bluuebunny/crossref_metadata_2025 huggingface dataset:
Geostatistical analysis of cyst nematodes in soil
Authors: WEBSTER R. , BOAG B.
Published: July 2006

The numbers of cyst nematodes that live in agricultural soil vary both in time and space with important consequences when devising procedures for inspection and strategies for their control. We have examined the distributions of two species, Globodera rostochiensis and Hererodera avenue, in fields in the east of Scotland by counting their live cysts in the topsoil. Nested sampling and analysis showed that most of the spatial variation occurs within distances of 5 m to 50 m. Experimental variograms computed from transects and grid surveys appeared to be isotropic and bounded with a range of approximately 60 m. Both species are strongly aggregated. H. avenue occurred in large patches. Indicators for cyst counts of 1, 4 and 10 were created from the data. The experimental auto and cross variograms of these indicators were computed and models fitted to them. All of these variograms had the same spherical form as that of the original counts but shorter ranges, and the cross variograms had more structure, suggesting a border effect. Biologically, the distribution can be explained by the nematodes being spread by cultivation from initial fortuitous foci of infestation or control by nematophagous fungi or both.
Properties of soil kaolinites from south‐western Australia
Authors: SINGH B. , GILKES R. J.
Published: July 2006

The clay fraction of soils from south‐western Australia is dominated by kaolinite. These soil kaolinites give broad basal reflections (median value for WHH 001 =0.41° 2θ) and have poorly ordered structures. The median value of the Hughes & Brown crystallinity index for 35 soil kaolinites is 5.4 compared to 42.0 for mineral standard kaolinites. The median values for surface area and cation exchange capacity of soil kaolinites are 35 m2 g−1 and 56.7 mmolc kg−1, respectively, compared to 10 m2 g−1 and 4.8 mmolc kg‐ l for standard kaolinites. The dehydroxylation temperature of soil kaolinites is about 50 K lower than for standard kaolinites and decreases with increasing Fe content.

Soil kaolinite crystals are much smaller (c. 0.10 pm) and are irregular subrounded to rounded plates in comparison to the larger (c. 0.28 pm), perfectly hexagonal euhedral plates of Georgia kaolinite. Analytical electron microscopy of single soil kaolinite crystals indicates that the Fe content varies with an average value of c. 2.5% Fe,2O3. X‐ray diffraction line broadening data indicate that crystal size decreases as the Fe content increases. Crystal order also decreases with increasing Fe content. The P sorption maximum of soil kaolinite ranges from 486–654 μg P g−l and is thus about six times larger than for the clay fraction of Georgia kaolinite.
Computer simulation of metal ion—humic and fulvic acid interactions
Authors: MOUNTNEY A. W. , WILLIAMS D. R.
Published: July 2006

The humate model, RANDOM, was investigated in combination with the general speciation program, PHREEQE. After an initial investigation of cobalt(II)–humic acid and copper(II)–fulvic acid interactions this coupled code approach was modified to include a sensitivity analysis which identified the ligands which were statistically significant in any one system. Subsequent speciation modelling with these significant ligands is shown to produce a reasonable agreement between experimental and modelled data. The systems chosen to demonstrate the advantages of this approach were uranyl–humate and nickel(II)–humate interactions. Although this technique is not fully developed, it shows great potential for improving the predictive qualities of the RANDOM model.
The effect of pH on zinc adsorption by a lateritic soil in the presence of citrate and oxalate
Authors: CHAIRIDCHAI P. , RITCHIE G. S. P.
Published: July 2006

A change in the pH of the rhizosphere may alter the effect that organic ligands have on the concentration of Zn in the soil solution. To assess this effect, Zn adsorption by a lateritic soil was measured in the presence of 0, 1 and 3 mM of citrate and oxalate at nine values of pH ranging from pH 2 to 8. The concentrations of Zn and the ligands remaining in the solution were determined after 17 h shaking with the soil at soil:liquid ratio of 1:5. Subsequently, Zn speciation was calculated. The effectiveness of an organic ligand (L) in changing Zn adsorption was influenced by the sign of the charge of the Zn‐L complex, the point of zero salt effect (PZSE) of the soil, the pH of the soil solution and the quantity of the complex formed. When the pH was above the PZSE of the soil, citrate decreased Zn adsorption by up to 38% whereas it increased Zn adsorption by as much as 51 % when the pH was below the PZSE. Oxalate had a similar but smaller effect than citrate under the conditions of the experiment. Zn adsorption was correlated with the concentration of zinc citrate in both pH regions (r2>0.98) and with oxalate above pH 2.7. The increase in Zn adsorption at low pH could have been caused by the adsorption of negatively charged Zn‐L complexes.
The reaction between phosphate and dry soil. II. The effect of time, temperature and moisture status during incubation on the amount of plant available P
Authors: BRAMLEY R. G. V. , BARROW N. J.
Published: July 2006

Subterranean clover was grown in pots in which the only source of phosphate (P) was from bands of soil which had been incubated with P for a range of times, and at different temperatures, when either moist or air‐dry. The effectiveness of these incubated soils in supplying P to plants decreased with time of incubation. Effectiveness decreased after air‐dry incubation, though not as quickly as after moist incubation.

These results indicate that air‐dry storage of soil samples is to be avoided if the samples are to be assessed for their ability to supply P to growing plants. They also indicate that the cost‐saving to Australian farmers, derived from applying phosphate prior to the start of the growing season, may be balanced or even outweighed by a loss in fertilizer effectiveness due to the reaction between P and the soil in the weeks prior to germination of seed.
Temporal variation in the hydraulic conductivity of a tilled clay soil as measured by tension infiltrometers
Authors: MESSING I. , JARVIS N. J.
Published: July 2006

Steady‐state infiltration rates from tension infiltrometers were measured on ploughed and unploughed plots in a clay soil during the period June to October. Measurements were made both at the soil surface and at depths of 15 and 25 cm. Hydraulic conductivity in the water potential range zero to −11 cm was obtained using a piece‐wise exponential K(Ψ) function and Wooding's solution for infiltration from a circular source. A two‐line regression model showed excellent fits to paired (In KΨ) values on all measurement occasions. This may indicate the existence of a bimodal pore system, reflecting the contributions of macro‐ and mesopores to the measured K(Ψ) function. The break‐point potential dividing the two pore systems varied between c.−4 and −6cm. Significant variations in the K(Ψ) function between sampling occasions were found at the soil surface, but not at depths of 15 and 25 cm. Measured K(Ψ) values decreased during the growing season, particularly at potentials between −4 and −6 cm where reductions were up to one order of magnitude. This was attributed to soil structural breakdown by rain impact and surface capping or sealing. Hydraulic conductivity near the soil surface was significantly increased by disc harrowing in autumn. In contrast, no pronounced difference in the K(Ψ) function between ploughed and unploughed treatments could be discerned at 15 and 25 cm depths in the soil.
Losses of nitrate‐nitrogen in water draining from under autumn‐sown crops established by direct drilling or mouldboard ploughing
Authors: GOSS M. J. , HOWSE K. R. , LANE P. W. , CHRISTIAN D. G. , HARRIS G. L.
Published: July 2006

The leaching of nitrate‐N under autumn‐sown arable crops was measured using hydro‐logically isolated plots, about 0.24 ha in area, from 1984–1988. Fluxes of water and nitrate moving over the soil surface (surface runoff), at the interface between topsoil and subsoil (interflow), and in the subsoil (drainflow) were monitored in plots with mole‐and‐pipe drain systems (drained plots); surface runoff and interflow only were monitored in ‘undrained’ plots. Half the drained and undrained plots were direct‐drilled, and on the other half seedbeds were prepared by tillage to 200 mm. Tillage increased the total leaching loss of nitrate by 21 % compared with direct drilling in drained plots. About 95% or the nitrate moving from the soil was present in the water intercepted by the subsoil drains in these plots. In undrained plots less water and nitrate were collected in total; more of the nitrate was present in interflow on ploughed plots and in surface runoff in direct‐drilled land.

Losses of nitrate for the whole experiment from 1978‐1988 were analysed. This showed that, between the harvest of one crop and the spring application of fertilizer to the next, loss of nitrate‐N from ploughed land (Lp) was approximated by Lp=22+Fkg N ha−1, where F was the autumn fertilizer‐N applied. After fertilizer was applied in spring, loss of nitrate‐N depended on rainfall such that for 100 mm rainfall about 30% of the fertilizer‐N was lost by leaching. About 18% more nitrate‐N was lost from direct‐drilled land than from ploughed land in spring, but the total loss was generally small compared to that over winter.

The apparent net mineralization of organic‐N was measured in 1988. In autumn and winter there was little effect of tillage treatment (26 and 31 kg N ha−1 on direct drilled and tilled plots respectively). However, over the year 83 kg N ha−1 were mineralized in tilled plots, and 67 kg N ha−1 in direct‐drilled plots.

Five factors governing the leaching of nitrate are assessed and this identified that fertilizer nitrogen application to the seedbed of winter sown crops and the mineralization of nitrogen from the residues of the previous crop are the most significant factors for nitrogen leaching in the UK.
Effects of time and temperature on the bioavailability of Cd and Pb from sludge‐amended soils
Authors: HOODA P. S. , ALLOWAY B. J.
Published: July 2006

A pot experiment was conducted to compare the behaviour and bioavailability of Cd and Pb from two soils mixed with sewage sludge at three rates (0, 50 and 150 t ha−1) and maintained at two contrasting ambient temperatures (15°C and 25°C) over a period of one year following the treatments. Ryegrass (Lolium perenne) accumulated Cd and Pb in the sewage sludge treated soils, although accumulation was significantly lower in the soils treated at the high rate (150 t ha−1) compared to the low rate (50 t ha−1). Ryegrass grown in the warm environment (25°C) accumulated significantly higher levels of Cd and Pb than that grown in cooler conditions (15°C). Samples of the soils spiked with nitrate salts of Cd and Pb at equivalent rates of metal loading resulted in the ryegrass accumulating much higher levels of both the metals than on the sludge treated soils.

Metal uptake by the ryegrass from the sludge treatments increased over successive harvests while that from metal salt treatments decreased. The observed trend of increasing plant metal uptake over time coincided with a trend of decreasing pH in the sludge treatments. However, the concentrations of Cd and Pb extracted by DTPA failed to predict the changes in plant metal uptake. The importance of sewage sludge as both a source and a sink of pollutant metals and the trend of increasing bioavailability over time shown by this experiment are discussed.
The variation of critical‐state parameters with water content for two agricultural soils
Authors: PETERSEN C. T.
Published: July 2006

Triaxial tests were conducted on 436 reconstituted samples of two agricultural soils (a sandy loam and a loam) at moisture contents from air dryness to close to the respective liquid limits.

Volume‐change behaviour was largely consistent with the critical‐state concept, the role of soil‐moisture content being expressed in the values of the measured critical‐state parameters. The most important parameters, and their inherent variability, have been specified. Most of the parameters varied systematically with soil‐moisture content, but differently for the two soils. Some of the parameters were linearly correlated. The specific volume (v) was a linear function of the logarithm of the mean normal stress (In p) during normal compression and along the critical‐state line (CSL) with significantly different gradients (λ and λ*, respectively) at most moisture contents except close to the liquid limits. The standard errors of λ* were typically of the same magnitude as the gradients found during hydrostatic unloading from two different v‐levels whereas the standard errors of λ were up to a factor of ten smaller. The linear projections of the CSLs on the deviatoric stress (q)–mean normal stress plane showed intercepts on the q‐axis. Generally, precompaction leading to brittle failure had very little influence on the shear strength as compared with the strength in critical state.
Net mineralization, net nitrification and potentially available nitrogen in the subsoil beneath a cultivated crop and a permanent pasture
Authors: WEIER K. L. , MAcRAE I. C.
Published: July 2006

The brigalow clay soils of central Queensland in eastern Australia contain large quantities of nitrate‐N in the subsoil beneath shallow rooting cultivated crops. A laboratory incubation study was conducted to determine whether nitrate accumulation at depth beneath these crops was due to in situ nitrogen mineralization.

Intact soil cores, 5 cm long and 5 cm diameter, were obtained at four depths to 120 cm beneath cultivated black gram (Vigna mungo) and green panic (Panicum maximum var trichoglume) permanent pasture and incubated for 12 weeks at 60% water‐filled pore space and 25°C.

Net mineralization of organic N occurred in all soil cores obtained from under black gram with values ranging from 4.3 to 9 mg N kg−1 soil at 12 weeks. Beneath the pasture, net mineralization had not commenced by the end of 12 weeks.

Potentially available nitrogen (Na) ranged from 1.2 to 62.7 kg N ha−1 under black gram, and from 10.2 to 136.9 kg N ha−1 under pasture. A significant relationship was observed between Na and total N beneath both crops, and between Na and total C under the pasture.

Leaching of N mineralized in the surface layers of soil appears to be the main avenue of nitrate build‐up in the subsoil beneath black gram, with subsoil mineralization making only a partial contribution to the accumulated nitrate pool.
High energy ultraviolet photo‐oxidation: a novel technique for studying physically protected organic matter in clay‐ and silt‐sized aggregates
Authors: SKJEMSTAD J. O. , JANIK L. J. , HEAD M. J. , McCLURE S. G.
Published: July 2006

A novel approach to the study of organic‐matter distribution in soil microaggregates (<20 μm) using high‐energy ultraviolet (UV) radiation in the presence of oxygen (photo‐oxidation) is reported. The method quantitatively destroyed complex organic materials through oxidation, even in the presence of clay, provided the organic materials were directly exposed to the UV radiation.

Photo‐oxidation of clay and silt fractions for periods up to 8 h demonstrated that a considerable proportion of the organic matter was physically protected within clay‐ and silt‐sized aggregates. In some clay fractions, up to 23% of the organic carbon could be considered as physically protected whereas in silt fractions this was as high as 36%.

Infrared spectroscopy demonstrated that the materials external to both clay‐ and silt‐sized aggregates were largely proteinaecous in nature, while the materials in the interior of the aggregates resembled humic acids. These humic materials appeared to be physically shielded against photo‐oxidation, rather than being chemically recalcitrant. Using the clay‐ and silt‐sized fractions from one soil, 14C accelerator mass spectrometry demonstrated that, although both clay and silt fractions contained essentially modern carbon, after 4 h of photo‐oxidation much older organic carbon with a mean resonance time (MRT) of between 200±80 and 320±80 years before the present (BP) remained. This protection from photo‐oxidation, therefore, appears to mirror the process which physically protects organic substances in soils against microbial degradation. Photo‐oxidation of the clay‐plus‐silt fractions also resulted in a considerable reduction in particle size as the organic‐cementing agents, consisting of proteinaecous and humic materials, were oxidized.

Using data from the photo‐oxidation method along with infrared spectroscopy, radiocarbon dating and scanning electron microscopy, a simple model is proposed that spatially relates the various organic structures present to their positions in the mineral aggregates.
Fluorescence spectroscopy of aqueous pine litter extracts: effects of humification and aluminium complexation
Authors: TAM S.‐C. , SPOSITO G.
Published: July 2006

Fluorescence excitation, emission, and synchronous‐scan spectra were obtained for aqueous extracts of needle and litter layer (O‐horizon) samples from ponderosa pine collected at a plantation site. The spectral lineshapes differed markedly between the needle and litter samples, and showed an increasing overall intensity with increasing extent of humification (increasing depth in the litter layer). At a dissolved organic C (DOC) concentration of 100 g m−3, these effects were accompanied by a general shift in spectral density from lower to higher wavelength such that, in the excitation spectra, there was increasing prominence of a peak at 390 nm. When the DOC concentration was decreased from 100 to 25 g m−3, the overall spectral intensity decreased and the peak at 390 nm in the excitation spectra of the litter samples gave way to a rising peak at 340 nm. Changes in pH from 4 to 5, characteristic of the undiluted litter extracts, produced little effect on the spectra. The addition of A1 at 40 mmol m−3 generally produced enhancement of the fluorescence intensity in all three kinds of spectra for the needle and upper litter‐layer extracts at 100 g C m−3 and pH 4. Spectral density below 320 nm in the excitation and synchronous‐scan spectra of the needle solution (possibly attributable to gentisic acid on the basis of model experiments) was, however, diminished by Al addition. For the lower litter‐layer extracts, A1 addition decreased the fluorescence intensity in excitation and emission spectra, whereas it increased the intensity in synchronous‐scan spectra. These trends indicated that the water‐soluble fluorophores in the litter layer differed significantly from those in the fresh needles, and changed with the extent of humification. The 390‐nm peak in the excitation spectrum, particularly its behaviour in the presence of added Al, may be useful as a spectral signature of products formed by litter humification processes.
Nitrate leaching from grazed grassland lysimeters: effects of fertilizer input, field drainage, age of sward and patterns of weather
Authors: SCHOLEFIELD D. , TYSON K. C. , GARWOOD E. A. , ARMSTRONG A. C. , HAWKINS J. , STONE A. C.
Published: July 2006

Drained and undrained grassland lysimeter plots were established in 1982 on a clay loam of the Hallsworth series at a long‐term experimental site in south‐west England. The plots were continuously grazed by beef cattle, and received fertilizer at either 200 or 400 kg N ha‐1 per annum to the existing permanent sward, or at 400 kg N ha‐1 to a new sward, reseeded to perennial ryegrass following cultivation. Drainage water was monitored at V‐notch weirs and sampled daily for the analysis of nitrate‐N. Seven years of data are presented (five years for the reseeded swards). On the drained plots a large proportion of the rainfall was routed preferentially down large pores to the mole drains, whilst on the undrained plots, drainage was mainly by surface runoff. The average quantities of nitrate N leached per year were 38.5, 133.8 and 55.7 kg ha‐1 from the old sward that received 200 and 400 kg N ha‐1, and from the reseed that received 400 kg N ha‐1 fertilizer, respectively. Ploughing and reseeding resulted in a two‐fold reduction in leaching, except during the first winter after ploughing, and twice as much leaching occurred after a hot, dry summer as after a cool, wet one. Nitrate concentrations in drainage from either drained or undrained plots were rather insensitive to rainfall intensity, such that concentration was a good predictor of nitrate load for a given drainage volume. The drainage volume determined the proportion of the leachable N that remained in the soil after the winter drainage period. Initial (peak) concentrations of nitrate N ranged, on average, from 55 mg dm‐3 for the drained old sward that received 400 kg N ha‐1 fertilizer, to 12 mg dm‐3 for the undrained sward at 200 kg N ha‐1 fertilizer input. Concentrations of nitrate N in drainage from similar, unfertilized plots rarely exceeded 1 mg dm‐3. The results suggest that manipulating the nitrate supply can lessen leaching and that the route of water through soil to the watercourse determines the maximum nitrate concentration for a given load.
Changes in microbial biomass C, soil carbohydrate composition and aggregate stability induced by growth of selected crop and forage species under field conditions
Authors: HAYNES R. J. , FRANCIS G. S.
Published: July 2006

The effects of growth of various crop and forage species on microbial biomass C, soil carbohydrate content and monosaccharide composition, and mean weight diameter (MWD) were investigated in two field experiments. One experiment was conducted over one growing season (4 months) whereas the other had been conducted for three consecutive growing seasons (32 months). In the four‐month experiment, aggregate stability (estimated as MWD) of soil from experimental plots followed the order Italian ryegrass > prairie grass > phacelia = pea = maize. At the 32‐month site the order was perennial ryegrass > annual ryegrass > perennial white clover = barley. At both sites crops with the greatest root mass and root length density had the greatest effect on increasing MWD. In all cases, rhizosphere soil had a significantly higher microbial biomass and MWD than non‐rhizosphere soil. However, organic C, total content of acid‐hydrolysable carbohydrate and content of individual monosaccharides in acid hydrolysates were similar in rhizosphere and non‐rhizosphere soil.

The fraction of soil carbohydrate extractable with hot water (representing about 6‐8% of the total carbohydrate content) was significantly higher in the rhizosphere soil. This fraction has a galactose plus mannose over arabinose plus xylose ratio of 2.1–2.3 indicating that it was predominantly of microbial origin. It is suggested that the carbohydrate fraction extractable with hot water is made up of exocellular microbial polysaccharides that are involved in stabilizing soil aggregates in the rhizosphere. By comparison with arable crop species, grass species have a larger root mass and root length density, and therefore a higher microbial biomass and larger production of carbohydrate extractable with hot water. As a result they have a more marked effect on improving soil aggregate stability.
Water uptake by aggregates
Authors: YOUNGS E. C. , LEEDS‐HARRISON P. B. , GARNETT R. S.
Published: July 2006

The Green & Ampt infiltration analysis is applied to the problem of the water uptake by aggregates when they are surrounded by water. Two situations are analysed, namely, when there is free escape of the displaced air and when there is no escape of the air. These extreme situations provide bounds for estimating the water uptake for the practical case when some air escapes through the aggregate's surface in the form of bubbles as the aggregate wets up. It is shown that the rate of water uptake is directly proportional to the square of the sorptivity of the aggregate material and inversely proportional to the square of the final water uptake. Experiments on spherical stabilized clay aggregates of different radii were in agreement with the theoretical analysis that predicted the observed very rapid wetting up. The analysis also showed that when there was free escape of air, the rate of advance of the wetting front into cylindrical and spherical aggregates decreased from an initially infinite value to a minimum value and then increased to an infinitely large value when the front reached the centre of the aggregate, in contrast to the continually decreasing rate into plate‐like aggregates. This was demonstrated in experiments on the radial water movement into a fine sand contained in a cone.

The analysis and experimental results indicate that preferential macropore flow in aggregated soils can be initiated very rapidly when air entrapment occurs within the aggregates.
The self‐diffusion of strongly adsorbed anions in soil: a two‐path model to simulate restricted access to exchange sites
Authors: NYE P. H. , STAUNTON S.
Published: July 2006

The consequences of slow diffusion of strongly adsorbed solutes into soil aggregates are not fully understood. The distribution of 32P after diffusing down a soil column cannot be explained from a consideration of liquid‐phase impedance factor and isotopic exchange alone, as can that of 36CI.

A model was developed that considers the soil to provide linked parallel intra‐aggregate and inter‐aggregate pathways. With this geometry, simulations agreed fairly well with experimental data when the intra‐aggregate impedance factor was 0.001, using other model parameters that had been determined in independent equilibration studies. With this intra‐aggregate impedance factor, the model yielded straight‐line plots for chloride and the overall impedance factor derived agreed closely with the experimental one. The intra‐aggregate impedance factor for 32P also agreed with the rate of reaction of the rapidly‐exchanging P fraction previously determined. The slowly‐exchanging P fraction has little influence on the P concentration profiles up to 10 d, but the small exchanged amount does have an effect at run times of 57 d.

The slow intra‐aggregate diffusion of strongly adsorbed solutes decreases the amount adsorbed from a surface source of supply, and it also decreases the amount that is taken up by a surface sink. However, the interaggregate solution concentration remote from a source of supply is considerably increased, which may be important if the solute is a pollutant or a nutrient.
Critical state parameters derived from constant cell volume triaxial tests
Authors: O'SULLIVAN M.F. , CAMPBELL D.J. , HETTIARATCHI D.R.P.
Published: July 2006

Critical state parameters were determined in constant cell volume triaxial tests on three remoulded agricultural topsoils, a sandy loam, a clay loam and a clay. Tests were made at a range of water contents. The normal consolidation lines tended to be linear on a semi‐logarithmic plot up to a degree of saturation of c. 0.85, above which the soil was incompressible but highly deformable. The slopes of the projected critical state lines were slightly greater than the slopes of the normal consolidation lines for all three soils. For each soil, both lines pivoted about a point as water content increased and, for the two lighter‐textured soils, the increases in compactibility tended to be greatest near the plastic limit. For all three soils, strength remained fairly constant with increasing water content until the soil was at around 70‐85% of the cone penetrometer plastic limit. Strength then decreased with increasing water content, with the smallest decrease in the sandy loam.
Evaluating soil maps for prediction of soil water properties
Authors: LEENHARDT D. , VOLTZ M. , BORNAND M. , WEBSTER R.
Published: July 2006

Conventional soil survey stratifies a region into mapping classes and characterizes each by a representative soil profile within it. The efficacy of the procedure for predicting particle‐size fractions, bulk density, water retention, and available water capacity (AWC) of the soil at previously unvisited sites on the Plain of Languedoc in southern France is evaluated for three scales of survey (1/10 000, 1/25 000 and 1/100 000) and is compared to that of prediction from stratified random and simple random samples. Data from 85 soil profiles on a random transect were used for evaluation.

Classification partitioned the variation of the measured properties, except for AWC, well at the 1/10 000 and 1/25 000 scales, whereas classification at the 1/100 000 scale was less effective. At the 1/10 000 and 1/25 000 scales both classification and stratified random sampling were better for prediction than simple random sampling for the same total sample. On average the representative profiles proved substantially better predictors than the stratified random samples, but in most situations where soil stratification performed well efficiencies of the two predictors were similar. In essence, the more successful the classification was the more difficult it was to improve prediction by selecting representatives instead of sampling randomly within classes. These results confirmed statistically that the soil surveyor can exercise intuition and judgement to classify and select representatives.
Conservation of mineral nitrogen in restored soils at opencast coal mine sites: II. The effects of inhibition of nitrification and organic amendments on nitrogen losses and soil microbial biomass
Authors: WILLIAMSON J.C. , JOHNSON D.B.
Published: July 2006

Soils stored in stockpiles during opencast mining operations accumulate significant quantities of ammonium (of the order of 200 μg NH4+‐N g−1 soil) within the predominantly anaerobic cores of mounds. Upon stockpile dismantling and land restoration, this NH+4‐N is rapidly oxidized to NO−3‐N, which is readily lost from newly restored soil ecosystems by leaching and denitrification. Experiments were set up to examine how these significant reserves of mineral N might be conserved in such situations. Application of the nitrification inhibitor dicyandiamide was successful in minimizing NO3−‐N lost by leaching, though large concentrations of NH4+‐N were detected in drainage waters. Straw incorporation decreased nitrate leaching by up to 40%; biomass C was some 40% greater in straw‐amended than in unamended soils after 14 weeks, though biomass N was similar in both. Addition of nitrogen‐free organic materials (glucose, starch and cellulose) produced different results, with glucose amendment showing the greatest reduction in nitrate leaching in the short term (due to an apparent stimulation of denitrification) whereas addition of cellulose resulted in the most effective conservation of nitrogen over 14 weeks; this was due, at least in part, to uptake of mineral N by the soil microbial biomass.
Influence of soil properties on the response to phosphorus in some tropical soils: I. Initial response to fertilizer
Authors: WARREN G.P.
Published: July 2006

The availability of fertilizer P in six P‐deficient tropical soils from Brazil, Kenya, Malaysia and Indonesia was assessed by grass in a pot experiment. Grass dry matter yield (D) and fertilizer P(F) were fitted to a Mitscherlich equation: D= a−b exp(−cF), and P uptake (U) and F to the linear equation: U=α+βF. Fitted parameter β equals the proportion of P recovered in one crop and it varied widely between soils, ranging from 12 to 51%. Quantitative assessments of fertilizer‐P availability could also be made using dry‐matter data alone if the rates of fertilizer used were well distributed along the response curve, when Mitscherlich parameter c was correlated well with β.

Chemical measurements were made on uncropped soil. Phosphate sorption isotherms were measured, using 32P to assess exchangeable and non‐exchangeable phosphate. The availability parameters c and β were correlated best with parameter be, the phosphate buffer capacity derived from the fitted Freundlich isotherm for exchangeable phosphate, suggesting that the mobility of exchangeable phosphate is a major influence on P availability. Al and Fe were extracted with acid oxalate, citrate‐dithionite and pyrophosphate reagents, and parameters c and β correlated best with Al extracted by acid oxalate. These relationships were inverse, showing that Al in disordered mineral forms lowers the availability of fertilizer P.
Adsorption of radiocaesium on various soils: consequences of the effects of soil: solution composition on the distribution coefficient
Authors: STAUNTON S.
Published: July 2006

The adsorption of a radioisotope of caesium, 137Cs, has been interpretation and ratio and solution measured on four soils with differing clay mineralogies. All measurements have been made using unwashed soils in suspensions shaken for 2 h at 20°C. The effects of concentration in potassium and caesium, the nature of the background electrolyte and the soil:solution ratio have been investigated. The results are expressed either as the distribution coefficient, KD or as Freundlich isotherms.

The distribution coefficient of each of the soils decreases markedly as the concentration of caesium increases. The adsorption properties of the soils are not determined by the dominant clay mineralogy alone. Adsorption is always lower in 0.01 m CaCl2 solution than in water. The addition of potassium has relatively little effect on adsorption of trace amounts of caesium; however, KD decreases with increasing concentrations of stable caesium. The major reason for the dependence of KD on the soil: solution ratio is found to be the non‐linear adsorption isotherm; the influence of the varying compositions of the solution and exchange complex is minor.

The validity of the use of a single KD value as an indicator of adsorption capacity and the meaning of the relative values of the Freundlich parameters are considered. The implications of these findings for the use of radiotracers and the usefulness of KD as an indicator of bioavailability are discussed.
Ionic‐strength and pH effects on the sorption of cadmium and the surface charge of soils
Authors: NAIDU R. , BOLAN N.S. , KOOKANA R. S. , TILLER K.G.
Published: July 2006

Two Oxisols (Mena and Malanda), a Xeralf and a Xerert from Australia and an Andept (Patua) and a Fragiaqualf (Tokomaru) from New Zealand were used to examine the effect of pH and ionic strength on the surface charge of soil and sorption of cadmium. Adsorption of Cd was measured using water, 0.01 mol dmp−3 Ca(NO3)2, and various concentrations of NaNO3 (0.01–1.5 mol dm−3) as background solutions at a range of pH values (3–8).

In all soils, the net surface charge decreased with an increase in pH. The pH at which the net surface charge was zero (point of net zero charge, PZC) differed between the soils. The PZC was higher for soils dominated by variable‐charge components (Oxisols and Andept) than soils dominated by permanent charge (Xeralf, Xerert and Fragiaqualf). For all soils, the adsorption of Cd increased with an increase in pH and most of the variation in adsorption with pH was explained by the variation in negative surface charge. The effect of ionic strength on Cd adsorption varied between the soils and with the pH. In Oxisols, which are dominated by variable‐charge components, there was a characteristic pH below which increasing ionic strength of NaNO3 increased Cd adsorption and above which the reverse occurred. In all the soils in the normal pH range (i.e. pH>PZC), the adsorption of Cd always decreased with an increase in ionic strength irrespective of pH. If increasing ionic strength decreases cation adsorption, then the potential in the plane of adsorption is negative. Also, if increasing ionic strength increases adsorption below the PZC, then the potential in the plane of adsorption must be positive. These observations suggest that, depending upon the pH and PZC, Cd is adsorbed when potential in the plane of adsorption is either positive or negative providing evidence for both specific and non‐specific adsorption of Cd. Adsorption of Cd was approximately doubled when Na rather than Ca was used as the index cation.
Simulating diffusion in a Boolean model of soil pores
Authors: HORGAN G.W. , BALL B.C.
Published: July 2006

The diffusion of gas through a model of the structure of soil pores was simulated on a computer. This was done to test the model's usefulness for studying diffusion in real soil and to obtain insights into how soil pore geometry affects diffusion. A model of randomly‐placed overlapping spheres was used to represent the soil solids, the pores being what remains. Various simulated porosities and average sphere radii produced pore networks which resembled those in real soil aggregates. Our diffusion simulations gave three results: steady‐state flux, time delay and rate of increase of flux. The porosity and sphere size were varied to investigate their effects on these diffusion properties. Results were comparable with those from experimental work. Further analysis allowed us to express the geometry of pore simulations in terms of average pore path length and connectivity. Evidence of non‐Fickian behaviour was obtained, particularly in the early stages of the simulated diffusion.
AN INTERNATIONAL EXPERIMENT ON THE EFFECT OF AGE AND STORAGE CONDITIONS ON VIABILITY AND DORMANCY OF AVENA FATUA SEEDS
Authors: THURSTON J. M.
Published: July 2006

Summary. Freshly collected ripe seeds of Avena fatua were first kept out of doors on the surface of the soil for 0 to 3 monehs, and then stored dry in the laboratory for 0 to 6 months before testing for dormancy and viability. Results from six European countries agreed well. Only 10% of ripe seeds germinated immediately alter collection and germination rose to 50% by December or January in all countries except Denmark. Viability was scarcely affected by age or storage conditions, except that many seeds died out of doors during winter in Denmark and Germany. The percentage of dormant seeds in December was greater in Denmark than elsewhere, possibly because the seeds were of a different type. Seeds may not behave the same in normal agricultural conditions as they did in this experiment.

Une expérience internationale sur l'influence de l'âge et des conditions de conservation sur la viabilité et la dormance de semences d'Avena fatua
HERBICIDE PRACTICE IN ARABLE FARMING DISTRICTS OF EASTERN ENGLAND, 1959‐60
Authors: CHURCH B. M. , DADD C. V. T. , MILLER T. K. , PAGE J. B.
Published: July 2006

Summary. Information on the use of herbicides in the 1959‐60 crop year was collected from a stratified random sample of farms in each of four arable farming districts in Eastern England.

In each of the surveyed districts about 80% or more of the area under cereals, 10‐20% of other tillage crops and about 10% of the grassland was treated with herbicides. In the three diatricts where peas were widely grown most of this crop was also treated. Contract services were used most on the smaller farms.

MCPA was the most widely used herbicide on cereals, but in two of the four districts mecoprop was also often used. Manufacturer's reeommendations for rates of application were followed fairly closely for MCPA on cereal crops which were not undersown but MCPA was also used on much of the undersown cereals in spite of the risk of damage to the legumes. MCPB and mecoprop were often applied to cereals at rather lower rates than those generally recommended, Little detailed information was obtained about when herbicides were applied but clearly most farmers were influenced more by general crop appearance (and possibly date) than by the stage of growth of crop or weeds.

The weeds most often mentioned by farmers as occurring on areas treated with herbicide were Cirsium spp., Sinapis arvensis. Galium aparine, Stellaria media, Chenopodium album and Rumex spp. The weeds which were most frequently difficult to control were Avena spp.Polygonum persicaria, Tussilago farfara, Stellaria media and Matricaria maritima ssp. inodora. The herbicides used were usually appropriate for the weeds which they were intended to control and nine out of every ten farmers asked were satistified with the results of treatment; it was very rare for any detrimental effect on crops to have been noted.

L'emploi d'herbicides dans quatre régions agricoles de l'est de l'Angleterre 1959‐60
THE EFFECT OF COMPETITION FROM CEREAL CROPS ON THE GERMINATION AND GROWTH OF AVENA FATUA L. IN A NATURALLY‐INFESTED FIELD
Authors: THURSTON JOAN M.
Published: July 2006

Summary. The effect of winter wheat, winter rye, winter barley, spring barley, and fallow cultivated as for a winter cereal, on germination and growth of wild oats (A. fatua) was investigated on a naturally‐infested field. Treatments were continued for 2 years on the same plots and in the third year all plots were cropped with spring barley. Wild oats were not allowed to shed seeds.

A. fatua was controlled by a dense crop of an autumn‐sown cereal. The crop genus was unimportant provided it grew well on the site; its effectiveness depended on its density when the wild oats germinated in spring. Winter wheat and winter rye were equally effective. Even in a light crop of barley, wild oats grew much less vigorously than on the fallow plots. Beyond a certain crop density dependent on soil fertility, further increase in crop did not decrease the size of wild oats. The heaviest crop did not completely suppress the wild oats.

The crop affected the wild oats mainly by decreasing growth of the seedlings, but under winter wheat and winter rye some wild oat seeds may have remained dormant, germinating in the spring barley in the third year, perhaps because the crops decreased the soil moisture content. Nitrogenous fertilizer increased the weight of both crops and wild oats. Barley was more severely affected by soil acidity than wild oats and on acid areas of barley plots the wild oats were larger than where the pH was higher. In wheat and rye which were scarcely affected by soil acidity the size of the wild oat plants was unaffected by soil pH.

L'effet du competition des céréales sur la germination et le développement d'Avena fatua dans un champ naturellement infesté.
HERBICIDES AS FERTILIZER ADDITIVES
Authors: SCOTT M. R. , SCOTT E. M.
Published: July 2006

Summary. Granulated compound fertilizers were tested as solid carriers for a variety of herbicides known to be active when applied as liquids.

Pasture and cereal experiments with 2,4‐D and MCPA as fertilizer additives indicated considerable loss of herbicidal activity in comparison with spray formulations.

Residual herbicides such as TCA, propham and diuron retained their activity when added to fertilizer for application to root crops. The most effective of the herbicides used as fertilizer additives were TCA and propham, both of which gave good control of Avena fatua in sugar beet, and a mixture of chlorpropham and diuron gave promising results as a general weed control treatment in carrots.

It is concluded that the addition of these or similar herbicides to fertilizer granules may have advantages over conventional spray formulations for those crops which require broadcast pre‐sowing applications of herbicides and fertilizer. For such crops the use of a granular fertilizer as the carrier instead of inert material could also have advantages over conventional granular herbicides, particularly by reducing transport and application costs.
THE FATE OF N‐(4‐CHLOROPHENOXY)‐PHENYL‐NN‐DIMETHYLUREA (C‐1983) IN SOILS AND PLANTS*
Authors: GEISSBÜHLER H. , HASELBACH G. , AEBI H.
Published: July 2006

Summary. The adsorption of N'‐(4‐chlorophenoxy)‐phcnyl‐NN‐dimethylurea (C‐1983) and N‐butyl‐N‐(3,4‐dichlorophenyl)‐ N‐methylurea (ref. comp.) by different soils was investigated with a slurry‐type procedure. Freundlich isothermal equilibrium plots demonstrate that both herbicides, but especially C‐1983, were quite strongly adsorbed, on soil particles. The following concentrations of C‐1983 adsorbed were found to be in equilibrium with 1 ppm soil solutions: 14 γ/g (sandy loam), 40 γ/g (clay loam) and 110 γ/g (humus soil) The corresponding values for the ref. comp. were 6.3, 21 and 60 γ/g. Adsorption of C‐1983 was strong on bentonite (400 γ/g) and less pronounced on cellulose (48 γ/g). Soil pH had no significant effect on adsorption. Desorption equilibrium plots indicate that about 50% of C‐1983 adsorbed was released into solution according to adsorption equilibrium conditions. The remaining 50% came off at a much lower rate.

Leaching of C‐1983 and the ref. comp. was studied with soil columns to which 200 mm of simulated rain was applied during a period of 45 hours. At a low soil moisture level (wilting capacity), the bulk of C‐1983 was not removed from the top 1 cm section of all three soils. Leaching was somewhat more pronounced in sandy loam (80% recovery in top 1 cm layer) than in clay loam (90%) or in humus soil (95%). Only traces of C‐1983 were recovered from depths below 10 cm and in water percolating from the columns. The ref. comp. leached more easily than C‐1983, especially in sandy loam (bulk of herbicide below 5 cm level). Leaching of both herbicides, but especially of the ref. comp., was less pronounced at the higher soil moisture level (field capacity wet) than at the lower one (wilting capacity).

It is suggested that leaching is not a major factor in removing C‐1983 from the surface soil layers. On the other hand, its very strong adsorption seems to be a decisive factor in controlling its availability insoil solution and thus determining both the initial toxicity and and the residual activity in some types of soils. The practical implications for field use are discussed.

Le comportement de la N'‐(4‐chllorophénoxy)‐phényl‐NN‐diméthylurée (C‐1983) dans les terres et dans les plantes 1. Adsorption et lessivage dans divers types de terres
EVALUATION OF PARAQUAT AND DIQUAT FOR WEED CONTROL IN RUBBER
Authors: JEATER R. S. L.
Published: July 2006

Summary. In Malayan rubber plantations where the weed flora was dominated by grasses paraquat was superior to diquat as a herbicide. At the rates needed to give satisfactory grass weed control paraquat also gave an adequate control of broad‐leaved weeds.

The rate of paraquat needed varied between 0.75 and 1.25 lb/ac depending on the weed flora and the growth stage of the rubber trees. In young rubber 1.0–1.25 lb/ac gave 8–10 weeks' control, but in mature rubber there was only 20% recovery 6 months after an application of 0.75 lb/ac. Where weed regrowth was very rapid after the initial spray, as in the case of Paspalum conjugation in young rubber, a second application some 2–3 weeks after the first was an advantage. The volume of water in which it was applied was not critical.

Rain falling soon after application did not reduce the herbicidal activity of paraquat. Paraquat did not injure rubber trees providing it was not sprayed onto green tissue and this feature combined with its inactivation by soil made it safe to use from a very early stage in the growth of the rubber trees.

L'évaluation du paraquat et du diquat pour la lutte contre les mauvaises herbes dans les plantations de caoutchouc
PHYTOTOXICITY OF HERBICIDES AS MEASURED BY ROOT ABSORPTION*
Authors: HILTON H. W. , NOMURA N.
Published: July 2006

Summary. The phytotoxicity of numerous herbicides was measured on cucumber, sorghum, and wheat plants in terms of the minimum lethal concentration of herbicide in nutrient solution surrounding the roots of photosynthetizing plants. Wheat and cucumber were about equally sensitive as test plants, while, sorghum at a similar growth stage required ten to one hundred times the concentration (on a molar basis) of most chemicals for lethal effect. Only paraquat as a root‐absorbed herbicide appeared to be completely non‐selective to all three species. The triazines showed considerable selectivity to sorghum; of all the triazines tested only CP‐17029 was more toxic to wheat and sorghum than to cucumber.

None of the compounds were ethal at a concentration of 10−7 molar (7.00, expressed as the negative logarithm); the triazine G‐34360 (desmetryne) showed the greatest toxicity (6.85) to the cucumber plant. Diuron on the same species had a toxicity rating of 6.69 and bromacil 6.72.

Mesure de la phytotoxicité des herbicides au moyen de l'absorption radiculaire