bluuebunny/crossref_metadata_2025 huggingface dataset:
Soil phosphorus: its measurement, and its uptake by plants
Authors: Holford I. C. R.
Published: August 2004

Phosphorus (P) is the most important nutrient element (after nitrogen)
limiting agricultural production in most regions of the world. It is extremely
chemically reactive, and more than 170 phosphate minerals have been
identified. In all its natural forms, including organic forms, P is very
stable or insoluble, and only a very small proportion exists in the soil
solution at any one time. Plant-available P may be considered in either its
quantitative or intensive dimension. The quantity of available P is
time-specific and crop-specific, because it is the amount of P that will come
into the soil solution and be taken up by the crop during its life cycle. The
intensity of available P (availability) is most easily identified with its
concentration in the soil solution.
The soil property controlling the relationship between the solid phase P and
its concentration in solution is known as the buffering capacity. The solid
phase P involved in this relationship is only a small proportion of the total
P, and is known as labile P. It is usually measured by isotopic exchange, but
this exchangeable P component does not include the sparingly soluble compounds
that also replenish the soil solution as its concentration is depleted by
plant uptake. The buffering capacity is the ability of the soil solution to
resist a change in its P concentration as P is removed by plant uptake or
added in fertilisers or organic materials.
Buffering capacity is synonymous with sorptivity, which is a preferable term
in the context of the reactivity of P fertiliser with soil. It is usually
measured from an adsorption isotherm. By fitting a suitable equation, such as
the Langmuir, the total sorption capacity as well as the sorption strength can
be determined. Both parameters are important in understanding P availability
in soils.
Buffering capacity has a major effect on the uptake of labile P because it is
inversely related to the ease of desorption of solid phase P and its
diffusion. Available P therefore is a direct function of the quantity of
labile P and an inverse function of buffering capacity. This has been
demonstrated in plant uptake studies. Similarly, the most effective methods of
measuring available P (soil tests) are those which remove a proportion of
labile P that is inversely related to buffer capacity. Soil tests which
measure the concentration of P in solution actually measure availability
rather than available P, and their efficacy on a range of soils will depend on
the uniformity of the soils" buffer capacities.
The most effective soil test usually consists of an anionic extractant. Acidic
lactate or fluoride have been found most effective in New South Wales, on a
wide range of soils, except calcareous soils which neutralise the acidic
component (usually hydrochloric or acetic acid) of the extractant. Sodium
bicarbonate (pH 8 · 5) has been found effective on calcareous soils and
is widely used throughout the world. It has proved unreliable on NSW soils,
and may need more thorough evaluation on non-calcareous soils in other parts
of Australia.
Initial soil pH affects the pH at which nitrification ceases due to self-induced acidification of microbial microsites
Authors: Strong D. T. , Sale P. W. G. , Helyar K. R.
Published: August 2004

The existence of microsites of low pH around active colonies of nitrifying
soil bacteria has previously been suggested but has been difficult to verify.
A study was undertaken to examine whether observed decreases in bulk soil pH
that occur during nitrification are in accordance with the theory of acidified
nitrification microsites. A red earth soil (sieved <2 mm) was retained at a
pH of 5·3 or amended with KHCO3 to achieve a pH
of 6·3. Ammonium
[(NH4)2SO4]
was added to the soils and they were incubated for 35 days. In both soils the
pH dropped rapidly and severely limited further nitrification. The soil with
the higher initial pH experienced limitations to nitrification at a pH which
was 0·2 units higher than that of the soil with the lower initial pH.
The explanation for this result is in terms of acidified nitrification
microsites. It is suggested that an active nitrifying colony may lower the pH
within its immediate vicinity to a critical pH at which nitrification almost
ceases. This critical pH achieved at the nitrification microsite is probably
unrelated to the initial pH of the soil, but the pH of the soil matrix which
is distant from the immediate influence of the nitrification microsite would
remain at a pH closer to that of the soil initially. This less acidified
region of the soil matrix would have an overriding influence on the measured
pH of the bulk soil and account for the discrepancy between the measured pH of
the two soils at the end of the incubation. These data provide further
evidence that acidified nitrification microsites exist in soil, and that the
measured soil pH is a poor estimate of the pH experienced by the microbial
biomass.
A technique for the non-destructive measurement of nitrate in small soil volumes
Authors: Strong D. T. , Sale P. W. G. , Helyar K. R.
Published: August 2004

Two simple techniques designed to measure nitrate
(NO3-N) non-destructively in small undisturbed soil
samples are described. A small water-filled ‘receptor’ is placed
in contact with a small soil volume (~1·7 cm3)
enabling the concentration of NO3-N in the interstitial
water of the receptor to approach the concentration of
NO3-N in the interstitial water of the soil sample by
the process of diffusion. The NO3-N concentration in the
receptor water is then measured, and from this, the
NO3-N concentration in the soil is estimated.
The receptor used in the first technique was a disc of agar (diameter 8 mm and
thickness 3 mm). This was placed on the soil volumes and allowed to
equilibrate for 22 h before NO3-N in the soil and in the
agar were determined. The regression of actual soil
NO3-N against estimated soil NO3-N
using this receptor yielded an r2
value of 0·99 and a slope coefficient of 1·01. The main
disadvantage of this technique was that it was necessary to bring the soil to
a water potential close to saturation before the agar discs were applied. If
the soil had even a slight negative water potential (–10 kPa), water
would drain out of the agar rendering it useless and would also alter the soil
water potential in the process. For this reason, this technique is only
recommended for use with soils which are close to saturation.
The second technique used ceramic discs as the receptors to overcome the
deficiencies of the agar discs. The ceramic discs had dimensions similar to
the agar discs and had a gravimetric water content of 0·25 g/g at a
water potential of –30 kPa. They were equilibrated with the soil for a
period of 10 days. The regressions of actual soil NO3-N
against estimated soil NO3-N had
r2 values >0·99, and the
slope coefficients ranged between 1·08 and 1·11. It was
concluded that this technique is a useful tool for the non-destructive
measurement of NO3-N in small undisturbed volumes of
soil.
Phosphorus requirements of Australian native plants
Authors: Handreck Kevin A.
Published: August 2004

The phosphorus (P) requirements of Australian plants are reviewed. Many
Australian plants have highly developed abilities for acquiring and
conservatively using P. This is seen as an evolutionary response to the
combined environmental pressures of fire, soil P levels that are in the lower
part of the range for world soils, and low and eratic rainfall. In natural
Australian ecosystems, more than 50% of the P in the A horizon is in
organic combination. Organic matter is the main source for the growth of
perennial plants, so the only successful assessments of
‘available’ P measure labile organic P and microbial P. However,
the inorganic P of ashbeds is essential to the rapid establishment of fire
ephemerals and tree seedlings in natural ecosystems. Almost all Australian
plants develop associations with mycorrhizal fungi, or produce hairy roots, as
ways of increasing P uptake. Highly developed abilities to redistribute P from
ageing to young tissues enable Australian plants to have a low P requirement
per unit of biomass production. This also results in low P losses in sawlogs
from natural forests, but not necessarily from short-rotation plantations. The
special role of P in the ecology and conservation of heathlands is reviewed.
Finally, an overview is given of the P requirements of Australian plants being
grown in soil-less media in nurseries.
An examination of the end-over-end shaking technique for measuring soil dispersion
Authors: So H. B. , Cook G. D. , Raine S. R.
Published: August 2004

The end-over-end shaking technique has been widely used to provide a measure
of soil dispersibility. However, results are dependent on the specific
methodology employed. This paper investigates the effect of various physical
parameters on the dispersion produced using an end-over-end shaking technique.
Significant (P < 0·05) increases in the
percentages of clay (D2) and
silt+clay (D20) particles
dispersed as a proportion of the total soil weight were observed with
increasing period of shaking, suspension concentration, container size, and
air-gap above the suspension. However, differences due to suspension
temperature and soil texture were either relatively minor or insignificant
(P > 0·05). To enable better comparison of
results from different workers, the following methodology for end-over-end
shaking studies is proposed as a standard. The soil sample should be air-dried
and crushed to pass through a 2-mm sieve. The air-dried equivalent of 50 g
oven-dried soil should then be immersed in 1 L double-deionised water at
20°C within a 1·425-L cylinder (70 mm internal diameter) and shaken
end-over-end at 20 rpm for 30 min before measuring the amount of dispersed
<2 and <20 µm material produced. The amount of dispersed material
should be expressed as a proportion of the total soil material.
Assessment of erosion rates from microphyte-dominated calcareous soils under rain-impacted flow
Authors: Eldridge D. J. , Kinnell P. I. A.
Published: August 2004

Intact soil monoliths with surfaces of varying microphytic crust cover were
collected from a calcareous earth soil in a semi-arid belah–rosewood
woodland near Wentworth in south-western New South Wales. Monoliths were
tested for their susceptibility to erosion by rain-impacted flow using a
laboratory rainfall simulator. The erosive stress applied to each surface was
controlled by varying the flow depth between 4 and 8 mm whilst maintaining a
flow velocity of 25 mm/s using 2·7 mm raindrops falling 11·2
m at average rainfall intensities of 65 mm/h. Increasing the cover of
microphytic crusts on the surface resulted in a significant
(P = 0·001) reduction in sediment
concentration. A linear model incorporating percentage cover and distribution
of cover accounted for 46% of the variance in soil erosion. A
significant relationship was also found between the coarse fraction
(>0·053 mm) and crust cover (P =
0·012) at the 4-mm depth. Management practices such as overgrazing,
trampling, and fire, which reduce the cover of crusts in this landscape, will
lead to increased erosion hazard.
Earthworms in some Tasmanian forest soils in relation to bioturbation and soil texture profile
Authors: Laffan M. D. , Kingston T. J.
Published: August 2004

Soil properties and earthworm population density were examined for 5 forest
soils derived from Silurian-Devonian sandstones (Mathinna Beds) in
north-eastern Tasmania. The soils occur along gradients of altitude, rainfall,
and forest type; they include 2 with texture-contrast and 3 with gradational
soil profile types. The density and biomass of the most abundant earthworm
species Megascolex montisarthuri, and of all earthworm
species combined, were found to be greater in gradational than in
texture-contrast soils. A greater proportion of the earthworms in gradational
soils than in texture-contrast soils was found to occur at soil depths
exceeding 10 cm. The contrast was most pronounced between the 2
texture-contrast soils and the single gradational soil that occur under dry
eucalypt forest. This paper explores the hypothesis that bioturbation of
surface and subsurface layers by earthworms is an important mixing process
that in gradational soils outweighs the counter tendency for soil particles to
sort and thus form texture-contrast profiles.
Soil - landscape relationships of downlands soils formed from loess, eastern South Island, New Zealand
Authors: Webb T. H. , Burgham S. J.
Published: August 2004

The Timaru and Claremont soil series occupy >145 000 ha of loess-mantled
downlands of the South Island. The soils are mapped in large map delineations
and the accompanying soil reports provide very generalised descriptions and
definitions of the units. Almost no information is recorded on the nature and
causes of soil variability. In this study soil variability is described along
transects at 12 locations. The sites selected encompass a range of aspect
(sunny and shady), topography (easy rolling to strongly rolling terrain), and
land use (non-ploughed, pastoral, and mixed cropping).
The definitions of the Timaru and Claremont series are refined and the
variability in soil morphology is related to landscape features. Morphological
data from the transects are collated into generalised soil–landscape
models. Similar arrays of soils occur within the Timaru and Claremont
soil–landscape models. The models vary mainly in the occurrence and
depth to reducing conditions. The soil–landscape models provide a
framework within which to derive soil attribute values for use in predictive
models and land-use interpretations, and provide a baseline from which future
studies may assess the impacts of land-use practices.
In both soil series, the thickness of topsoils, depth to reducing conditions,
and depth to fragipans are greatest on footslopes and generally decrease to
shoulderslopes. Penetration resistance is lowest on footslopes and increases
to shoulderslopes. In cultivated land, footslope sites have markedly
over-thickened topsoils. Relocation of topsoil material from upper to lower
slopes is attributed mainly to the effects of cultivation, either directly,
through mechanical movement of soil material during cultivation operations, or
indirectly, through the promotion of soil erosion. Variations in depth of soil
materials are expected to have attendant affects on potential productivity.
Charge fingerprints of forest organic horizons from north-eastern USA
Authors: Ross Donald S. , Bartlett Richmond J.
Published: August 2004

The charge fingerprint procedure was used to characterise the exchange
properties of high- organic forest soils from the north-eastern USA.
Twenty-six Oa or A horizon samples were obtained from active research sites to
provide samples with a range in carbon from 15·1 to 49·4%
and pH (in 1 mM CaCl2) from 2·8 to 4·2.
Fingerprints were similar to those developed for other variably charged soils
except that significant quantities of exchangeable H+
were found and no appreciable anion exchange capacity was measured. The
magnitude of the ‘base’ cation capacity
(CECB) varied linearly with pH, averaging >50%
change per unit pH change. A good estimate of the CECB
was obtained from the sum of cations removed by a single extraction with
1·0 М choline chloride (slope 1·03,
r2 = 0·91).
Variations in exchangeable Al3+ or
H+ with pH were related to the quantity found in
untreated samples, probably because of the close association between
exchangeable and organically complexed forms. The total CEC was closely
related to the sum of cations removed by 0·1 M
BaCl2 (slope 1·05,
r2 = 0·96). Although
low ionic strength may be difficult to maintain in low pH samples, the
fingerprint method appears to allow precise interpolation of the organic
soils’ exchange capacity at field pH.
Magnesium in tropical and subtropical soils from north-eastern Australia. II. Response by glasshouse-grown maize to applied magnesium
Authors: Hailes K. J. , Aitken R. L. , Menzies N. W.
Published: August 2004

A glasshouse trial, in which maize (Zea mays L. cv.
Pioneer 3270) was grown in 35 north-eastern Australian soils of low magnesium
(Mg) status, was undertaken to study the response to applied Mg. Of the soils
studied, 20 were strongly acidic (pH1:5 soil : water
<5·4), and in these soils the response to Mg was studied in both the
presence and absence of lime. Magnesium application significantly
(P < 0·05) increased dry matter yield in 10
soils, all of which were strongly acidic. However, significant Mg responses
were recorded in 6 soils in the presence of lime, indicating that, in many
situations, liming strategies may need to include consideration of Mg
nutrition.
Critical soil test values for 90% relative yield were 0·21
cmol(+)/kg of exchangeable Mg or 7% Mg saturation, whilst the
critical (90% yield) plant tissue Mg concentration (whole shoots) was
0·15%.
Fate of nitrogen in pig slurry applied to a New Zealand pasture soil
Authors: Carey P. L. , Rate A. W. , Cameron K. C.
Published: August 2004

A 2-year lysimeter study was conducted to determine the fate of nitrogen in
pig slurry applied to a moderately fertile, semi-free-draining pasture soil in
the Canterbury Plains of New Zealand. Pig slurry was applied annually for 2
years in autumn, at 3 rates of 0, 200, and 400 kg N/ha to 12 large soil
lysimeters (4 at each rate), 800 mm in diameter by 1200 mm deep. Slurry
applied in Year 1 was labelled with 15N and a mass
balance obtained at the end of the experiment.
The mass balance showed that over the 2 years following application of
15N-labelled slurry, 8–19% was lost in the
leachate, 20% was removed in the cut pasture, 15–26% was
lost via volatilisation, 14–18% remained in the roots and soil,
and approximately 30% was lost by denitrification. The high
denitrification loss was attributed to (i) a large soil
concentration of nitrate supplied from nitrification of the ammonium-N in the
slurry; (ii) a readily oxidisable source of carbon
supplied in the slurry; and (iii) transient anaerobic
conditions produced by textural discontinuities and impeding layers within the
soil profile. The fate of applied nitrogen between years was affected by the
pattern of water inputs (rainfall and irrigation) and the resulting effect on
drainage.
Concentrations of inorganic nitrogen in the leachate from the 200 kg
N/ha·year treatment were found to be consistently below 25 mg
N/L, but those from the 400 kg N/ha·year treatment were
considerably higher (c. 65 mg N/L) and persisted for
a prolonged period. The latter N concentration represented a significant loss
of nitrogen over the study period and may be of environmental concern.
Soil science: raising the profile
Authors: White Robert E.
Published: August 2004

The low public profile of soil science and its practitioners nationally and
internationally is noted against a widespread general concern about food
supplies and our collective ability to sustain soil resources for agriculture.
The historical development of soil science as a recognised discipline is
traced from the early Russian pedological work to the current proliferation of
taxonomic approaches for codifying soil information; from the application of
the basic sciences to measuring soil properties and understanding soil
processes; and from traditional soil survey to modern `information
technology" approaches to extending soil information in an easily
accessible form to a variety of end-users. The provision of soil information
systems and management models at appropriate scales, and the development of
site-specific farming systems, are some of the key areas for contributions
from soil scientists in the future. This opportunity exists in urban and rural
areas. To grasp these opportunities, soil scientists will need to be more
proactive in the scientific community, seeking to interact where possible with
ecologists, engineers, economists, and social scientists to enhance the
visibility and perceived importance of soil science across traditional
boundaries. To raise further their public pro¯le, they will also need to
make a success of their professional accreditation scheme.
The fate of nitrogen fertilisers added to red gradational soils at Batlow, New South Wales, and its implications with respect to soil acidity
Authors: Little I. P.
Published: August 2004

Red gradational soils at Batlow, in New South Wales, which are used for apple
growing, have acid subsoils with exchangeable aluminium (Al) frequently in
excess of exchangeable calcium (Ca). There is often inadequate Ca in the fruit
cortex of post-harvest apples to maintain good fruit quality and this can lead
to losses in cool-store. It is possible that Al in these acid subsoils has
interfered with Ca uptake by the trees. The excessive use of nitrogenous
fertilisers leads to soil acidity, and it was thought likely that this was
exacerbating the subsoil acidity common in the district.
In October 1992, soil analysis detected considerable ammonium in the surface
0·3 m at orchard sites at Batlow monitored for mineral nitrogen (N).
This probably came from heavy spring dressings of fertiliser. One site
examined in detail showed that about half of the ammonium had disappeared by
January 1993, but a large nitrate envelope appeared with a peak at 0·6
m which in turn disappeared by April that year. This establishes that heavy
applications of ammonium are nitrified, leached into the subsoil, and lost.
Under such a high N regime, orchard soil profiles should be more acid than
adjacent forest soils. However, it was found that the acidity of the surface
soil was less, and the exchangeable Ca greater in the orchard soils, compared
with soil profiles in the adjacent eucalypt forest, although amelioration of
the subsoils had not occurred.
Samples taken from representative sites at Batlow, at the 0–0·1,
0·1–0·2, and 0·3–0·4 m depths, were
dosed with ammonium sulfate and leached with water in the laboratory for 23
days in a free-draining environment. Nitrate and ammonium were determined in
the leachates. At the end of the experiment, the pH and exchangeable Ca, Mg,
and Mn were determined in the leached samples. Only the neutral surface soils
were able to nitrify ammonium effectively and nitrification was positively
correlated with pH, and with exchangeable Ca and Mg.
From this it is argued that the acidity produced by the addition of ammonium
sulfate or urea will be nitrified in the surface but the acidity produced will
be neutralised, provided it is accompanied by an adequate dressing of lime.
Ammonium tends to remain in the surface soil, but if leached, it will not be
nitrified in the subsoil. Nitrate leached into the subsoil will not be
acid-forming but, if denitrified, may help to reduce acidity.
For this work, the soil pH was measured in 1 KCl. So that readers can refer
this to the pH in 0·01 CaCl2, a relationship was
established between the two measures.
Sorption and degradation of phorate as influenced by soil depth
Authors: Bolan N. S. , Baskaran S.
Published: August 2004

The sorption and degradation of a non-ionic insecticide (phorate) were
examined using 14 soil samples collected at different depths from 2 soil types
(Tokomaru and Egmont) which differed in their organic matter and clay
mineralogy. Organic carbon and biological activity, as measured by
substrate-induced respiration (SIR), decreased with soil depth. Sorption of
phorate, as measured by the distribution coefficients
(Kd), was greater for the Egmont
than for the Tokomaru soil and decreased with depth for both soils. The
difference in Kd values between
the soils and soil depths was related mainly to the difference in the amount
of organic carbon. The rate of degradation, as measured by the half-life
(t1/2), decreased with soil
depth except for the last 2 depths. The initial decrease in the rate of
degradation was attributed to the decrease in the biological activity with
depth. In the last 2 depths, since the sorption was low, most of the phorate
tended to remain in soil solution, resulting in a slight increase in the rate
of degradation. These results suggest that the changes in soil organic carbon
with depth may be a reasonable indicator of microbial activity and subsequent
changes in the rate of pesticide degradation as a function of soil depth.
Groundwater flow modelling to assist dryland salinity management of a coastal plain of southern Australia
Authors: Pavelic Paul , Narayan Kumar A. , Dillon Peter J.
Published: August 2004

Groundwater flow modelling has been undertaken for an area of 10 500 ha within
the regional unconfined aquifer system of a coastal plain of southern
Australia, in the vicinity of the town of Cooke Plains, to predict the impact
of various land management options (including recharge reduction and discharge
enhancement) on the extent of land salinisation caused by shallow saline
watertables. The model was calibrated against field data collected over 6
years. Sensitivity analysis was performed to assess the influence of mesh
size, boundary conditions, and aquifer parameters, and particularly rates of
recharge and evaporative discharge, on groundwater levels. These were varied
until the model was shown to be capable of simulating seasonal trends and
regional and local flow patterns. The model was then used to predict the
impact of the management options on groundwater levels.
The results showed that continuing current annual crop–pasture rotations
will result in watertable rises of approximately 0·2 m in 20 years
(significant in this setting), with a further 50 ha of land salinised. A
reduction in the rates of groundwater recharge through the establishment of
high water-use perennial pastures (e.g. lucerne) showed the most promise for
controlling groundwater levels. For example, a reduction in recharge by
90% would result in watertable declines of 0·6–1·0
m within 5–10 years, with the return to productivity of 180 ha of saline
land. Small-scale (say <100 ha) efforts to reduce recharge were found to
have no significant impact on groundwater levels. Enhanced groundwater
discharge such as pumping from a windmill was found to be non-viable due to
the relatively high aquifer transmissivity and specific yield.
The modelling approach has enabled a relatively small area within a regional
aquifer system to be modelled for a finite time (20 years) and has shown that
extension of the boundaries of the model would not have altered the predicted
outcomes. Furthermore, the analysis of sensitivity to cell size in an
undulating landscape where net recharge areas can become net discharge areas
with only small increases in groundwater level is novel, and has helped to
build confidence in the model.
Modelling has demonstrated that dryland salinisation can be controlled by
reducing groundwater recharge over substantial tracts of land, and is not
dependent on recharge reduction over an extensive area upgradient, at least
over the next 20 years.
Has biotechnology a role in soil science?
Authors: Lynch J. M.
Published: August 2004

Biotechnology is discussed in terms of its potential to improve crop
productivity and protect the environment. The topics covered include soil
stabilisation, dinitrogen fixation, plant growth enhancement, biocontrol,
bioremediation, and sustainability. It seems that soil science and
biotechnology are totally interactive and both disciplines will advance where
it is recognised that interdisciplinary studies are most valuable. Many
advances in medicine and pharmacology are based on developments in soil
science, such as the discovery of streptomycin from soil-borne actinomycetes.
The soil biota should produce much scope yet for further discoveries, and
there seems to be a place for soil science courses in biotechnological,
environmental health, and medical education.
Are rural land practices in the Murray-Darling Basin a threat to the environment?
Authors: Blackmore Don , Connell Daniel
Published: August 2004

Over the last 150 years Australia has gained great economic rewards from the
use of the natural resources of the Murray-Darling Basin. However, many of the
methods used to gain those benefits are now seen as unsustainable. To maintain
the region’s productivity in the future, a different approach to
managing its natural resources is needed. This paper explains the economic and
environmental importance of the Basin, describes the degradation that has
occurred, and summarises the efforts being made to achieve sustainable
management of the region.
The performance and radiation exposure of some neutron probes in measuring the water content of the topsoil layer
Authors: Arslan A. , Razzouk A. K. , Al-Ain F.
Published: August 2004

The use of neutron scattering technique for determining the soil surface water
content is not popular due to the radiation escaping from the soil surface and
the large errors in measurement. To compare the radiation exposure and the
performance of different techniques statistically, 3 sites were selected. Five
different neutron probe models and different adaptors were used with the depth
probes. Exposure to neutrons and γ radiations, at various distances from
the probes, were determined. In situ calibration curves
were determined using different models of depth probes with a Solo surface
reflector block, CPN surface adaptor, and different numbers of plastic Teflon
parallelepiped, as well as surface Troxler 3401-B probes. Depth neutron probe
readings increased with increasing number of Teflon plastic blocks deposited
on the soil surface. The intercept of the straight line regression analysis of
CR (count ratio, surface count over standard count) u. percentage water
content on a volume basis decreased with increasing number of blocks deposited
on the soil surface at all sites. The determination coefficient values of any
depth probe with a Solo surface reflector or a block of 4·8 cm
thickness were higher than those of a Troxler 3401-B surface probe or CPN 503
depth probe with its surface adaptor. The least exposure to radiation was with
a depth probe with surface reflectors. This study proves the possibility of
measuring the moisture content of the soil surface by using a depth neutron
probe with a block laid on the surface, without danger of receiving the
threshold dose of radiation.
Morphology and behaviour of greigite from a Holocene sediment in Eastern Australia
Authors: Bush Richard T. , Sullivan Leigh A.
Published: August 2004

Greigite (FeS1·34) was identified in the black
magnetic fraction of a freeze-dried unoxidised estuarine sediment by X-ray
diffraction and scanning electron microscopy with quantitative energy
dispersive X-ray analysis. The greigite crystals were tabular, unlike the
cubic morphology described in the literature, and ranged in size up to 1
µm wide and 0·2 µm thick. The stability of greigite was
monitored by changes in peak intensities in X-ray diffractograms for a sample
of greigite after exposure to a range of oxidising conditions. Moist greigite
(with an approximate moisture content of 0·35 g/g) oxidised within
hours under ambient conditions at 25°C and within minutes at 88°C.
However, greigite was relatively stable if kept air-dry. The results indicate
standard sample-handling and oven-drying procedures presently used for
sulfidic sediments to minimise oxidation actually enhance greigite oxidation
and suggest greigite may have an important role in the acidification of these
sediments in the field.
Development of an improved Vertisol stability test for SOILpak
Authors: Field Damien J. , McKenzie David C. , Koppi Anthony J.
Published: August 2004

The stability in water of soil from 3 contrasting Vertisols was measured using5 tests. Two end-over-end shaking procedures, the Loveday & Pyledispersion test, and the relatively rapid SOILpak procedure of Daniells & Larsen were assessed. The latter method has been modified to deal with severaldeficiencies such as its lack of score subdivisions; the new procedure isreferred to as the ‘aggregate stability in water’ (ASWAT) test. Wecorrelated data from all the tests under consideration to provide definitionsof the ‘critical’ point at which dispersion becomes a problem forland managers. Three soil management zones have been defined provisionallyusing data from the ASWAT and end-over-end ‘aggregate stability’tests. The scheme allows appropriate surface soil management strategies to bepredicted using the ASWAT test. The relationship between data from the ASWATtest and exchangeable sodium percentage indicated that factors other thanexchangeable sodium strongly influence dispersibility of the samples underconsideration.
The accession of chloride to the western half of the Australian continent
Authors: Keywood M. D. , Chivas A. R. , Fifield L. K. , Cresswell R. G. , Ayers G. P.
Published: August 2004

Chloride concentrations in bulk precipitation, collected from 18 sites in
remote areas of Australia over 2 years, exhibit a dependence on distance from
the coast that is well described by the sum of 2 exponentials. Various
processes are discussed in terms of their contribution to the
‘fast’ and ‘slow’ components of this relationship. A
map of chloride accession to the western and central areas of the Australian
continent is constructed. Maximum deposition occurs at coastal localities
(60–70 kg/ha), decreasing to <1 kg/ha in the interior of the
continent. Chloride deposition shows a decrease from south (70 kg/ha) to
north (<5 kg/ha) of the continent, re˚ecting the greater
importance of the subpolar marine airmasses in the supply of ionic species to
the Australian continent, and the influence of the continental airmass, low in
chloride, on salt deposition in northern Australia.
Computer modelling of the effect of revegetation strategies on salinity in the western wheatbelt of Western Australia 2.
Authors: Clarke C. J. , Mauger G. W. , Bell R. W. , Hobbs R. J.
Published: August 2004

This is the second of 2 papers to describe computer modelling of the effect of
revegetation strategies on land and stream salinity in the wheatbelt of
Western Australia and deals with the impact that the higher hydraulic
conductivity within major fault zones has on the effectiveness of revegetation
treatments. Increasing the hydraulic conductivity by factors of 5 or 10
increases saline seepage by about 140% or 160%, respectively,
for most treatments. For a treatment to have the same effect with the fault as
without it requires an increase of 50% in the number of tree rows. This
has major consequences for the management of water resources, as ignoring
faults seriously underestimates the problem.
Increasing the hydraulic conductivity has only a fairly small effect on the
area of salinised land, an increase of up to 4% of the cleared area.
However, tree-row spacing may need to be reduced by two-thirds to have the
same effect as would be expected without the fault. Thus, although the change
in salt land area is relatively small, the fault still has a big impact on the
density of treatments necessary to get the same effect, which has some
consequences for land managers.
Mobility of metsulfuron-methyl in tropical soils
Authors: Ismail B. S. , Kalithasan K.
Published: August 2004

The mobility of metsulfuron-methyl in 5 soil series with different organic
contents was determined in a greenhouse as well as under natural conditions.
In these studies, the movement and biological activity of metsulfuron-methyl
were determined by the bioassay method using long bean as a bioassay species.
Bioactivity and movement of the herbicide down the soil profile were inversely
related to the organic matter content of the soil. Phytotoxic levels of
metsulfuron-methyl were restricted to the 10-cm depth of the column containing
Selangor Series soil except when it received 40 mL of water daily (depth,
10–15 cm). In Munchung Series, the phytotoxic level was also mainly in
the 5–10 cm layer. However, when the column received 40 mL daily or
every 4 days, the residue was detected in 15–20 cm and 10–15 cm
zones, respectively. The phytotoxic level moved downward to the 20–25 cm
layer both in Sogomana and Holyrood Series when 40 mL of water was given
daily. A phytotoxic level of metsulfuron herbicide was detected in the
20–25 cm layer when the soil column containing Serdang Series was
leached with 40 mL of water every 4 days or with 20 mL daily; the phytotoxic
level was detected at a depth of 25–30 cm when this soil was watered
daily with 40 mL. The downward movement of metsulfuron under natural
conditions showed a pattern similar to that found under simulated conditions.
Phytotoxic effects of the residue could be detected in the 25–30 cm and
15–20 cm zone of Serdang and Holyrood Series, respectively, after
exposure to 20 days of rainfall (total 111·9 mm). Phytotoxic residue in
both Sogomana and Munchung Series soil was detected in the 10–15 cm
layer, and in the 5–10 cm layer for Selangor Series soil, after exposure
to 20 days of rainfall. After exposure to 40 days of rainfall (total
152·8 mm) under natural conditions, the residue could be detected in
the 15–20 cm layer of Selangor Series. The phytotoxic level moved deeper
in soil with low organic matter after exposure to 40 days of rainfall. Fresh
weight reduction was greater in the 20–30 cm layer in Serdang Series
than in the top layer.
Water balance in swelling materials: some comments
Authors: Smiles D. E.
Published: August 2004

Materials ranging from wet tailings in retention ponds through potentially
acid sulfate sediments in humid marine environments to clay soils in semi-arid
climates shrink and swell with change in water content. This paper discusses
the formulation and determination of material balance in such swelling and
cracking materials. Significant errors and their likely magnitudes are
identified when these estimates are based in physical space, as opposed to
material space. Ways in which this problem might be dealt with are discussed.
The role of the geometry and frequency of rectangular rills in the relationship between sediment concentration and stream power
Authors: Fentie B. , Rose C. W. , Coughlan K. J. , Ciesiolka C. A. A.
Published: August 2004

We examined, both experimentally and theoretically, whether rilling results in
higher soil erosion than would have occurred without rilling. The possibility
of rilling occurs when overland flow-driven erosion processes are dominant
over erosion due to raindrop impact, and that is the situation assumed in this
paper. Stream power (or a quantity related to stream power such as shear
stress) is commonly used to describe the driving variable in flow-driven
erosion.
Five flume experiments were designed to investigate the relationship between
stream power and sediment concentration and how this relationship is affected
by the ratio of width to depth of flow (r), and the
frequency or number of rills per metre width (N) of
rectangular rills. This paper presents the results of these experiments and
uses a physically based soil erosion theory to show that the results of the 5
flume experiments are in accord with this theory. This theory is used to
investigate the effect of all possible rectangular rill geometries and
frequencies on the maximum possible sediment concentration, i.e. the sediment
concentration at the transport limit, by developing general relationships for
the influence of r and N on
sediment concentration.
It is shown that increased stream power, which can be due to rilling, does not
necessarily result in higher sediment concentration.
Rainfall erosivity and its estimation for Australia's tropics
Authors: Yu B.
Published: August 2004

Pluviograph data at 6-min intervals for 41 sites in the tropics of Australia
were used to compute the rainfall and runoff factor
(R-factor) for the Revised Universal Soil Loss Equation
(RUSLE), and a daily rainfall erosivity model was validated for these tropical
sites. Mean annual rainfall varies from about 300 mm at Jervois (015602) to
about 4000 at Tully (032042). The corresponding R-factor
ranges from 1080 to 33500 MJ·mm/(ha ·h·year). For
these tropical sites, both rainfall and rainfall erosivity are highly seasonal
with a single peak in February mostly. Summer months (November–April)
typically contribute about 80% of annual rainfall and about 90%
of the R-factor. The daily erosivity model performed
better for the tropical sites with a marked wet season in summer in comparison
to model performance in temperate regions of Australia where peak rainfall and
peak rainfall erosivity may occur in different seasons. A set of regional
parameters depending on seasonal rainfall was developed so that the
R-factor and its seasonal distribution can be estimated
for sites without pluviograph data. The prediction error using the regional
parameter values is about 20% for the R-factor
and 1% for its monthly distribution for these tropical sites.
Mineralisation of soil organic nitrogen and microbial respiration after simulated summer rainfall events in an agricultural soil
Authors: Murphy D. V. , Sparling G. P. , Fillery I. R. P. , McNeill A. M. , Braunberger P.
Published: August 2004

Simulated rainfall events were applied during the summer fallow period to a
Western Australian agricultural soil, a loamy sand, under continuous wheat and
after the second pasture phase of a 2 pasture : 1 wheat (2P : 1W) rotation.
The aims of this study were to determine the change in microbial activity,
amount of net and gross nitrogen (N) mineralised, and inorganic N produced
after dry soil was re-wet during summer rainfall. Three irrigation treatments
were applied: (i) control soils received no water, (ii) the single wet
treatment received 45 mm of water on day 0 and was allowed to dry, and (iii)
the multiple wet treatment received 45 mm of water on day 0 plus further
applications of 5 mm on days 3 and 8. The CO2 production
and N mineralisation were measured in the surface 10 cm of soil for a period
of 14 days after initial irrigation. Net N mineralisation was measured from
in situ incubation of soil cores and gross N
mineralisation by 15N isotopic dilution. The
CO2 production was measured by infrared gas analysis of
air samples taken from a closed headspace above the soil. A large flush in
CO2 production and gross N mineralisation occurred
immediately after rewetting the dry soil. This response was short-lived and
rates of CO2 production and gross N mineralisation
declined rapidly after 2 days. After irrigation on day 0,
CO2 production was twice as large and gross N
mineralisation was slightly larger in the 2P : 1W soil than continuous wheat.
Gross N mineralisation and CO2 production were not
significantly different in the multiple and single wet treatments after the
re-wet on day 3, but an additional flush in activity occurred in the multiple
wet treatment after the re-wet on day 8. The patterns of gross N
mineralisation and CO2 production corresponded to
changes in the soil water content, especially in the surface 2·5 cm of
soil. Net and gross N mineralised and gross N immobilised over the 14-day
period after the initial re-wet were greater in the multiple wet compared with
the single wet treatments under both wheat and 2P : 1W. However, gross N
mineralisation was approximately 4-fold greater than net N mineralisation
under wheat and 15-fold greater under 2P : 1W. The majority of gross N
mineralised after simulated summer rainfall was immobilised which resulted in
an increase in inorganic N within the soil profile (0-50 cm) during opening
winter rains.
Stratification of microbial biomass C and N and gross N mineralisation with soil depth in two contrasting Western Australian agricultural soils
Authors: Murphy D. V. , Sparling G. P. , Fillery I. R. P.
Published: August 2004

The distribution of microbial biomass C and N and the decline in gross N
mineralisation and NH4+
consumption with soil depth was investigated in 2 soils with different soil
texture and land use. Soils were from an annual pasture on a loamy sand and
from a sandy clay loam previously cropped with wheat. Intact soil cores were
collected from the surface 0–10 cm in steel tubes and were sampled in
2·5 cm layers. Disturbed soil down to 50 cm was collected in 10 cm
sections using a sand auger. Microbial biomass was estimated by chloroform
fumigation and 0·5 M K2SO4
extraction. Microbial biomass C was determined from the flush in
ninhydrin-positive compounds, and microbial biomass N from the flush in total
soluble N after
K2S2O8
oxidation. Gross N mineralisation and
NH4+ consumption were estimated by
15N isotopic dilution using
15NH3 gas injection to label the
soil 14NH4+
pool with 15N. The pattern of distribution of the
microbial biomass and the rate of N transformations were similar for both
soils. There was a rapid decline in microbial biomass C and N and gross N
mineralisation with soil depth. Approximately 55% of the microbial
biomass, 70–88% of gross N mineralisation, and
46–57% of NH4+
consumption was in the surface 0–10 cm in both soils. There was also a
stratification of microbial biomass and gross N mineralisation within the
0–10 cm layer of intact soil cores. It was estimated that one-quarter of
the total microbial biomass and at least one-half of the total gross N
mineralisation within the soil profiles (0–50 cm) was located in the
surface 2·5 cm layer. These results demonstrate the importance of the
surface soil layer as a major source of microbial activity and inorganic N
production. There was a strong correlation between the distribution of
microbial biomass and the gross rate of mineralisation of soil organic N
within the soil profile.
Recharge estimation for the Liverpool Plains
Authors: Abbs K. , Littleboy M.
Published: August 2004

Dryland salinity is recognised as a major environmental concern on the
Liverpool Plains in north-eastern New South Wales. Previous hydrogeological
and dryland salinity studies have highlighted the importance of adopting
appropriate farming systems to reduce recharge into shallow aquifers. In this
study, we applied the cropping systems model PERFECT to investigate the
effects of climate, soil, and land use on recharge. Model inputs were derived
from a range of sources including historical weather data, soil survey data,
and information from landholder surveys. We investigated 47 different soils
identified in a published soil survey covering approximately 280 000 ha of the
Liverpool Plains.
This study demonstrated a significant variation in soil physical properties
and estimated recharge within soil types and illustrates the dangers of
generalising soils into broad groupings. For example, under a wheat-sorghum
rotation, predicted average annual recharge for soils classified as black
earths ranged from 28 to 80 mm. Similar variability of predicted drainage is
evident within other Great Soil Groups.
The results reveal that response cropping alone will not significantly reduce
recharge for all soils. Considering one black earth soil, average annual
recharge is predicted to be 48 mm for a wheat-sorghum rotation, 22 mm for a
response cropping rotation, and 8 mm for a lucerne{response cropping
rotation. Therefore, including lucerne within a response cropping system is of
benfit in reducing recharge. For all soil types, least recharge is predicted
for permanent pasture but this land use is not an attractive option to farmers
given the diversity of farming systems in the region. However, for some soils,
continuous pasture is appropriate because excessive recharge is estimated for
all cropping systems.
This study has extended previous modelling work in the region as it considered
a much wider range of soil types and cropping systems than previously
investigated. Such a modelling approach permits the quantification of the
effects of climate, soil type, and land use on recharge below the root-zone.