bluuebunny/crossref_metadata_2025 huggingface dataset:
Phosphorus leaching in sandy soils .I. Short-term effects of fertilizer applications and environmental conditions
Authors: Weaver DM , Ritchie GSP , Anderson GC , Deeley DM
Published: April 2005

The consequences of previous as well as current environmental conditions and management practices on the potential for phosphorus (P) to be lost by drainage from sandy soils in the short term (< 1 year) were studied in the laboratory and the field. The potential for P losses by drainage was estimated by measuring soil solution P levels and rapidly released P. Rapidly released P was measured by determining the concentration of dissolved inorganic P contained in filtered (<0.45 pm) soil solutions after incubating soil at saturation for 15 min at ambient temperature. In the laboratory, sandy soils were incubated with ordinary superphosphate, coastal superphosphate (a granulated mixture of equal parts of superphospate, rock phosphate and elemental sulfur) or lime-superphosphate (a lime-reverted superphosphate with 18% kiln dust) and sequentially desorbed with deionized water. The effects of the extent of leaching, fertilizer type, application rate and the time of contact with the soil on soil solution P levels were investigated. The influence of annual pasture death and summer rainfall on rapidly released P in soils that had been pre-treated by leaching were also investigated. Phosphorus concentrations decreased logarithmically in the successive supernatants of the sequentially desorbed soils. More P was desorbed from soils incubated with superphosphate and lime-superphosphate than soil incubated with coastal superphosphate. At each level of pre-leaching, the P concentrations in the soil solution increased with increasing time. The level, to which the P concentration in the soil solution increased at each time, decreased with increased extent of pre-leaching. The addition of P fertilizers increased the concentration of P in the soil solution. The concentrations increased with increasing application rate and were much higher for superphosphate than for coastal superphosphate; however, there was little effect of contact time on soil solution P levels. Rapidly released P levels after leaching increased during a period of no further leaching. Additional moisture or plant material during this period of no further leaching increased the rate and extent to which rapidly released P increased. Monitoring of rapidly released P in the 0-2, 2-5, 5-10 and 10-20 cm layers of field plots, with and without applications of superphosphate, showed that sampling depth, water flow path, fertilizer management, rainfall pattern and background P levels would affect the estimate of short-term P losses. Rapidly released P in the 0-2 cm layer varied markedly with time and was higher (P < 0.05) than that in lower soil layers. Rapidly released P increased after the winter and spring rains diminished and then decreased after the rains commenced again at the end of the summer. A possible annual cycle of P in sandy soils in a mediterranean climate is postulated by considering the laboratory and field data in combination.
Effects of rainfall variability on the efficacy of soil phosphate tests for wheat on semi-arid soils
Authors: Holford ICR , Corbin EJ , Mullen CL , Bradley J
Published: April 2005

Yield response data from 92 phosphate/nitrogen field experiments were used to evaluate and calibrate eight soil phosphate tests (Bray1, Bray2, alkaline fluoride, Mehlich, Truog, lactate, Olsen and Colwell) on semi-arid wheat-growing soils of central New South Wales. The effects of some aspects of year-to-year variability in rainfall characteristics on the efficacy and critical values of soil tests were also investigated. The order of efficacy of the soil tests was similar to that on the central western slopes (57 experiments) and northern region (48 experiments) of New South Wales. Lactate was not only the most effective test, but it was the only test that had the same critical value (18 mg kg-1) for the three regions. The actual efficacy of most soil tests in this semi-arid region was lower; apparently because the year-to-year variability in the annual average rainfall was greater than in the other two regions. Some or all of the soil tests were significantly related to yield responsiveness in three of the five individual years (1966-70) of the experimental period. In the other two years, relationships were vitiated by either semi-drought conditions (1967) or late frosts (1969). In 1970, when rainfall conditions were most favourable to yield response, average response curvature was lower and soil test critical values were higher than in the other years.
The vertical movement of zinc on sandy soils in southern Western Australia
Authors: Brennan RF , McGrath JF
Published: April 2005

Fertilizer zinc applied to the surface of an acid sand of low cation exchange capacity remained close to the soil surface even after 1438 mm of rain. At levels of zinc typically used in agriculture and forestry (0.7 kg ha-1 Zn) there was no movement of zinc below 2.5 cm. Where zinc was applied at 22.5 kg ha-l, 95% of the applied zinc could be accounted for in the top 5 cm. At the higher rate of zinc application (68 kg ha-1 Zn), 37% of the applied zinc was recovered below 5 cm.
A multivariate analysis of alluvial terrace soils of the clarendon and cranebrook formations, Nepean River, NSW
Authors: Atkinson G
Published: April 2005

The techniques of cluster analysis and principal component analysis (PCA) were applied to soils data from two Pleistocene alluvial terraces on the Nepean River, N.S.W., the Clarendon and Cranebrook Formations, to address issues raised in the literature regarding their stratigraphic relationships. A total of 160 profiles were sampled at four fixed depths to 1 8 m. Profiles were located in four 1000 by 400 m sample areas, two on each terrace. Soil samples were analysed for colour, pH, and 2.8 M HCl extractable Fe2+, Mn2+, Na2+, K+, Ca2+ and Mg2+. Data were analysed by using whole profiles as the soil entities. One branch of the dendrogram resulting from the cluster analysis contained soil profiles exclusively from sample areas on the Cranebrook Formation, whilst the other branch contained profiles exclusively from sample areas on the Clarendon Formation. Soils typical of the Lowlands Formation, Londonderry Clay and minor subdivisions within the terraces could be distinguished on the dendrogram. Similar subdivisions could also be observed on a PCA scattergram. The Clarendon and Cranebrook Formations are complex units which contain minor terrace features. Each has a distinctly different suite of soils which is consistent with their continued designation as separate stratigraphic units. The Lowlands Formation can be separated from the Cranebrook Formation upstream of Castlereagh and the Clarendon Formation should have its southern boundary to the Londonderry Clay moved north towards Richmond and its stratigraphy redefined.
The role of mulch and its architecture in modifying soil temperature
Authors: Bristow KL
Published: April 2005

Both the quantity and architecture of a surface mulch affect its performance in modifying the soil microenvironment. In this paper, temperature under two simple mulch architectures is compared and contrasted with that of bare soil in a tropical environment. In mulch treatments the quantities of mulch per unit area were similar, but elements in one treatment were horizontal (forming a 5 cm layer) while in the other they were vertical (forming a 22 cm layer). Temperatures were recorded for several days as the soil dried following a storm which saturated the mulch and surface soil. The bare soil dried more rapidly than that with mulch, so that by the fourth day its hourly maximum surface temperature was 8�C higher, and that at 2 5 cm depth was 3�C higher, than soil temperatures under the mulch. Significant differences in soil temperatures under the two mulch treatments only appeared several days later, as subtle differences in the partitioning of energy by the two mulch canopies became more apparent with drier conditions. By the twelfth day, the maximum surface temperature under the vertical mulch was 7�C higher than that under the horizontal mulch. Minimum soil temperatures were never more than 2.5�C different between the bare and mulched treatments and converged with drying. In both mulch treatments, the mulch elements near the soil surface experienced greater temperature extremes than those at the top of the mulch layer. The range in element temperature was slightly greater in the horizontal mulch treatment than in the vertical mulch treatment, where the element temperatures were more closely tied to air temperatures. The first few days following rain are crucial for seedling establishment in the semi-arid tropics and it appears from this study that mulch architecture is of minor importance during this period.
Modified square root of time relation to predict evaporation trends from bare soil
Authors: Jalota SK , Prihar SS , Gill KS
Published: April 2005

The existing methods of calculating cumulative evaporation (CE) from water transport theory pose a problem of availability of the governing parameters of the soil and atmospheric evaporativity. An empirical relation between CE, inclusive of the constant rate stage, and its time limit is not available. We investigated relations between CE and time (t) for different evaporativities (4). Estimates of CE by using the empirical relations between CE, t and vt agreed well with the observed values: where tf is the duration of the constant rate stage which can be computed from K and E0 K is the r,egression coefficient of CE on vt and b is the intercept. The results indicated that the duration of the constant rate stage decreased with increasing E0 and increasing redistribution time (T); CE under a lower E0 can exceed that under higher E0. Evaporation rate during the falling rate stage is dependent upon E0. For the same E0, the duration of the constant rate stage was higher in silt loam than in sandy loam.
Phosphorus cycling in wheat pasture rotations .I. The source of phosphorus taken up by wheat
Authors: Mclaughlin MJ , Alston AM , Martin JK
Published: April 2005

Wheat plants (Triticum aestivum cv. Warigal) were grown in the field in a solonized brown soil (Calcixerollic xerochrept) to which 33P-labelled medic residues (Medicago truncatula cv. Paraggio) and 32P-labelled fertilizer had been added. Amounts of 31P, 32P and 33P in the wheat plants were determined at 7, 18, 32, 46, 61, 81 and 95 days after sowing. The 32P uptake by the wheat plants increased throughout the experiment and reached 11 -6% of the isotope applied by 95 days. Of the 33P applied in the medic residues, 5 -4% was recovered in the wheat plants. Most of the P taken up by the wheat plants was from soil P (i.e, from sources not added that season).
Phosphorus cycling in wheat-pasture rotations. III. Organic phosphorus turnover and phosphorus cycling
Authors: Mclaughlin MJ , Alston AM , Martin JK
Published: April 2005

The incorporation of 32P and 33P from 33P-labelled fertilizer and 33P-labelled pasture residues into organic and inorganic fractions of soil P was studied in a solonized brown soil (Calcixerollic xerochrept) cropped to wheat (Triticum aestivum). Most of the plant residue 33P was present as inorganic P at the time it was added to the soil, but only 7 days later almost 40% had been incorporated into organic P fractions of the soil. As the fertilizer was banded near the soil surface at sowing, little of the 32P from the 32P-labelled fertilizer was incorporated into organic forms, even after 95 days. From a knowledge of the P uptake by the plants and microorganisms, an integrated P cycle for this soil under wheat-pasture rotations was developed. We propose that fertilization of the pasture phase of the rotation stimulates the build-up of residual inorganic and organic P, while fertilization of the wheat phase predominantly stimulates the accumulation of inorganic forms of P in the soil.
A dual radiotracer study of transformations of organic, inorganic and plant residue phosphorus in soil in the presence and absence of plants
Authors: Friesen DK , Blair GJ
Published: April 2005

The rates of transfer of P from plant residues added to an acid soil into various soil P pools and the rates of transfer of inorganic P from soil solution into other soil P pools were studied by simultaneous use of 32P-labelled plant matter and 33P-labelled soil in the presence and absence of growing plants. Equilibration of 33P-labelled phosphate solution added to soil reached a steady state with soil ALP and Fe-P pools within 1 day after addition. The Fe-P pool was much more stable than the A1-P pool since it was not depleted by cropping. This non-labile pool 'fixed' over 30% of the 33P added and similar amounts of the 32P released from plant residues. About 50% of the 32P from plant residues was found in inorganic P pools 11 days after addition. This rapid release was attributed to the presence of soluble inorganic P in the residues. A further 10% was released slowly over the remainder of the experiment. Cropping only marginally slowed rates of transfer of inorganic and released residue P into non-labile pools. Cropping had no effect on the rates of release of P from crop residues.
The effects of soil water content and bulk density on the compactibility and soil penetration resistance of some Western Australian sandy soils
Authors: Henderson C , Levett A , Lisle D
Published: April 2005

Quantitative models to predict the effects of soil compaction on wheat yields are being developed for the northern sandplains of Western Australia. An understanding of the relationships between soil water content (W), bulk density (p), compactibility and soil penetration resistance (P) is required. Thirteen subsoils from W.A. sandplain soils were tested for compactibility. As the amounts of very coarse sand or clay in the soil increased, the maximum density (�max.) achieved with a standard compactive effort also increased, while the critical soil water content (Wcrit,.) for maximum compactibility declined. The effects of p and W on P were investigated for five of the soils. The value of P was only slightly affected as W was reduced to less than 70% of the field capacity water content. As the soils were dried further, P increased exponentially. At all water contents, an increase in p was found to markedly increase P. Particle size distribution could be used to predict �max. and Wcrit., but could not be related to the effects of changes in p and W on P. The implications for the measurement and effects of soil compaction in the field are discussed.
Erosion of a gully in duplex soils - Results of a long term photogrammetric monitoring program
Authors: Sneddon J , Williams BG , Savage JV , Newman CT
Published: April 2005

The development of a gully within an ephemeral stream channel was monitored over a 10 year period by using a direct contact measurement technique initially and then a photogrammetric technique. The latter was shown to have an accuracy of better than 0.05 m3 for each time of measurement. The volume of soil loss and gully headwall progression were very nearly linear with time, having values of 0.40 m3 yr-1 and 0.25 m yr-1 respectively.
Comparison of models for predicting available water capacity of burdekin soils Queensland
Authors: Ahern CR
Published: April 2005

Various models for predicting profile available water capacity (PAWC) from laboratory measurements were compared with published field values for the same sites. The intention was to choose the best model/s to predict PAWC, by using a database, for a wide range of soils in the Burdekin Irrigation Area, North Queensland. Effective rooting depth for all models was estimated from the chloride profile. It was found that the predictive abilities of all models used were dependent on soil types. A conventional model (ASWC) based on the difference between water retained at -33 and -1500 kPa matric potentials was higher (P < 0.01) than field measured PAWC. An empirical model (PAWC2) based on cation exchange capacity (CEC) and depth was suitable only for cracking clays and sodic duplex soils. Another empirical model (PAWC1) based on -1500 kPa water retained and depth, predicted field PAWC particularly well on cracking clays, sodic duplex and related soils. There were strong indications that the PAWC1 model is also suitable for the better drained, lighter textured soils but there was a shortage of comparable field data to confirm this. The practical implication of these findings was that an analytical database can be used to predict PAWC on many Burdekin soils, providing immediate assistance to those designing irrigation channels and farm layouts.
A simple technique for collecting large soil profiles for display
Authors: Mitchell PB , Paton TR
Published: April 2005

A flexible peel technique is described which has been used on many soil types to produce display profiles as large as 2x3 m. The technique uses inexpensive latex emulsion and muslin, requires no special expertise or equipment and the peels have an effective lifetime of more than 10 years.
Efficacy of various soil phosphate tests for predicting phosphate responsiveness and requirements of clover pastures on acidic tableland soils
Authors: Holford ICR , Crocker GJ
Published: April 2005

The efficacies of six different soil phosphate tests (Bray1, Bray2, alkaline fluoride, lactate, Olsen and Colwell) for predicting yield responsiveness and phosphate requirements of white clover pastures were investigated in 41 experiments over five years on acidic soils of the Northern Tablelands of New South Wales. The results contrasted with those obtained on slightly acid-to-alkaline wheat-growing soils and supported the dual hypothesis that a different type of phosphate extractant is required on acidic pasture soils from that required on more alkaline wheat-growing soils, and that phosphate sorptivity is of little importance on more acid soils. The Bray1 test was the most effective, and the lactate test least effective, in predicting responsiveness and fertilizer requirement. All soil tests, except Bray2 and lactate, were more effective on these acidic soils than on more alkaline wheat-growing soils. This was partly caused by a significant positive correlation between values of the more effective tests and yield response curvatures. However, there was no correlation between phosphate sorption and response curvature. The critical values for Bray1, fluoride and bicarbonate tests were similar to those on wheat-growing soils, but those for Bray2 and lactate were somewhat higher. Critical values for the Colwell test tended to increase with increasing phosphate sorptivity.
Revegetation in an iron ore mine - Nutrient requirements for plant growth and the potential role of vesicular arbuscular (VA) mycorrhizal fungi
Authors: Jasper DA , Robson AD , Abbott LK
Published: April 2005

Revegetation after iron-ore mining in the Pilbara region of Australia is difficult because of the harsh climate and because the material to be revegetated is likely to have poor fertility and low microbial activity. In this work we defined the infectivity of VA mycorrhizal fungi in local soils and mine materials, and then the nutrient requirements for adequate plant growth in low-grade ore. Finally, we tested the hypothesis that addition of phosphorus to low-grade ore, and inoculation with VA mycorrhizal fungi, increases the growth of Acacia pyrijolia. The VA mycorrhizas were formed only in soil collected from sites dominated by Triodia pungens. A. pyrifolia nodulated only in soil from sites dominated by A. aneura. In low-grade ore, phosphorus deficiency was the major limitation to plant growth. Inoculation with a Glomus sp. resulted in up to 70% increases in dry matter production at low rates of phosphorus. The response to phosphorus or inoculation with VA mycorrhizal fungi was limited by nitrogen deficiency.
Changes in surface soil properties of vertisols under dryland cropping in a semiarid environment
Authors: Chan KY , Bellotti WD , Roberts WP
Published: April 2005

Changes in the properties of Vertisols in the Walgett area, north-western New South Wales, under the present continuous cropping system were investigated. Soils (0-0.1 m) from four locations which had been cultivated for 8-50 years were collected and a range of physical, chemical and biological properties were measured. Adjacent native pasture soils which had never been cultivated were used for comparison. Associated with a substantial reduction in organic matter levels (up to 40%), the cultivated Vertisols were found to have higher pH, lower extractable (Bray No. 1) phosphorus, lower structural stability and lower biological activity. The increase in pH of soils under cultivation (1 : 5 soil: water) varied from 0.5 units (8.3-8.8) in a grey clay under 20 years of cultivation to 1.5 units (7.0-8.5) in a brown clay which had been cultivated for 50 years. The higher pH may be the cause of lower extractable phosphorus found in the cultivated soils. Lower biological activity was detected in all the cultivated soils when compared with adjacent pasture soils. Added carbon and nitrogen substantially increased the biological activity of all the cultivated and pasture soils; however, in three of the four soils, carbon dioxide production of the amended cultivated soil remained lower than the corresponding amended pasture soil. For Vertisols, a pasture phase may be important in preventing alkalinization as well as in maintaining P availability, in addition to the commonly recognized benefits such as maintaining soil structure and nitrogen levels.
Dynamics of microbial-C, N-flush and ATP, and enzyme activities of gradually dried soils from a climosequence
Authors: West AW , Sparling GP , Speir TW , Wood JM
Published: April 2005

Three silt loam soils from a climosequence (1000-2700 mm annual rainfall) were gradually dried from field moisture content to air-dryness at 25�C in the laboratory. Microbial C measured by substrate-induced respiration (SIR), fumigation-incubation (FI) or fumigation-extraction (FE), microbial N-flush measured by FI and FE, microbial ATP content and soil phosphatase and sulfatase activities were monitored throughout the drying period (approx. 60 h). All indices declined as the gravimetric soil water content (W) decreased until reaching air-dryness. Significant declines in the biomass sometimes occurred only following a large decrease in W, dependent on the soil. In general, when microbial C and N-flush declined, the rates of decline were linearly correlated with W. However, ATP and soil phosphatase were exponentially related to W. When expressed as a ratio of the total change in microbial indices against the total change in W for the whole drying period, the ratios were consistent between the soils. Agreement between the SIR and FE estimates of microbial C, whilst significant (r = 0 58***), was poor, especially for the low rainfall soil, although the FE C- and N-flushes correlated well (r = 0-76***). In contrast, the FI C- and N-flushes correlated very poorly (r = 0.30**) and were not significantly correlated with W or the other indices. ATP and soil phosphatase activity were strongly correlated (r = 0.89***). The reliability of the methods and the influence of soil moisture regimes on microbial survival are discussed.
Quantification of the effects of zero and mechanical tillage on a vertisol by using shrinkage curve indexes
Authors: Mcgarry D
Published: April 2005

The effect of zero versus mechanical tillage on the structure of the top 0.1 m of a Vertisol at Hermitage, near Warwick, Queensland, was examined by using indices derived from fitting three straight lines to soil shrinkage data. The data were generated from the slow drying of initially, near-saturated, SARAN-coated soil clods. Values of specific volume and the specific volume of air-filled pores were significantly greater in the mechanically tilled rather than the zero-tilled soil, showing that mechanical tillage has led to decreased bulk density and increased porosity in the surface layer of this soil.
Hydraulic conductivity of aqueous bentonite suspensions
Authors: Kirby JM , Smiles DE
Published: April 2005

In many circumstances, filtration of two-phase, solid-liquid systems can be described by theory based on Darcy's Law and an appropriate continuity equation. The theory requires that relations between the water content and (a) the water potential, and (b) the permeability are well defined. This paper describes experiments which permit calculation of both these relations in a water-bentonite suspension. The permeability function calculated directly from steady state experiments compares with that calculated indirectly from transient experiments, thus confirming the basic assumptions of the theory. It is shown that both the water content-water potential, and the water content-permeability relations are sensitive to solution salt concentration. However, the water potential-permeability relation is nearly independent of salt concentration, thus allowing considerable simplification in the information sufficient and necessary to characterize this system.
The influence of flow discharge on sediment concentrations in raindrop induced flow transport
Authors: Kinnell PIA
Published: April 2005

In laboratory experiments, gentle flows over 200 �m sand were impacted by 2.7 mm drops travelling at near terminal velocity. The sediment concentrations generated by raindrop induced flow transport (RIFT) decreased with discharge. The decrease was associated with changes in flow depth. Variations in discharge associated with changes in flow velocity did not significantly influence the sediment concentration. The non-significant influence of flow velocity on sediment concentration was the result of a direct relationship between flow velocity and the frequency of drop impact in the active region associated with the movement of soil past any given point on the surface.
Boron toxicity in soil solution
Authors: Aitken RL , Mccallum LE
Published: April 2005

The relationship between soil solution boron concentration and the dry-matter accumulation and boron concentration in sunflower (Helianthus annuus cv. Hysun 31) was investigated in a 14-day study in a controlled environment. Plants were grown in each of six soils previously equilibrated with various levels of boron applied as H3BO3. The soil, wet to 10 kPa matric suction, was retained in polypropylene containers and the soil solution was extracted by centrifugation from the entire undisturbed soil volume immediately after the top growth had been harvested. Above a threshold of 1.9 �g B mL-1 in soil solution, yield reductions due to boron toxicity occurred. In the toxicity range there was a linear relationship between relative dry matter yield and log10[B] in soil solution. At high levels of boron, the relationship between boron concentration in plant tops and hot 0.01 M CaCl2-extractable boron depended on soil type, whereas the relationship between plant boron concentration and soil solution boron concentration did not depend on soil type. It is suggested that, at high levels of boron, plants were responding to soil solution boron (intensity), while hot 0.01 M CaCl2-extractable boron estimates a quantity factor. The results obtained indicate that the apparatus and technique used in this study could be used to derive toxicity threshold concentrations for a range of plant species.
Soil phosphorus parameters affecting phosphorus availability to, and fertilizer requirements of, maize (Zea mays)
Authors: Moody PW , Aitken RL , Compton BL , Hunt S
Published: April 2005

The phosphorus status of each of 26 surface soils from Queensland was characterized by laboratory measurements and a glasshouse experiment. The glasshouse trial investigated the response between applied P in each soil and maize (Zea mays) dry matter yield. In the laboratory, the quantity of soil P was estimated by extraction with 0.5 M NaHCO3 (PB), and the intensity was estimated by soil solution P, 0.005 M CaCl2 extraction and equilibrium phosphorus concentration (EPC). Phosphorus-sorption curves were established for each soil and the data were used to derive the buffering index (BI) and equilibrium buffer capacity (EBC). Four single-point sorption indices were also determined. The desorption buffer capacity (dBC) of each soil was obtained in the laboratory by equilibrating soil samples with anion exchange resin for periods ranging from 0.1 to 18 h. This paper reports the relationships between the various P parameters and (i) the P uptake by maize (Zea mays) grown in untreated soil, and (ii) the amount of added P required for 90% maximum yield. Intensity, as estimated by EPC, was significantly (P < 0.001) correlated with P uptake. Any of the BI, EBC or the single-point sorption indices significantly improved the variation in P uptake accounted for by PB alone, but not to the same level as that obtained with EPC alone. When PB was combined with dBC, more variance was accounted for in P uptake than by using any of the adsorption buffer capacity measurements. The effects of quantity, intensity and buffer capacity on P availability are discussed in terms of their effects on P diffusion. For the suite of soils studied, it is concluded that intensity is the prime factor governing availability, and that the usefulness of adsorption buffer capacity measurements depends on their correlation with desorption buffer capacity. Variation in P requirement was best described by a combination of EPC and the Mitscherlich curvature coefficient, or EPC and one of the single-point sorption indices. As the single-point sorption indices were highly correlated with desorption buffer capacity, adsorption buffer capacity, and the curvature coefficient, they offer a convenient measure of the sorption properties of a soil.
Effects on seal properties of changes in drops energy and water salinity during a continuous rainstorm
Authors: Agassi M , Shainberg I , Morin J
Published: April 2005

The effect of changes in rainfall energy and water salinity, during a continuous simulated rainstorm, on seal properties was tested in a silty loam soil (Calcic Haploxeralfl with medium (9.0) and low (2.5) exchangeable sodium percent (ESP) values. Saline water (EC = 5 -6 dS m-1) and distilled water were rained at two energy levels: high energy with kinetic energy of 22.9 J mm-1 m2, and low energy with kinetic energy of <0.01 J mm-1 m-2. A seal may be fully or partially developed. The seal formed by a distilled water rain of high energy and sufficient duration is fully developed. A seal formed by rain with low energy, or by high-energy rain of short duration, or by saline rainwater of high energy and long duration, is a partially developed seal. A fully developed seal is stable and its permeability responds only to simultaneous changes in electrolyte concentration and rain energy. Conversely, a partially developed seal is not stable and its permeability responds to changes in electrolyte concentration only.
Aluminum determination in soil solution. 2. Short-term colorimetric procedures for the measurement of inorganic monomeric aluminum in the presence of organic acid ligands
Authors: Kerven GL , Edwards DG , Asher CJ , Hallman PS , Kokot S
Published: April 2005

Colorimetric procedures were developed for the determination of inorganic monomeric aluminium (Al) in the presence of organic ligands including high molecular weight fulvic acids and short chain carboxylic acids. The procedures take advantage of marked differences in reaction rate between the chromogens aluminon and pyrocatechol violet (PCV) and aluminium in either free inorganic forms or organically complexed forms. The aluminon method uses a 30 s reaction and has a working range for total Al concentrations between 20 and 250 PM. The more sensitive PCV method uses a reaction time of 60 s and provides a linear calibration line in the range 0.2-25 �M. Both methods are calibrated by using standard solutions containing known total A1 concentration prepared with varying ratios of inorganic monomeric and organically complexed Al. The determination of Al in soil solution and its fractionation into inorganic monomeric and organically complexed forms requires the measurement of total Al in filtered soil solutions by inductively coupled plasma atomic emission spectroscopy (ICPAES) and the use of one of the short reaction time colorimetric procedures. Limited testing on soil solutions from acid, Al toxic soils showed better agreement between inorganic monomeric Al concentration determined by the new procedures and relative yield data than that obtained by existing colorimetric methods.
Efficacy of different phosphate application methods in relation to phosphate sorptivity of soils
Authors: Holford ICR
Published: April 2005

The efficacy of top-dressing, shallow and deep subsurface placement, and uniform mixing of phosphate through the top 17 cm of soil was compared on six soils varying in sorptivity from 100 to 10000 ml g-1 in a glasshouse experiment. Shallow banding at 5 cm depth was the most consistently superior method of application, whether effectiveness was measured as yield response in the first crop (wheat), residual effects in the second crop (clover), or cumulative recovery of applied phosphate during 27 months of wheat and clover. Top-dressing was equally effective in the most weakly sorptive soil but inferior in the most strongly sorptive soil. Deep placement at 15 cm and top-dressing were generally the least effective methods. The almost equivalent effectiveness of phosphate-soil mixing to shallow banding, regardless of sorptivity, suggests that the important factor in maximizing fertilizer effectiveness is its positional availability in the root zone rather than restriction of chemical immobilization by fertilizer concentration in bands. The apparent recovery of applied phosphate from most soils declined most sharply in the second year after application and thereafter remained constant or even increased up to 27 months after application. Total recovery of applied phosphate was similar over the normal range of sorptivities (100-2500 ml g-l) but it was lower on the very highly sorptive soil.
Influence of soil moisture regime on the respiration response of soils subjected to osmotic stress
Authors: Sparling GP , West AW , Reynolds J
Published: April 2005

The influence of the soil moisture regime on the tolerance of the soil micro-organisms to increased osmotic stress was examined by laboratory tests with a range of New Zealand soils. Soils from various climatic regions (moist, intermediate and dry) were amended with glucose-NaCl solutions, incubated for 0.5 h, and the respiration rate over the following 2 h was used as a measure of the response of the microbial biomass to the changed osmotic potential. Osmotic potentials were varied between -4 and -80 bar by altering the concentration of NaCl. Air-drying the soils at 25�C decreased the respiration response of the microbial biomass by 3-60% but had little effect on the tolerance of the surviving populations to decreased osmotic potentials. In general, the soils showed the same patterns: an osmotic potential of -23 bar decreased the respiration response by 28-45% (18-44% after air-drying) and a -80 bar potential decreased it by 64-86% (52-84% after air-drying). For the majority of soils, a consistent relationship was obtained between the respiration rate of the moist soils and the osmotic potential applied. A reasonable prediction of the respiration response after air-drying could be obtained from the respiration response of moist soils at -25 bar osmotic potential.
The significance of (surface) physical and chemical properties in determining soil surface condition of red earths in rangelands
Authors: Greene RSB , Tongway DJ
Published: April 2005

The surface layers of a red earth near Cobar, N.S.W., have been classified into four condition classes by using attributes that are readily observable in the field. These classes provide a reliable estimate of potential dry matter production. Soil samples from the three depths 0-1, 1-5 and 5-10 cm of each class were analysed for various physical and chemical properties. Soil surface resistance was measured in the field. Field measurements of infiltration were carried out at supply potentials of +10 and -40 mm by using the disc permeameter. Differences in physical and chemical properties of the classes occurred mainly in the 0-1 cm layer. Below 1 cm there was very little difference in properties between the four classes. The 0-1 cm depth of the class 1 soils (most productive) contained significantly (P=0.05) higher amounts of organic matter, available nitrogen and exchangeable magnesium than the class 4 soils (least productive). Class 1 soils had higher aggregate stabilities in the 0-1 cm layer and lower soil surface resistance than class 4 soils, indicating more favourable soil physical conditions for seed germination and emergence. Aggregates of all classes underwent considerable dispersion in water when subjected to mechanical stress. At a supply potential of +10 mm, class 1 soils had a significantly (P=0.05) higher infiltration rate than class 4 soils. However, at a supply potential of -40 mm, there was no difference in infiltration rate between classes. Scanning electron microscope (SEM) micrographs showed that cryptogamic material on the surface of class 1 soils resulted in a porous, well aggregated structure compared with the dense, compacted structure of class 4 soils. The differences in physical and chemical properties support earlier micro-morphological evidence that the classes 1-4 essentially represent an erosional sequence from no erosion (class 1) to strongly eroded (class 4). The importance of these physical and chemical properties of different soil classes in determining productivity of rangeland soils is briefly discussed.
Relationships between soil morphology and soil properties relevant to irrigated and dryland agriculture
Authors: Mckenzie NJ , Macleod DA
Published: April 2005

A number of morphological attributes are commonly assumed to serve as surrogates for properties that cannot be practically measured on a routine basis This study investigates whether conventional soil morphology can be used for predicting soil properties of relevance to irrigated and dryland agriculture in the lower Macquarie Valley, N S W Measurements from 224 profiles were used to develop regression equations with morphological properties as explanatory variables Response variables included gravimetric moisture contents at -10 and -1500 kPa, available water capacity, ail-filled porosity, ESP, dispersion index, the coefficient of linear extensibility, bulk density and CEC The relationships between field texture and particle size classes were also determined Conventional sod morphology provided only moderate predictions of the agronomically more important properties In the lower Macquarie Valley, texture and colour were the most useful explanatory variables Most of the remaining morphological properties, and in particular conventional descriptors of structure, contributed little to improving prediction Options for more cost-effective and direct measurements, especially of profile macrostructure are considered.
Deep cementation in late quaternary sands near Westport, New Zealand
Authors: Ross CW , Mew G , Childs CW
Published: April 2005

Deeply cemented quartzofeldspathic and ilmenitic sands occur on and beneath uplifted late Quaternary marine terrace surfaces over wide areas south of Westport on the west coast of the South Island. These terraces are weakly dissected, but are mainly flat to rolling. Rainfall averages about 3000 mm per year. Present vegetation consists of pasture, scrub and rush/fern associations which have replaced podocarp forest. Cementation of sands has resulted in impeded drainage, limited rooting volumes for trees and crops, and other limitations to land development. Two soil series, Charleston and Marris, were studied, as they were distinguished by having different forms of cementation in the field. Techniques used to investigate cementation included the determination of Fe, Al and Si contents by extraction with standard chemical reagents, X-ray diffractometry to identify minerals of short-range order, SEM to examine microstructures, EDAX to determine elemental composition, and heating in an induction furnace to evaluate C content. Two apparent causes of cementation were identified, namely ferrihydrite in the Charleston soil, and allophane with humus-aluminium complexes in the Marris soil. Microstructures of sand cemented by these materials were clearly different. In the Charleston soil, iron-rich material coating sand grains and bridging between them is smooth and gel-like and has a fine globular appearance under high magnification. In the Marris soil, the cementing material has a rough-textured fibrous appearance. The contrasts in types of cementing agents are thought to be related to firstly, differences in physiography at time of formation and secondly, different drainage conditions related to topographic position.
Utility of the factual key and soil taxonomy in the Lower Macquarie Valley, NSW
Authors: Mckenzie NJ , Austin MP
Published: April 2005

The utility of the Factual Key and Soil Taxonomy was tested by using comprehensive soil survey data from the lower Macquarie Valley, N.S.W. The aim was to assess whether the two classification schemes partitioned soil variation efficiently and to establish their usefulness for predicting variables not used during profile allocation. A numerical taxonomic method was used to generate a local classification which served as a benchmark to assess the two national systems. The effectiveness of the three classifications was determined by comparing the proportion of variation accounted for in a range of soil properties of direct relevance to irrigated and dryland agriculture. The Factual Key and Soil Taxonomy were found to be equally poor for predicting relevant soil properties. Both systems arbitrarily subdivided important local modalities. The variation accounted for by the numerical classification was 20-30% greater. The result demonstrates the practical advantages of a local classification and the reality of Butler's taxonomic hiatus.
Evaluation of soil structure by using computer-assisted tomography
Authors: Phogat VK , Aylmore LAG
Published: April 2005

Computer assisted tomography applied to gamma ray attenuation (CAT scanning) has been evaluated as a method for directly measuring the spatial distribution of soil macroporosity and for monitoring changes which occur during wetting and drying processes, in a non-destructive manner. Total porosity calculated from the bulk density of soil and glass tube samples varying in bulk density from 0.759 to 1.602 g cm-3 correlated well with total porosity calculated from CAT scan data. The system was able to detect changes in bulk density for a loam soil of the order of 16 mg cm-3, and objects of 2.0 by 2.0 mm dimensions could be pictorially resolved in the scanning plane. Statistically, the system resolves pixels differing by at least 6.14% in attenuation coefficient value from surrounding pixels. Average macroporosity and the spatial and frequency distribution of macroporosity for soil samples were determined by assigning the value of zero macroporosity to pixels having gamma attenuation coefficients corresponding to the bulk density of a soil aggregate, 100% macroporosity to pixels with zero attenuation coefficients and proportional values to pixels with intermediate coefficients. The CAT scanning of soil samples before and after a wetting and drying cycle illustrated the greater reduction in macroporosity for soil wetted under flooding compared with that wetted under capillary action. The CAT scanning clearly has considerable potential for studying the spatial distribution of soil macrostructure and for monitoring the changes in macroporosity which occur during wetting and drying processes in soil columns.
Chemical attributes of some Queensland acid aoils. I. Solid and solution phase compositions
Authors: Bruce RC , Warrell LA , Bell LC , Edwards DG
Published: April 2005

Samples from surface and subsoil horizons of 91 acid soils in Queensland were analysed for pH, EC, Cl, exchangeable cations and organic C. Generally low values for EC, Cl, exchangeable Na and exchangeable K were found in surface soils and subsoils. Higher values of organic C, exchangeable Ca and pH occurred more frequently in surface soils, while exchangeable A1 and exchangeable Mg were generally higher in subsoils. A correlation matrix gave significant, but not strong, linear correlations between soil attributes associated with soil acidity (pH and Ca, Mg and Al saturations). Soil solutions were extracted from surface and subsoil horizons of 48 of these acid soils and analysed for pH, EC, Na, K, Ca, Mg, SO4 and monomeric Al. Ionic strengths and activities of monomeric Al species were calculated. Soil solution pH tended to be lower in subsoils than in surface soils, but very few values were <4.5. Ionic strengths were mostly <8 mM, with mean values of 5.3 mM for surface soils and 2.4 mM for subsoils. Subsoils had lower mean concentrations of Ca, Mg and K, and similar concentrations of Na, compared with surface soils. In both groups, molar concentrations followed the order Na > K ~ Mg > Ca. Mean values for activities of AlOH2+, Al(OH)2+, Al(OH)3 and AlSO4+ in surface soils exceeded those for subsoils, but activities of Al3+ were similar. Higher activities of Al species in surface soils resulted from higher monomeric Al concentrations, but it was concluded that the analytical method overestimated monomeric Al in surface soils, probably by including some of the soluble organic Al complexes present. The best correlation between pH and Al species was with Al3+ , particularly in subsoils (r2 = 0.913). Activity of Al3+ in subsoils was correlated with ionic strength (r2 = 0.666) when both were expressed on a logarithmic scale.
Effect of electrolyte concentration on glucose decomposition in soil
Authors: Baldock JA , Oades JM
Published: April 2005

The influence of the electrolyte concentration of the soil solution on the ability of the soil biomass to decompose glucose was assessed by determining the residual glucose content of soil samples in a laboratory incubation experiment. For three amounts of glucose addition (0, 3.5 and 70 mg glucose g-1 soil), the electrolyte concentration of the soil solution was varied between that of deionized water and a 0.10 M CaCl2 solution. A significant decrease in the rate of glucose decomposition was only noted once the concentration of Ca2+ in the soil solution reached 0.10 M; however, after 125 h incubation, the extent Of glucose decomposition was not significantly influenced by changes in Ca2+ concentration. Therefore, increases in the electrolyte concentration of soils amended with gypsum or agricultural lime are not likely to inhibit the activity of the microbial biomass and its ability to decompose organic residues.
Deep infiltration - Significant or not
Authors: Brouwer J
Published: April 2005

For those involved with evaluating the effects on the water balance of changes in land use, it is always interesting and pleasing to see a report on a study involving paired catchments. One such report was presented by Prebble and Stirk (1988). From their study, Prebble and Stirk concluded that the killing of trees and establishment of improved pasture in an open grassy woodland did not affect evapotranspiration. While this result was not quite what they expected, they thought it could be explained by the fact that the killing of the trees resulted in an increase in wind run and in radiation to the grass. This in turn would have increased evapotranspiration from the grass, which would have compensated for the reduction in interception and evapotranspiration by the trees. This explanation, to some extent, ignores the observed increase in average soil water storage following the death of the trees. Perhaps, then, the answer to this water balance problem lies not in the evapotranspiration term, but in the increased soil water storage and associated increased deep drainage.