SSSAJ Journal of Natural Resources and Life Sciences Education
HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS
QUICK SEARCH:   [advanced]


     

This Article
Right arrow Abstract Freely available
Right arrow Figures Only
Right arrow Full Text (PDF) Free
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Services
Right arrow Similar articles in this journal
Right arrow Similar articles in ISI Web of Science
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Right arrow reprints & permissions
Citing Articles
Right arrow Citing Articles via HighWire
Right arrow Citing Articles via ISI Web of Science (33)
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Hallett, P.D.
Right arrow Articles by Young, I.M.
Right arrow Search for Related Content
PubMed
Right arrow Articles by Hallett, P.D.
Right arrow Articles by Young, I.M.
GeoRef
Right arrow GeoRef Citation
Agricola
Right arrow Articles by Hallett, P.D.
Right arrow Articles by Young, I.M.
Soil Science Society of America Journal 65:184-190 (2001)
© 2001 Soil Science Society of America

DIVISION S-6-SOIL & WATER MANAGEMENT & CONSERVATION

Subcritical Water Repellency of Aggregates from a Range of Soil Management Practices

P.D. Halletta, T. Baumgartlb and I.M. Youngc

a Soil-Plant Dynamics Unit, Scottish Crop Research Institute, Invergowrie, Dundee, DD2 5DA, United Kingdom
b Institute of Plant Nutrition and Soil Science, Christian-Albrechts University of Kiel, Olshausenstrasse 40, 24118 Kiel, Germany
c SIMBIOS, University of Abertay Dundee, Bell Street, Dundee, DD1 1HG, United Kingdom

Corresponding author (p.hallett{at}scri.sari.ac.uk)


   ABSTRACT
TOP
 NOTES
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 CONCLUSIONS
 REFERENCES
 
Subcritical water repellency is a poorly acknowledged physical property of soil. It refers to soil where water uptake appears to occur readily, yet is impeded to some extent by the presence of hydrophobic surface films. It was only after the recent development of a sensitive testing technique that subcritical water repellency was shown to be a common feature of many soils. It is a fundamental physical property of soil and has implications for the resistance of soil structure against disruption by wetting, bypass flow, and surface runoff. Using a technique adapted by Hallett and Young (1999), we assessed a water repellency index, R, of individual soil aggregates from a range of cultivation practices with different fertilizer inputs and depths. The parameter R is extremely powerful since it is directly proportional to the decrease in water sorptivity caused by repellency. The hypotheses tested are (i) that soil disturbance reduces R and (ii) that high levels of plant nutrients (fertilizer) will enhance R. Cultivation was found to cause a twofold decrease in R for all soils tested except one pasture treatment. Pasture soil from another site had an R value that was three times higher to a depth of 60 cm than an adjacent plowed soil. Soil aggregates were more repellent from no-till than plowed treatments. Higher levels of N added to field soil did not affect R.

Abbreviations: DRIFT, diffuse reflectance infrared fourier transform spectroscopy


   INTRODUCTION
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 CONCLUSIONS
 REFERENCES
 
LIVING MATTER IN SOIL, such as plant roots and microbes, produce extracellular polysaccharides that may enhance nutrient uptake and defend against desiccation stress (Chenu and Roberson, 1996; Hart et al., 1999). Some of these exudates form hydrophobic surface films on soil particles, particularly after physical alteration by drying or heating. Soil may also contain hydrophobic organic matter and waxes from plant leaves (Wallis and Horne, 1992). In some soils, the coverage of particles by hydrophobic surface films is so abundant that water infiltration is completely repelled (Carrillo et al., 1999). Soil exhibiting this extreme condition is not widespread, however, leading to an assumption by soil physicists that non-water repellent behavior is the norm (Wallis and Horne, 1992).

The assumption that soil is generally nonrepellent was challenged by Tillman et al. (1989). They suggested a widespread condition in soils is subcritical water repellency that occurs when hydrophobic surface coverage is less abundant. These soils are difficult to detect with conventional water repellency tests because they appear to uptake water readily. Tillman et al. (1989) overcame this problem by developing a sensitive and physically meaningful measurement of water repellency based on sorptivity. By comparing the sorptivity of water against a liquid not affected by repellency, they were able to define a repellency index that was directly proportional to the reduced infiltration rate. Further research by Wallis et al. (1991) and Hallett and Young (1999) using the technique of Tillman et al. (1989) revealed that most soils exhibit subcritical water repellency. However, given the limited amount of work conducted in this area, the implications of this finding have not been appreciated by soil scientists.

Subcritical water repellency in soil has both detrimental and beneficial impacts on the environment and agriculture. It is paramount to the hydraulic transport properties of soil and may contribute to the heterogeneity of soil structure. One direct consequence of retarded rapid wetting is enhanced structural stability of soil as the energy release rate and buildup of air pressure in pores (i.e., slaking) caused by the intrusion of water is lowered (Piccolo and Mbagwu, 1999; Caron et al., 1998), but the reduction in wetting rate also enhances surface runoff and pollutant transport through higher levels of macropore and interaggregate flow.

Soil stability and interaggregate flow properties are important to assess following tillage when the structural form of soil is predominantly discrete aggregates, particularly at or near the surface. Leeds-Harrison and Youngs (1997) devised a method for evaluating the hydraulic characteristics of individual soil aggregates using a miniature infiltration device. When they assessed the technique, some of the soils tested appeared to be hydrophobic. Hallett and Young (1999) combined their approach with the repellency technique developed by Tillman et al. (1989) in order to assess the extent of subcritical water repellency of soil aggregates amended in the laboratory with specific nutrients. It showed direct links between biological activity and subcritical water repellency of individual soil aggregates.

Biological processes and C mineralization in soil are strongly dependent on management practices (Young and Ritz, 2000). Depletion of labile C pools by intensive cultivation, for instance, reduces levels of hydrophobic material in soil (Capriel, 1997). Nutrient inputs, on the other hand, may stimulate the production of hydrophobic exudates by soil organisms (Hallett and Young, 1999; Capriel, 1997). However, information obtained using field soil to confirm these hypotheses is not available. Work in this area may provide missing physical evidence about the mechanisms responsible for different levels of soil stability, erodibility, and water transport rates that are so often observed under different management practices (Young and Ritz, 2000; Capriel, 1997). Using the approach developed by Hallett and Young (1999), we assess the effect of cultivation and fertilizer inputs on the subcritical water repellency of soil aggregates. The soils tested are from experimental plots located in the south and north of the United Kingdom and from the north of Germany.


   MATERIALS AND METHODS
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS
 DISCUSSION
 CONCLUSIONS
 REFERENCES
 
Repellency Test
The aggregate water repellency test is described in Hallett and Young (1999) and uses an infiltration device similar to Leeds-Harrison et al. (1994). An index of water repellency, R, is evaluated as suggested by Tillman et al. (1989) from the sorptivity of water, Swater, and ethanol, Sethanol, using the relationship

(1)

The constant 1.95 accounts for differences in the surface tension and viscosity between ethanol and water. By removing the influence of these liquid properties, a measurement of intrinsic sorptivity is obtained so that Swater can be compared directly with Sethanol. Ethanol readily infiltrates hydrophobic soil because of the solid–liquid contact properties. Its sorptivity therefore provides a measurement of liquid transport in soil that is not influenced by water repellency and is representative of the pore structure. A completely nonrepellent soil would have an R value of one, as defined by the physical relationship presented in Eq. [1]. Tillman et al. (1989) defined soil with R > 1.95 as subcritically water repellent. The index R is a proportional representation of how much sorptivity is reduced by water repellency. An R value of 10, for instance, would indicate that water repellency accounts for a tenfold decrease in sorptivity (i.e., the initial wetting rate).

Sorptivity is calculated from the liquid infiltration rate through a small circular area at the surface of the soil aggregate. A tube with a sponge tip in contact with the soil is connected to a liquid reservoir from which the liquid flow is recorded using a logging balance. Sorptivity, S, is measured from the steady flow of liquid, Q (m s-1), during early-time infiltration by

(2)
where b is a parameter dependent on the soil water diffusivity function (taken as 0.55; White and Sully, 1987), r is the radius of the infiltrometer tip (1.5 mm), and f is the fillable (air-filled) porosity (Leeds-Harrison and Youngs, 1997). We conducted tests at a potential of -0.2 kPa to be consistent with earlier work by Hallett and Young (1999) and to reduce macropore flow.

It has been well documented that flow through soil is affected by swelling clays and coatings on pore walls. Tillman et al. (1989) recognized that this will impose a bias on the ethanol sorptivity results but concluded that it was minor given the overall advantage of the new approach. We accept that this is one limitation of the procedure, and our work does not attempt to solve this problem as it would be a formidable task.

Studies Conducted
Soil aggregates 10 to 30 mm in diameter were collected from three experimental farms where plots have been established to assess soil management practices. In all cases, the aggregates did not exist as discrete structural units in the field so they were broken from larger clods of soil. This procedure exposes preexisting macropores that define aggregate surfaces following cultivation (Hallett et al., 1995). The location and description of the farms as well as site-specific sampling procedures are:

Kiel University, Lindhof Experimental Farm, Schleswig-Holstein, Germany
The soil is a loamy sand textured Typic Eutrocryept. The arable site is planted with winter wheat (Triticum aestivum L.) and under continuous plowing. The pasture site has remained undisturbed for at least 5 yr. Sampling was conducted in March 1999 before cultivation of the arable treatments.

Beechgrove Experimental Plots, Scottish Agricultural College, Penicuik, United Kingdom
The soil is a silty loam, classified as Macmerry Series or Oxyaquic Eutrocryrept (Ragg and Clayden, 1973). Experimental plots were established to investigate the effect of cultivation treatment (moldboard plow and no-till) and N inputs. Hallett and Young (1999) used soil collected from two plots at this site in their initial study on the subcritical water repellency of soil aggregates. Sampling was conducted in March 1999, before cultivation of the arable treatments. These plots were established in 1995 from a permanent pasture site. Since this time, the arable treatments have been planted continuously with spring barley. The adjacent fields remained as pasture. On the year of sampling, a small portion of the plowed sites was not planted and this is referred to as plow–fallow in Table 1.


View this table:
[in this window]
[in a new window]
  		Table 1. Description of the soil treatments investigated and their properties

 
Boot Field Experimental Plot, Silsoe Research Institute, Silsoe, United Kingdom
This experimental site is on heavy clay, classified as Evesham series (King, 1969) or a clayey mixed, Aquic Eutrocryept (Soil Survey Staff, 1994). The plots were established by Chamen et al. (1992) to assess a gantry tractor and used by Leeds-Harrison and Youngs (1997) to measure the hydraulic conductivity of individual soil aggregates. The field trials ceased in 1994 and since this time all of the preexisting plots have received continuous cultivation and were planted with winter wheat. As a result, our sampling was limited to one cultivated treatment and adjacent pasture and hedgerow plots. Sampling was conducted in August 1999.

The range of soil management practices investigated and basic soil properties that are important to this study are listed in Table 1. Carbon and N were measured on four replicates from a composite sample of each treatment using a continuous flow mass spectrophotometer consisting of an ANCA SL sample converter attached to a 20-20 IRMS (Europa Scientific, Crewe, UK).

Unless stated, soil was sampled from the top 10 cm at each plot. After sampling, the aggregates were dried at 40°C for 24 h. Subcritical water repellency was measured on 10 replicate samples. Fillable porosity, f, was taken as the air-filled porosity evaluated using aggregate bulk density measurements obtained with the saran resin approach (Brasher et al., 1966).


   RESULTS
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
DISCUSSION
 CONCLUSIONS
 REFERENCES
 
The cumulative infiltration of water and ethanol with time is shown for one aggregate from each of the soil management conditions at the Kiel site in Fig. 1 . Steady state infiltration occurred after 30 s and remained until testing ended after {approx}180 s for these soils and the others tested. In all cases, the relationship between infiltration and time from which Q was evaluated had r2 > 0.98.



View larger version (27K):
[in this window]
[in a new window]
  		Fig. 1. Example infiltration rates of water and ethanol for individual Kiel soil aggregates from the pasture topsoil (filled circles) and subsoil (open circles), and plowed topsoil (filled triangles) and subsoil (open triangles) plots. The data shown are for the same individual aggregate from each plot for both the water and ethanol measurements

 
There are apparent differences in water infiltration between the soil collected from plots with different management practices shown in Fig. 1. Using Eq. [1] and [2], sorptivity and the water repellence index were evaluated (Table 2). The results suggest that subcritical water repellency (R > 1.95) is widespread phenomena in these soils. Only aggregates sampled from the subsoil of the plowed plot (Kiel) exhibited nonrepellent behavior.


View this table:
[in this window]
[in a new window]
  		Table 2. Summary of water sorptivity (Swater) and ethanol sorptivity (Sethanol) and water repellency index (R) values for the different soil treatments tested

 
There is a tendency for the subcritical water repellency index to have high-end tails because the numeric value is very sensitive to hydrophobicity. For instance, the highest R value for the Beechgrove, no-till plot that had 120 kg N ha-1 added fertilizer was 15.54 compared with an average value of 5.59. To reduce the magnitude of the tails, the data was log transformed before comparison of the means using analysis of variance. Table 2 also lists the values of log-transformed data. The Anderson-Darling test was used to verify that the log-transformed data was normally distributed.

For the Kiel site, soil that was cultivated had a significantly lower level of subcritical water repellency (P < 0.001). The subsoil also exhibited lower subcritical water repellency than the topsoil (P < 0.01), with the effect being more pronounced for the plowed soil (P < 0.05). The Boot Field site also showed significant difference in subcritical water repellency between soil aggregates sampled from the range of soil management practices (P < 0.10). The pasture soil had the highest R value.

The Beechgrove soil also showed that subcritical water repellency was significantly different depending on the cultivation practice (P < 0.001). However, unlike the other sites tested, the pasture soil had a lower mean R index than the soil disturbed by plowing or no-till, and was only moderately more repellent than soil collected from the plowed site that was under fallow . The level of nitrogen did not have a significant effect on subcritical water repellency results measured on soil collected from either the plowed or no-till sites. The no-till soil, however, had a significantly higher level of sub-critical repellency than the plow soil (P < 0.01). There was no interaction between the cultivation practice and nitrogen level between the no-till and plow soil .


   DISCUSSION
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
CONCLUSIONS
 REFERENCES
 
Subcritical water repellency was found to be common feature of most of the soil aggregates tested, and its levels were different depending on soil management. In general, soil aggregates sampled from sites with more intensive cultivation showed reduced levels of subcritical water repellency. The pasture soil from the Beechgrove site, however, showed the anomalous result of having a lower R index value than some of the cultivated plots at the same site. The R index values reported here for field soils were similar to those reported by Hallett and Young (1999), who measured a smaller subset of experimental plots from the Beechgrove site. However, they were much smaller than for the soil aggregates that Hallett and Young (1999) amended with nutrients in the laboratory. Wallis et al. (1991) have published the only data of intrinsic sorptivity for a wide range of soils. They found much higher levels of R for some of the air-dried samples of the soils tested. Several soils they tested, however, had R index values <5, which correspond with our results. Their tests used soil cores rather than aggregates.

Nutrient substrate levels control the amount of biological activity that produces hydrophobic substances in soil (Hallett and Young, 1999; Wallis and Horne, 1992). Moreover, the organic matter itself may contribute to water repellency (Capriel, 1997). The differences in C and N levels shown in Table 1 depend on the incorporation and mineralization of soil residues under different management practices. Reduced levels of C caused by cultivation are typical because soil disturbance enhances C mineralization (Young and Ritz, 2000). In the Beechgrove plow site with no added N, a deficiency of N and very high C/N probably retarded the decomposition of incorporated crop residues, leading to a higher C level than the pasture site. The similar nature of the Boot Field hedgerow plot was probably a factor of low N availability and a higher proportion of lignified, woody material than the adjacent cultivated and pasture sites.

A comparison of Tables 1 and 2 reveals that links between R and nutrient substrates in the form of C and N exist in only a few extreme instances. In Fig. 2 , a plot of R against C levels demonstrates that these soil properties are poorly correlated. The only soil that shows an apparent trend is Kiel, where higher C levels corresponded with higher R . Another more tenuous trend was an overall increase in the minimum R value with increased C levels, as illustrated by the dotted line in Fig. 2.



View larger version (10K):
[in this window]
[in a new window]
  		Fig. 2. The relationship between measured C and R for soil aggregates sampled from Kiel (filled circles), Beechgrove (open circles), and Boot Field (triangles)

 
As with most interactive effects between C and other soil properties, it is not the amount of C but its form and the availability of other nutrients that probably affects subcritical water repellency (Capriel et al., 1995; Hallett and Young, 1999). The availability of N and C/N affects the degradation of substrates to produce hydrophobic substances. However, neither N nor C/N were correlated with R (Table 1 and 2).

Based on previous research findings, we expected that N levels would affect subcritical water repellency. The importance of N levels to polysaccharide production in field soils was reported by Roberson et al. (1995). They found that increases to N levels in field soil increased polysaccharide levels and soil stability. Williams and Wimpenny (1977) also reported higher exo-polysaccharide production by bacteria grown on agar plates if N levels were increased. Polysaccharides are generally hydrophilic (Piccolo and Mbagwu, 1999), but their physical alteration by drying may induce water repellency (Czarnes et al., 2000). Although this may explain the R index differences between a few of the soils tested, such as the Boot Field hedgerow and pasture plots, it does not explain the similarity between N treatments for the Beechgrove soil aggregates. One factor that may have affected our results was seasonal variability. The Beechgrove site was sampled just before primary cultivation in the spring. Burcar et al. (1994) found that water repellency levels are lowest at this time because of reduced biological processes during the winter. The effect of N levels on subcritical water repellency needs to be examined on a greater number of field sites and temporally. In an earlier study, N was found to enhance R for soil aggregates sampled at the peak of the growing season in August (Hallett and Young, 1999).

Nutrient levels and cultivation practices also affect the structure of decomposed organic matter (Oades et al., 1988). Capriel (1997) suggested an implicit link between hydrophobicity and levels of aliphatic C-H units in soil organic matter measured using diffuse reflectance infrared fourier transform spectroscopy (DRIFT). The relationship between this technique and the intrinsic sorptivity approach reported here would provide valuable fundamental information about the development of subcritical water repellency in soil. The levels of aliphatic C-H units that Capriel (1997) reports for soil under different management practices follows a similar trend to the R index values listed in Table 2.

Techniques like DRIFT (Capriel, 1997) are expensive and do not provide a quantitative measure of reduced water infiltration rates, which is how hydrophobicity manifests itself in soil. Other hydrophobicity indices, namely the Water Drop Penetration Time and Molarity of Ethanol Droplet tests, are inexpensive but only provide a qualitative measurement that is not sensitive to low levels of subcritical water repellency (Wallis et al., 1991). The test presented by Hallett and Young (1999), which measures the intrinsic sorptivity of soil aggregates, provides a physically meaningful measurement of subcritical water repellency that can be applied directly to describing early-time transport properties. It is inexpensive and easy to set up, with each test taking less than 3 min. The use of ethanol presents a bias when testing swelling soils and may dissolve organic coatings on pore walls. However, as Tillman et al. (1989) stated, this does not preclude intrinsic sorptivity as a useful index of subcritical water repellency. Our results support this argument. Nevertheless, it would be useful to investigate the effects of ethanol further or to test alternative liquids.

Applying the R index to practical soil management problems is very easy. An R index value of 5, for instance, means that there is a fivefold decrease in soil sorptivity caused by water repellency. The measurement of sorptivity in itself is an extremely important physical property of soil aggregates. By separating the transport properties of individual soil aggregates from the bulk soil, a more precise prediction of water and solute flow can be obtained using existing models (Youngs and Leeds-Harrison, 1990).

Soil management appears to have a greater effect on the subcritical water repellency of soil aggregates than on hydraulic conductivity as assessed by Leeds-Harrison and Youngs (1997). The practical implications of lower water sorptivity caused by subcritical water repellency are greater interaggregate transport and enhanced soil stability. Caron et al. (1998) found that air-pressure buildup in pores and consequently slaking was a factor of wetting rate. It is generally accepted that biological exudates in soil increase soil stability by enhancing interparticle bond energy (Chenu and Guerif, 1991; Tisdall and Oades, 1982). Biological exudates also enhance water repellency (Hallett and Young, 1999) and this factor should be taken into account when examining soil stabilization mechanisms. Despite the extensive use of soil stability measurements in research, only a small proportion of the work conducted tries to explain the processes involved. A recent study by Piccolo and Mbagwu (1999) showed that soil stability is affected considerably by the addition of hydrophobic substances. Similar work by Czarnes et al. (2000) demonstrated the combined role of enhanced interparticle bond energy and water repellency in increasing soil stability.

Our results show two- and threefold reductions in the water sorptivity of soil between sites with different management histories. The ethanol sorptivity and R index values show that subcritical water repellency has a more dominant effect on reduced water sorptivity than the pore structure. Differences in ethanol sorptivity, which provides a measurement of liquid transport in soil without an influence from water repellency, varied far less than R between the different soil management practices. To illustrate the practical significance of the results, differences between the plow and no-till sites at Beechgrove that have received 120 kg N ha-1 will be discussed. In an air-dried state, the sorptivity of water into the plow site was about 1.5 times as high as the no-till. Although a more detailed study is required to take into account the effects of pore tortuosity, this difference in infiltration rate alone could account for air-pressure buildup in pores during rapid wetting that was 1.5 times as high in the plow vs. no-till soil. As a result, the plow soil would be more likely to slake.

Based on the repellency data alone, surface run-off and interaggregate flow would be lower in the plow soil because the uptake rate of water was 50% faster. In the first few minutes of rainfall, repellency could have a drastic effect on pollutant transport and erosion.

More research is required to determine the effect of subcritical water repellency on the various processes that have been discussed. There is also a need to assess levels of subcritical water repellency on soil in its field condition, particularly after a long period of natural drying. Our samples were dried first in order to remove a potential variable between sites, simplify handling, and to maximize the time available for measuring early-time transport properties. Dry soil also simulates the extreme condition that may be expected in the top few millimeters of soil that defines the transport boundary. By testing dry soil, our results represent the potential water repellency of soil described by Dekker et al. (1998). Tests on field-moist soil would represent the actual water repellency and in wet conditions would be expected to have lower values. Nevertheless, tests by Wallis et al. (1991) on field-moist soils found that repellency was the norm rather than the exception.


   CONCLUSIONS
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 CONCLUSIONS
REFERENCES
 
Subcritical water repellency was found to be a common feature of many soil aggregates tested and was different depending on the management practices. Increased disturbance by cultivation reduced the R value for all the treatments tested except for the pasture soil at one site. No-till soil was found to have a higher R value than plowed soil. The addition of N to field soil did not appear to affect subcritical water repellency. This may be due to the spring sampling date, when levels of transient hydrophobic substances are lowest. The intrinsic sorptivity approach used for these tests was rapid, inexpensive, and sensitive to small changes in water repellency.

The effect of soil management practice on its hydraulic transport properties appears to be affected more by subcritical water repellency than differences in the pore structure, as indicated by the ethanol sorptivity results. Subcritical water repellency buffers water uptake by soil and may therefore be paramount in enhancing structural stability. It may also have the detrimental effect of causing enhanced interaggregate flow and overland runoff. With the repellency index, R can be used directly to assess how much water sorptivity is reduced. If a given management practice increases R from 2 to 5, for instance, sorptivity diminishes to 2/5 its initial value. Differences of this extent were not uncommon among soil samples from a range of management practices that were measured in this study. Ignoring subcritical water repellency, particularly in studies of aggregate stability and water transport, may be an omission of the fundamental soil property responsible for differences among management practices.

The test presented provides physically meaningful quantities that can be used in models of soil transport. The ability to obtain measurements at millimeter resolution will provide data at a scale that is not obtainable with existing techniques. As a result, predictions of both transport and spatial variability could be enhanced considerably.


   ACKNOWLEDGMENTS
 
We thank Hazel McGovern for providing the Beechgrove samples and Chris Watts (Silsoe Research Institute) for the samples from Boot Field. Jim McNicol (Biomathematics and Statistics Scotland) provided valuable assistance with the statistical analyses of data. The Scottish Agricultural College is thanked for allowing access to the Beechgrove Experimental Site. Valuable comments and suggestions from three anonymous reviewers are gratefully acknowledged.


   NOTES
TOP
 NOTES
ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 CONCLUSIONS
 REFERENCES
 
This research was supported by Grant-in-aid support from the Scottish Executive Rural Affairs Department. Travel funds for work conducted in Germany were provided by a British Council/DAAD bursary.

Received for publication January 18, 2000.


   REFERENCES
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 CONCLUSIONS
 REFERENCES
 




This article has been cited by other articles:


Home page
 Soil Sci.Home page
K. Kawamoto, P. Moldrup, T. Komatsu, L. W. de Jonge, and M. Oda
Water Repellency of Aggregate Size Fractions of a Volcanic Ash Soil
Soil Sci. Soc. Am. J., September 28, 2007; 71(6): 1658 - 1666.
[Abstract] [Full Text] [PDF]

Home page
 Vadose Zone JHome page
M. Deurer and J. Bachmann
Modeling Water Movement in Heterogeneous Water-Repellent Soil: 2. A Conceptual Numerical Simulation
Vadose Zone J., August 1, 2007; 6(3): 446 - 457.
[Abstract] [Full Text] [PDF]

Home page
 Soil Sci.Home page
H. Blanco-Canqui and R. Lal
Impacts of Long-Term Wheat Straw Management on Soil Hydraulic Properties under No-Tillage
Soil Sci. Soc. Am. J., June 8, 2007; 71(4): 1166 - 1173.
[Abstract] [Full Text] [PDF]

Home page
 Soil Sci.Home page
H. Blanco-Canqui, R. Lal, and M. J. Shipitalo
Aggregate Disintegration and Wettability for Long-Term Management Systems in the Northern Appalachians
Soil Sci. Soc. Am. J., April 5, 2007; 71(3): 759 - 765.
[Abstract] [Full Text] [PDF]

Home page
 Soil Sci.Home page
U. Buczko and O. Bens
Assessing Soil Hydrophobicity and Its Variability through the Soil Profile Using Two Different Methods
Soil Sci. Soc. Am. J., March 29, 2006; 70(3): 718 - 727.
[Abstract] [Full Text] [PDF]

Home page
 Soil Sci.Home page
R. H. Ellerbrock, H. H. Gerke, J. Bachmann, and M.-O. Goebel
Composition of Organic Matter Fractions for Explaining Wettability of Three Forest Soils
Soil Sci. Soc. Am. J., January 1, 2005; 69(1): 57 - 66.
[Abstract] [Full Text] [PDF]

Home page
 Soil Sci.Home page
P. D. Hallett, N. Nunan, J. T. Douglas, and I. M. Young
Millimeter-Scale Spatial Variability in Soil Water Sorptivity: Scale, Surface Elevation, and Subcritical Repellency Effects
Soil Sci. Soc. Am. J., March 1, 2004; 68(2): 352 - 358.
[Abstract] [Full Text] [PDF]

This Article
Right arrow Abstract Freely available
Right arrow Figures Only
Right arrow Full Text (PDF) Free
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Services
Right arrow Similar articles in this journal
Right arrow Similar articles in ISI Web of Science
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Right arrow reprints & permissions
Citing Articles
Right arrow Citing Articles via HighWire
Right arrow Citing Articles via ISI Web of Science (33)
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Hallett, P.D.
Right arrow Articles by Young, I.M.
Right arrow Search for Related Content
PubMed
Right arrow Articles by Hallett, P.D.
Right arrow Articles by Young, I.M.
GeoRef
Right arrow GeoRef Citation
Agricola
Right arrow Articles by Hallett, P.D.
Right arrow Articles by Young, I.M.

HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS
The SCI Journals Agronomy Journal Crop Science
Journal of Natural Resources
and Life Sciences Education		 Vadose Zone Journal
Journal of Plant Registrations Journal of
Environmental Quality		 The Plant Genome