twice as much leaching occurred after a hot, dry summer as after a cool, wet one. Nitrate concentrations in drainage from either drained or undrained plots were rather insensitive to rainfall intensity, such that concentration was a good predictor of nitrate load for a given drainage volume. The drainage volume determined the proportion of the leachable N that remained in the soil after the winter drainage period. Initial (peak) concentrations of nitrate N ranged, on average, from 55 mg dm‐3for the drained old sward that received 400 kg N ha‐1fertilizer, to 12 mg dm‐3for the undrained sward at 200 kg N ha‐1fertilizer input. Concentrations of nitrate N in drainage from similar, unfertilized plots rarely exceeded 1 mg dm‐3. The results suggest that manipulating the nitrate supply can lessen leaching and that the route of water through soil to the watercourse determines the maximum nitrate c

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1993.tb02325.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

SUMMARYThe fate of fertilizer sulphur (S) applied as single superphosphate (SSP) to grazed pasture was examined in a field experiment for a period of 18 months using35S‐labelled SSP. Four sites were selected on the basis of contrasting fertilizer history and land slope. The fertilizer histories since 1981 for the sites were 125 (LF) and 375 (HF) kg ha‐1a‐1SSP and the slope gradients were low (LS, 0‐12°) and medium (MS, 13–26°).The amount of fertilizer S taken up by pasture as a fraction of total applied was greater at the LF (12%) than the HF (6%) site, suggesting that pasture at the LF site depended more on fertilizer than pasture at the HF site. At the LF site, fertilizer application did not significantly increase leaching losses of S (13 and 8.6 kg S ha‐1for fertilized and unfertilized plots, respectively). At the HF site, fertilizer application significantly increased leaching losses of S (38 and 21 kg S ha‐1for fertilized and unfertilized plots, respectively). The amount of fertilizer S lost by leaching as a fraction of total applied was greater at the HF (20%) than the LF site (7.6%). Most fertilizer S remained as soil organic matter. Plant uptake and leaching losses of fertilizer S were greater in the first year after application. The amount of N lost by leaching was very small in terms of N cycled through soil‐plant system (1 to 6 kg N ha‐1). The majority (>80%) of the S and N taken up by pasture and lost by leaching was derived from the mineralization of soil organic matter and not from freshly

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1993.tb02326.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

SUMMARYThe relations between pH, different fractions of Fe and A1 and Na4P2O7‐soluble C and the amount of adsorbed SO2‐4were assessed by analysing 63 soil samples from 14 podsolized soils in Sweden. The amount of adsorbed SO2‐4was significantly better correlated with the calculated amount of the inorganic fraction of Fe and A1 oxides obtained by subtracting Na4P2O7‐soluble Fe and A1 from oxalate‐soluble Fe and Al than with the oxalate extraction alone. There was a close correlation between C and organically‐bound S in the Na4P2O7extract which shows that the C:S ratio of the extracted fulvic acids is about constant in the soils studied. It was found that, as the proportion of organically‐complexed Fe and Al increases, the ability of the soil to adsorb SO2‐4decreases. The amount of adsorbed SO2‐4expressed on the basis of the amounts of oxalate‐soluble Fe and Al was generally smaller in areas with low S deposition (<60 mmol m‐2a‐1). The ratio between pyrophosphate‐soluble C and oxalate‐extractable Fe and Al was negatively correlated with pH in water. It was concluded that Fe and Al associated with organic matter cannot adsorb SO2‐4and that the degree of this association is pH dependent. These observations have important implications regarding the effects o

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1993.tb02327.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

SUMMARYA new and simple method for nitrate analysis in soil extracts and soil solution is described. The method uses the second derivative of the direct ultra‐violet (UV) spectrum, available from most microprocessor‐controlled spectrophotometers with a UV source. Results with the proposed method were similar to those obtained by the cadmium‐reduction column and ion‐chromatographic methods. The main advantages of the proposed technique are that it is simple, rapid, accurate and requires no sample pre‐treatment, making it useful for routine analysis of large numbers o

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1993.tb02328.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

SUMMARYDistribution and plant uptake of soil Cd as influenced by organic matter and soil type were investigated in a greenhouse experiment. Three soils (a sand, sandy loam and clay loam) were used. The rates of organic matter in its moist state added were 0,20,40, 80, 160 and 320 g kg‐1of the air‐dried soil on mass basis. Ryegrass (Lolium multörum L.) was used as a test crop. Soil Cd was analysed by a sequential extraction technique and by extraction with 1 M NH4NO3and 0.005 M DTPA. The exchangeable fraction of Cd as determined by 1 M MgCl2in the sequential extraction procedure increased, whereas the Fe‐Mn oxidebound fraction decreased, with increasing levels of organic matter addition in all three soils. The dry matter yields of ryegrass were not affected by the addition of organic matter, but the Cd concentrations in both cuts of ryegrass decreased with increasing amounts of organic matter added. The plant Cd was highly but negatively correlated to soil CEC. At any level of organic matter addition, the decrease in Cd concentration of ryegrass was in the order: sand>sandy loam>cla

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1993.tb02329.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY