bluuebunny/crossref_metadata_2025 huggingface dataset:
THE NATURE OF THE NITROGEN COMPOUNDS IN SOIL ORGANIC MATTER EXTRACTED BY ANHYDROUS FORMIC ACID
Authors: JONES M. J. , PARSONS J. W.
Published: July 2006

Organic matter extracted with 9 : 1 formic acid : acetylacetone from twenty‐five soils of widely varying organic content and precipitated with excess di‐isopropyl ether was hydrolysed with 6N HC1. The relationships between the proportions of acid‐soluble N, acid‐insoluble N, amino‐N, and ammonium‐N thus produced, and the properties of the original soil were examined. The distribution of N in acid hydrolysates was similar to that reported in the literature for material isolated by neutral and alkaline extractants. The relatively large proportion of N released as ammonium‐N from organic matter obtained from soils of high pH and low C : N ratio may derive from organically fixed ammonia. The low levels of amino‐N in organic matter extracted by formic acid from soils of high clay content imply the existence of clay‐amino complexes that resist extraction although formation of such complexes during extraction cannot be ruled out.
THE MEASUREMENT AND PREDICTION OF AVAILABLE WATER CAPACITY OF FERRALLITIC SOILS IN UGANDA
Authors: PIDGEON J. D.
Published: July 2006

Field capacity was measured directly, and soil moisture characteristics were determined on undisturbed cores, for a wide textural range of ferrallitic soils in Uganda. The initial moisture conditions of the soils were shown to affect results and thus standardized procedures were adopted for field and laboratory determinations. Laboratory estimates of field capacity for undisturbed and disturbed samples were shown to be unreliable, but a correction factor was found which improved them. There was no single moisture tension for undisturbed core samples that corresponded to field capacity.

Particle‐size composition could be related to field capacity, permanent wilting‐point, and available water capacity by multiple regression equations having correlation coefficients of 0.96, 0.98, and 0.88 respectively. The relationships predicting available water capacity were different from those found for soils in England, but those for field capacity and permanent wilting‐point were similar. Particle‐size analyses were carried out using three methods of dispersion of different efficiencies. Particle‐size composition following gentle dispersion by shaking soil with distilled water was poorly correlated with moisture‐holding properties. There was little advantage in using vigorous ultrasonic dispersion compared with overnight shaking with sodium hexametaphosphate.

Two soils formed on alluvial deposits with kaolinite the only clay mineral, and one soil with montmorillonite the dominant clay mineral, showed markedly different relationships between moisture‐holding properties and particle‐size composition.
THE ALKALINITY OF ALKALI SOILS
Authors: VAN BEEK C. G. E. M. , VAN BREEMEN N.
Published: July 2006

The theoretically derived equation: log Alk–pH = log Pco2–7.82 describes the relation between three easily estimated parameters, viz. the composition (alkalinity), CO, partial pressure and the pH of the soil solution. This equation is also important for understanding the formation of alkaline soils. The concept of residual alkalinity, i.e. the difference between the alkalinity and the total concentration of the divalent cations in the soil solution (on an equivalent basis) is introduced. In a closed basin with excess evaporation over precipitation highly alkaline soils, i.e. soils with a pH above 8 to 8.5, develop if the inflowing water has a positive residual alkalinity. A number of processes, such as weathering, oxidation and reduction, cation exchange, precipitation, addition of neutral salts, evaporation, which may influence the alkalinity and residual alkalinity of natural waters and soils are discussed briefly.
OBSERVATIONS ON THE SOIL‐WATER REGIMES IN A DRAINED CLAY SOIL
Authors: TRAFFORD B. D. , RYCROFT D. W.
Published: July 2006

Details of soil‐water profiles between drains and the associated drain‐flow data are presented for the winter period on a clay soil of the Ragdale series, formed in drift over Lias clay in the Midlands of England. A conventional water‐table is shown to exist and the rate of drain flow is shown to depend on whether the water‐table is high enough to be within layers having a better hydraulic conductivity than the normal subsoil. Mole drainage is shown to modify the drainage performance considerably by providing a quicker disposal of water, and significantly lower water‐table subject to much smaller fluctuations in level. Where drains have been laid in the natural subsoil, without this being disturbed by deep cultivations, the water‐table level is frequently close to cultivation level and there appears to be little water movement in the subsoil. It is concluded that for effective drainage, soils of this type require deep cultivations to modify the subsoil and allow water movement at greater depth.
A MODEL FOR PREDICTING THE REDISTRIBUTION OF SALTS APPLIED TO FALLOW SOILS AFTER EXCESS RAINFALL OR EVAPORATION
Authors: BURNS I. G.
Published: July 2006

A model is described for predicting the movement of soluble unadsorbed anions (such as nitrate or chloride) in fallow freely drained soil under field conditions. The model includes routines for estimating both the downward leaching of salts (after excess rainfall or irrigation) and the capillary movement of anions to the soil surface (after evaporation). The profile is divided into layers each of which is characterized by a maximum and minimum water content (the field capacity and evaporation limit respectively). Daily amounts of rainfall and evaporation are applied to the surface and the redistribution of water and salts is calculated (on a layer‐to‐layer basis) from the initial water and salt contents of each layer by adding or subtracting water to or from the moisture content until the stated maximum or minimum value is reached. Salt transfer is calculated from the amount af water movement on a proportional basis. The predictions of the model have been tested using field data for the redistribution of nitrate and chloride in a sandy loam soil. Good agreement was obtained for chloride, but the results for nitrate showed some deviations probably due to the effects of denitrification.
FIXED AMMONIUM IN NIGERIAN SOILS I. SELECTION OF A METHOD AND AMOUNTS OF NATIVE FIXED AMMONIUM
Authors: OPUWARIBO E. , ODU C. T. I.
Published: July 2006

Three of the common methods for the determination of native fixed ammonium in soils‐the Rodrigues modified, the Bremner KOH method, and the Silva Bremner method‐were evaluated and the Silva‐Bremner method was chosen. Native fixed ammonium in 212 profile samples representing different soil types and sampling localities in Nigeria was found to range from 4 to 98 ppm. Fixed ammonium accounted for 1‐7 per cent of total nitrogen in surface soils and 3‐48 per cent in the sub‐soils. More than half of the values fell within the ranges 2‐4 and 8‐20 per cent respectively. The results do not agree with the high values reported earlier for four Nigerian soil profiles.

Fixed ammonium, both in absolute amounts and as a percentage of total nitrogen, increased with depth in most profiles though maximum amounts were not necessarily attained in the lowest horizons. Fixed ammonium values were lower in soils derived from sandy parent material than in those derived fromigneous or metamorphic rock and were generally less in the more humid southern parts of the country than in the drier north. Fixed ammonium, especially in subsoils, contributes to the nitrogen economy in these soils.
DISPLACEMENT OF AMMONIUM IONS FOR CATION EXCHANGE CAPACITY MEASUREMENTS
Authors: TUCKER B. M.
Published: July 2006

The best reagent for displacing adsorbed NH, for the measurement of cation exchange capacity of soils is a mixed ZN nitrate solution of potassium and calcium. The equivalent ratio of K to Ca should be in the range from 1 to 3. This mixture is better than simple solutions of Li, Na, K, Mg, Ca, Sr, and Ba nitrates and mixtures of KNO3 with any one or two of these other nitrates.
FORMATION OF IRON OXIDES BY DECOMPOSITION OF IRON‐PHENOLIC CHELATES
Authors: McHARDY W. J. , THOMSON A. P. , GOODMAN B. A.
Published: July 2006

Iron chelates of some simple di‐and trihydric phenols can be decomposed by peroxide treatment or by hydrolysis to yield crystalline ferric oxides. The species of ferric oxide obtained depends upon the precipitating conditions and the nature of the chelating ligand. In oxidative virtually anion‐free conditions, decomposition of all aged chelates yields a precipitate of disordered ferric oxide, which is referred to as‘protohaematite’, since it ages to haematite in water even at room temperature. Protohaematite is considered to be a discrete form of ferric oxide similar in structure to δ‐FeOOH but devoid of hydroxyl groups and may be present in freely drained soils as a precursor of haematite. Hydrolysis of all unaged chelates, except that of iron protocatechuic acid, yields lepidocrocite. The redox cycle undergone by iron in this reaction may be analogous to one prevailing in gley soils. In the presence of montmorillonite, the iron‐catechol system forms a clay‐metal‐organic complex, which also decomposes to yield lepidocrocite provided chloride ions are present on the clay surface. The fact that various inorganic gels amorphous to X‐rays can also deplete the ligand content of the chelates indicates a possible inorganic decomposition mechanism for metal‐organic chelates in soils.
DISSOLUTION KINETICS OF SILICATE MINERALS IN AQUEOUS CATECHOL SOLUTIONS
Authors: JØRGENSEN S. STORGAARD
Published: July 2006

Fine particle samples of silicate minerals and of gibbsite were shaken with solutions of pyrocatechol, 4‐nitro‐pyrocatechol or 3,4‐dihydroxybenzoic acid at pH 9·3–9·7 and 25°C. In 63 days, from 1·4 per cent (illite) to 17·9 per cent (nepheline) of the silica present was dissolved. Except for kaolinite in solutions of the two substituted catechols, the aluminosilicates dissolved incongruently, leaving residues enriched with aluminium.

When accumulated amounts of elements (Si, Al, Na, K) dissolved from nepheline were plotted against time on log‐log paper straight lines were obtained. For quartz, kaolinite, and in some cases gibbsite similar plots could be approximated by two straight‐line segments. The plots for microcline and oligoclase may be described by a combination of three‐line segments. Several possible reaction mechanisms are discussed but a mechanism which explains the similar rate profiles has not yet been formulated.
CHEMICAL AND MINERALOGICAL PROPERTIES OF BROWN PODZOLIC SOILS IN COMPARISON WITH SOILS OF OTHER GROUPS
Authors: LOVELAND P. J. , BULLOCK P.
Published: July 2006

Chemical and mineralogical properties of brown podzolic soils, brown earths, a podzol, and an Andept have been studied with particular reference to the kinds and distribution of amorphous materials.

In addition to pyrophosphate extractable (Fe + Al)/per cent clay, brown podzolic soils can be distinguished from brown earths by Fe‐oxalate/Fe‐dithionite and Fe‐pyrophosphate/Fe‐dithionite ratios, fluoride reactivity, and the presence of intergrade 2:1‐2:2 and smectite‐like clay minerals in surface horizons.

Significant amounts of amorphous alumino‐silicates resembling allophane were found in the Bs horizons of the brown podzolic soils, particularly those on igneous rocks. These amounts are sufficiently large to suggest the recognition of an Andic sub‐group of brown podzolic soils in England and Wales.
ADSORPTION ON HYDROUS OXIDES. IV. MECHANISMS OF ADSORPTION OF VARIOUS IONS ON GOETHITE
Authors: PARFITT R. L. , RUSSELL J. D.
Published: July 2006

Infrared spectroscopy has been used to investigate the complexes that are formed when acids are evaporated onto goethite. It is probable that, like HPO2−4, the anions SO2−4, SeO2−3, and oxalate are adsorbed by ligand exchange and form binuclear bridging complexes where two singly coordinated A‐type OH groups are replaced by two oxygen atoms of one ligand. There is evidence that HPO2−4 and oxalate are likely to be present in this form in wet environments, and this is probably also true for SO2−4 and SeO2−3.

Fluoride ions can completely replace the singly coordinated A‐type OH groups but do not replace C‐ or B‐type OH groups that are coordinated, respectively, to two and three Fe3+ ions. The other halides, nitrate, and benzoate partially replace the A‐type OH groups, benzoate being adsorbed as a monodentate ligand.

Copper ions do not appear to react with A‐type OH but zinc ions are probably adsorbed on the goethite (100) face in conjunction with carbonate or bicarbonate.
REACTIONS OF SOLUBLE PHOSPHATE WITH ACID SOILS: THE INTERPRETATION OF ADSORPTION‐DESORPTION ISOTHERMS
Authors: WHITE R. E. , TAYLOR A. W.
Published: July 2006

Adsorption‐desorption and isotopic‐exchange isotherms for acids soils of known clay mineralogy indicated that when all the surfaœ P accessible to the solution was considered, the bonding energy for phosphate decreased exponentially with site coverage. The soils differed markedly in the quantities of surface P held at sites of very high bonding energy, defined as those in equilibrium with a solution concentration < 1 μM; the values ranging from 9 μmol g−1 in a soil with 40 per cent gibbsite in the clay fraction, to 1 μmol g−1 in a soil with only 1 per cent gibbsite and no interlayered material.

The reversibility of current P adsorption on soil surfaces depended on the immediate history of the soil sample. Complete reversibility occurred when soil, previously enriched with soluble P and stored for 4 to 5 months at constant temperature, was suspended in solutions of constant pH and ionic strength. It is suggested that irreversibility occurs due to incomplete attainment of equilibrium during the adsorption phase, a condition predisposed by high initial P concentrations (>1mM), and the use of soils that are naturally in dis‐equilibrium because of recent fertilizer additions or severe depletion of P by plant uptake.
MEASUREMENT OF PORE SIZES IN FINE‐TEXTURED SOILS: A REVIEW OF EXISTING TECHNIQUES
Authors: LAWRENCE G. P.
Published: July 2006

Pore size distributions obtained from the relationship between moisture content and suction are not dependable in fine‐textured soils because of shrinkage. To overcome this problem, methods such as nitrogen sorption, mercury intrusion porosimetry, non‐polar liquid desorption and thin sectioning have been used. In order to pre‐dry samples without changes in the pore system, freeze‐drying, organic liquid replacement of soil water, and critical point drying techniques have been employed. These methods of soil drying and pore size measurement are described and compared, and the validity of their use in soil studies is examined. The measurement of pore sizes by water desorption is also discussed.
ADSORPTION OF CADMIUM AND ITS EXCHANGE CHARACTERISTICS IN SOME ISRAELI SOILS
Authors: NAVROT J. , SINGER A. , BANIN A.
Published: July 2006

Cd adsorption isotherms were measured on five Israeli soils ranging in specific surface area from 65 to 315m2/g. Retention capacity of Cd ranged from 4.7 × 103 to 10 × 103μg/g soil (8.4 to 17.9 mequiv/100 g soil) and was correlated with the specific surface area. Almost all the adsorbed Cd was exchangeable with 0.5 M CaCl2 and the remaining fraction was extractable in 0.5 M HCl. Plots of Kd, the distribution coefficient of Cd between the solid and solution phases, vs. Γ, the surface density of adsorbed Cd, showed that all soils behave similarly, Kd sharply diminishing with Γ. It was suggested, based on comparison with literature data on Cd adsorption on montmorillonite, that below γ s 0. 5 × 1017 ions/m2, specific adsorption mechanisms prevail whereas above it the adsorption is mainly due to electrostatic interactions and ion exchange.
THE STRUCTURE OF BEDS OF SPHERICAL PARTICLES
Authors: DEXTER A. R. , HEWITT J. S.
Published: July 2006

The statistical distributions of intercepted void and particle lengths along lines through beds of random close packed equal spheres are analysed. The structures are described by sets of sixteen conditional porosities. Data are presented for 21 different sphere diameters.

The intercepted void and particle lengths are given for two sizes of spheres having diameters in the ratio 1:0.8. The results are not very different from those for equal spheres.

The effect of data length on the accuracy of the conditional porosities is measured for four representative particle diameters. A method for calculating pore size distributions from the conditional porosities is presented.
EFFECTS OF IONIC STRENGTH AND NATURE OF THE CATION ON DESORPTION OF PHOSPHATE FROM SOIL
Authors: BARROW N. J. , SHAW T. C.
Published: July 2006

The effects of cations on desorption of phosphate previously added to soil were studied by mixing phosphated soil with solutions of chloride salts at a range of solutionitoil ratios and for periods which ranged from 1 to 96 h. Phosphate desorbed was then related to the experimental variables by a pair of simultaneous equations. In calcium chloride, the rate of desorption of phosphate was inversely proportional to the calcium concentration. Desorption was faster in 0.01 M magnesium chloride than in 0:01 M calcium chloride, and faster in 0.03 M sodium chloride than in either magnesium or calcium chloride. Addition of a further supply of the cation on an exchange resin increased the rate for both sodium and magnesium but decreased it for calcium. A range of monovalent cations formed a sequence from fastest to slowest of: Li+ > Na+ > NH4−> K +, Rb + > Cs +. The identity and concentration of the cations had a large effect on the concentration of phosphate when the solution: soil ratio was small. There were also large effects in the amount of phosphate desorbed when the solution: soil ratio was large and the concentration of phosphate approached zero. This suggested that the escaping tendency of the phosphate was decreased when the cations which balanced the negative charge on the adsorbed phosphate were close to the surface.
THE DESCRIPTION OF DESORPTION OF PHOSPHATE FROM SOIL
Authors: BARROW N. J.
Published: July 2006

After incubation with soil, phosphate was desorbed in dilute calcium chloride solutions. After short periods of incubation, the amount of phosphate desorbed increased rapidly at first but then net re‐adsorption occurred. After long periods of incubation, desorption was slower and there was no net re‐adsorption with prolonged desorption.

Desorption was described in terms of two limiting values: the amount of phosphate (K) which would be desorbed as the concentration of phosphate approached zero, and the solution concentration of phosphate (Co) at which no desorption occurred. Both values decreased as the period of incubation increased. The value of K increased during the desorption phase, but the value of Co decreased. The decrease in Co during desorption was most marked after short periods of incubation and was important in describing the trend for re‐adsorption of phosphate.
POTASSIUM FIXATION IN SOME KENYAN SOILS
Authors: BARBER R. G.
Published: July 2006

Potassium fixation was measured for 13 Kenyan soils with a range of applied potassium (0 to 1000 mg kg−1). The fixed potassium was measured, and hence is defined in this study, by the difference between the amount of applied K and the increase in the extractable K after equilibration, using a single ‘equilibrium’ extraction procedure with 0. 25 M Cad, as the extractant. At application rates of 50 and 1000 mg kg−1 the fixed potassium varied from −52% to 64% and 7% to 39% respectively. A correlation was found between the K fixation and % clay content at the 1000 mg kg1 application rate. Estimates of the % fixation by the clay fractions gave 53 to 80% for montmorillonites, 48 to 66% for amorphous clays and 19 to 32% for kaolinites. It is suggested that the amorphous clays may fix potassium by a ‘sieve’ mechanism.
INFLUENCE OF THE SPATIAL DISTRIBUTION OF NITRATE ON THE UPTAKE OF N BY PLANTS: A REVIEW AND A MODEL FOR ROOTING DEPTH
Authors: BURNS I. G.
Published: July 2006

Published literature is re‐examined in an attempt to understand the influence of the spatial distribution of soil nitrate on N uptake in order to devise a simple method for estimating the depth to which nitrate must be leached before it becomes unavailable to the crop. The evidence suggests that most crops can continue normal growth with less than 15% of their roots exposed to nitrate.

A simple model of nitrate uptake is constructed in which nitrate is assumed to be totally available above a set depth and totally unavailable below it. This effective rooting depth is assumed to coincide with the depth at which uptake per unit length of root declines to half of the maximum rate. Estimates of effective rooting depth have been made from root distribution data for various vegetable crops grown at Wellesbourne and cereal crops at Rothamsted. The results were found to fit a simple regression equation which can be used to calculate effective rooting depths at any stage of growth from the dry weight and population density of the crop and the mean cross‐sectional area of its roots. This equation is used in the succeeding papers to estimate the effects of leaching on the N fertilizer needs of crops.
THE WATER BALANCE OF AN AGRICULTURAL CATCHMENT. I. ESTIMATION OF EVAPORATION FROM SOIL WATER RECORDS
Authors: McGOWAN M. , WILLIAMS J. B.
Published: July 2006

Errors of measurement of soil water content with the neutron probe can be made small enough for most water balance studies; and apart from the possible damage resulting from access tube implacement, they can be readily specified. A more important problem is estimating how much water is lost from soil by drainage.

A simple, graphical method is described to distinguish between drainage and evaporation from soil, based upon identification of the maximum depth at which measurable quantities of water are extracted by roots. As a result of errors in soil water measurements and uncertainties in the distinction between drainage and evaporation, estimates of soil water deficit and hence evaporation for a single profile are likely to have a precision of about ±5 mm. Larger variability is commonly found in soil water storage changes measured in replicate profiles partly because of uneven wetting of the soil during rain and partly because of non‐uniform losses by drainage and root extraction. This variability requires careful attention to replication and location of access tubes when assessing the evaporation for a particular site.
DESORPTION OF PHOSPHATE FROM SOILS USING ANION EXCHANGE RESINS
Authors: BACHE B. W. , IRELAND CHRISTINA
Published: July 2006

After 100h reaction with Cl‐resin and 300h reaction with HCO3‐resin (approaching equilibrium), the concentration of anions complementary to phosphate was the critical variable affecting the transfer of P from soil to resin. Solution concentrations of H30+, Ca2+ and phosphate indicated that desorption of P by OH‐, and dissolution of Ca phosphates, controlled P release from soils. P extracted by HCO3‐resin was much greater than by Cl‐resin from an acid soil, due to lower total anion and higher desorbing anion concentrations, but there was little difference between the two resins with a calcareous soil. HCO3‐resin extracted a constant proportion of isotopically‐exchangeable P from different soils whereas Cl‐resin did not. Anion exchange resins provide a convenient means for producing P desorption curves for soils.
THE INTERACTION OF PHOSPHATE WITH AN ANION EXCHANGE RESIN
Authors: CHRISTENSEN HANS HENRIK , POSNER ALAN M.
Published: July 2006

Phosphate adsorbed on an anion exchange resin was titrated with sodium hydroxide. The inflection point which corresponds to the second pK value of phosphoric acid in solution, was lowered 0.9 pH‐unit when the acid was absorbed on the resin. This shift was fully explained by the exclusion of H+ from the resin due to a Donnan equilibrium.

The adsorption characteristic of the single and double charged phosphate ion on an anion exchange resin was examined at different pH values and phosphate:resin ratios. A model was suggested for the observed adsorption pattern.
IMOGOLITE AND PROTO‐IMOGOLITE ALLOPHANE IN SPODIC HORIZONS: EVIDENCE FOR A MOBILE ALUMINIUM SILICATE COMPLEX IN PODZOL FORMATION
Authors: FARMER V. C. , RUSSELL J. D. , BERROW M. L.
Published: July 2006

Examination by infrared spectroscopy and electron microscopy of the fine clays (<0.5 μm) dispersed at pH 3.5 from H2O2‐treated soil indicates that imogolite and proto‐imogolite allophanes are concentrated in podzolic B2 and B3 horizons, and make up at least 6 percent of one B2 horizon soil, which contains virtually no layer silicate clays. It is argued here that imogolite‐type components are the principal source of extractable aluminium and silicon in such horizons, that they may act as cementing agents in indurated horizons, and that proto‐imogolite, a soluble aluminium‐silicate complex, is the predominant mobile form in which aluminium is transported to B2 and lower horizons of podzols. Comparison of the amounts of aluminium extracted by acetic acid with those extracted by EDTA indicates that extractable aluminium in Bhg, Bh, and organic‐rich A2 horizons is present principally in organic complexes. It is proposed that the aluminium fulvates concentrated in these horizons are formed in situ.
RAINDROP IMPACT STRESS
Authors: GHADIRI H. , PAYNE D.
Published: July 2006

Estimates of rain drop impact stress were made from measurements of the penetration of water drops through nylon meshes, from analysis of cine photographs of splash and from the output of a force transducer.

Results indicated maximum stresses of 2–6 MPa acting for about 50 microseconds on the perimeter of a circle corresponding with the shape of the initial rebound corona.
Critical potassium potentials for crops. I. The effect of soil type on the growth of ryegrass and creeping red fescue
Authors: PAGE M. B. , TALIBUDEEN O.
Published: July 2006

The quantity: potential relationships for Ca→K exchange in six soils were evaluated, where potential is defined by ΔGK,Ca+Mg. Using the percentage K saturation of the CEC as the index of quantity, the Worcester Series soil, rich in hydrous micas, was shown to have the highest concentration of K selective sites, and Newport Series soil, with mainly kaolinitic clay, the lowest. The other soils, containing mainly smectites, had intermediate K selectivities.

An algebraic transformation of this relationship to separate the effects of exchangeable K and CEC showed that 0.01 m CaCl2 released more K than m ammonium acetate. From the exchangeable K : ΔG relationship, two regions of K buffering were observed for all but the Newport soil, the transition occurring at a mean ΔGK,Ca+Mg value of −20.7 kJ mol−1, signifying the K concentration below which K from ‘perlpheral’ regions of micaceous minerals is released. This may explain why the percentage K saturation of the CEC of a soil cropped exhaustively (without K manuring) in the field does not drop below a minimum value.

Based on pot experiments, exhaustion and optimum K potentials (ΔGexh and ΔGopt) were derived from second‐degree polynomials fitted to the response curves of plant dry matter yield against ΔGK,Ca+Mg for five soils, the Worcester soil showing little response. ΔGexh was inversely related to the 2 : 1 layer silicate content of the soil (r2=0.98 and 0.94 for ryegrass and fescue respectively), and similarly, ΔGopt, to their CEC values (r2=0.74 and 0.77). Potassium uptake was more closely correlated with exchangeable K than with ΔGopt.
The polarographic study of the equilibrium between humic acid and aluminium in solution
Authors: RITCHIE GERALDINE S. P. , POSNER A. M. , RITCHIE I. M.
Published: July 2006

Differential pulse polarography (d.p.p.) was used to investigate the equilibria between humic acids and aluminium in solution. A reduction potential for humic acids was observed at −1.5 V but only at pH < 3.4. No reduction potential was evident for the metal humate complex. Determination of the free aluminium in solution showed that very little free aluminium (<0.1 percent of total concentration) is in equilibrium in solution with the complex before precipitation.
Chemical and mineralogical properties of sandy and loamy‐sandy ochreous brown earths in relation to incipient podzolization in a brown earth—podzol evolutive sequence
Authors: HERBAUTS J.
Published: July 2006

Chemical and mineralogical properties of ochreous brown earths have been studied with particular reference to: (1) the distribution within the profiles of Fe and Al compounds; (2) the occurrence of smectite‐like clay minerals in surface horizons.

Ochreous brown earths studied belong to a developmental sequence of forest soils, from acid brown earths to ferric podzols, developed on sandy or loamy‐sandy acid parent materials. In such a soil sequence, both selective chemical and mineralogical data show clearly that podzolization is already active in ochreous brown earths, whereas such an incipient podzolization is quite undetectable by direct morphological observations.

The distribution patterns of amorphous Fe and Al hydrous oxides and organic associations, clearly show the intergrade character of ochreous brown earths, when compared with the vertical distribution of Fe and Al forms in acid brown earths and podzolized soils. The Fe/Al ratio of both an NH4‐oxalate extract and an NaOH/Na‐tetraborate extract buffered at pH 9.7, measured in the A1B diagnostic horizon of ochreous brown earths, is a particularly appropriate and useful genetic criterion for the detection of incipient podzolization.

Moreover, the presence of expansible clay minerals (degradation smectites) in the clay‐sized fraction of the surface horizons of ochreous brown earths (A1 and A1B) can be considered as supplementary evidence of incipient podzolization.
Adsorbed ion activities and other thermodynamic parameters of ion exchange defined by mole or equivalent fractions
Authors: GOULDING K. W. T.
Published: July 2006

The ‘Gaines and Thomas’ method for calculating the thermodynamic parameters of a cation exchange process has been criticized because equivalent rather than mole fractions were used in the definition of adsorbed ion activity coefficients. Although such coefficients are thus not theoretically correct, comparison with directly measured enthalpies of exchange shows that they indicate heterogeneity in the exchange process correctly. They also differ little from coefficients defined in terms of mole fractions. Such a re‐definition alters values of the thermodynamic equilibrium constant, and free energy and entropy of exchange by a constant factor, independent of cations and exchanger. Comparisons of series of cations, soils or clays using these parameters are therefore not affected.
Chemical properties of upland peats influencing the retention of phosphate and potassium ions
Authors: CUTTLE S. P.
Published: July 2006

Peat samples representing depths of 0–15 cm and 15–30 cm were obtained from 11 upland sites in southern Scotland. Their pH, ash content, cation exchange capacity, phosphate sorption index and contents of 0.1 m hydrochloric acid‐extractable iron and aluminium were determined as indicators of the extent to which phosphate and potassium ions would be retained following afforestation and application of fertilizers to these sites.

In all soils cation exchange capacities were considerably larger than the quantity of potassium normally applied as fertilizer. Phosphate sorption indices were closely related to the content of extractable iron and aluminium in the peat samples. When expressed on a volume basis, the indices were low compared with those published for mineral soils, and some peats appeared to have almost no capacity to sorb phosphate ions from solution.
1H‐nuclear magnetic resonance study of a soil humic acid
Authors: WILSON M. A. , COLLIN P. J. , TATE K. R.
Published: July 2006

The structure of a humic acid from a New Zealand pasture topsoil has been investigated by 1H‐n.m.r. spectroscopy. The work complements a recent 13C‐n.m.r. study on the same humic acid. Irradiating the water peak in the spectrum greatly improves spectral quality. The results show that the proton aromaticity of the humic acid (excluding exchangeable protons) is 17%. Considerable amounts of protons in the humic acid are associated with carbohydrates (35%). Useful structural parameters describing the average molecular structure of the humic acid were derived by combining both 1H and 13C data. Further work is needed to determine both the percentage exchange of protons in alkali and the percentage of inorganic hydrogen in humic acids, before the condensation and the degree of substitution of aromatic rings can be quantitatively estimated.
The calibration of a high resolution gamma‐ray transmission system for measuring soil bulk density and an assessment of its field performance
Authors: HENSHALL J. K. , CAMPBELL D. J.
Published: July 2006

The calibration of a high resolution gamma‐ray density probe and a simple experiment comparing the probe with an earlier, lower resolution version are described. An assessment is made of the performance of the probe in three experiments investigating compaction by tractor wheels, two of which were in the field and the third in an indoor soil tank. A linear calibration relationship was obtained, although the addition of a quadratic term improved the fit of the curve slightly. The probe was found to be much more accurate than the earlier version within 100 mm of the soil surface where treatment effects were largest and most numerous in the field experiments, and thin layers of high density could be detected. Over the 15 month period of the experiments, the stability of the system was found to be satisfactory.
A comparison of the structural characteristics of polymaleic acid and a soil fulvic acid
Authors: SPITELLER M. , SCHNITZER M.
Published: July 2006

The purpose of this investigation was to compare structural characteristics of PMA with those of FA in order to assess the suitability of PMA to serve as a model for FA. Chemical (elemental analyses, CO2H group determinations, increases in OCH3 after methylation, oxidative degradation) and spectroscopic (visible, UV, fluorescence, IR, 13CNMR, and ESR) methods were used for this purpose. While PMA was found to resemble FA in a number of characteristics (water solubility, rich in CO2H groups, dark brown colour), it significantly differed from FA in a number of respects (UV, fluorescence, 13CNMR spectra as well in oxidation products). Compared to FA, PMA appeared to be better organized and more homogeneous at the molecular level, richer in olefinic structures and less aromatic. But the chemical structures of both PMA and FA remain largely unknown.
The extraction and characterization of soil polysaccharide by whole soil methylation
Authors: CHESHIRE M. V. , MUNDIE C. M. , BRACEWELL J. M. , ROBERTSON G. W. , RUSSELL J. D. , FRASER A. R.
Published: July 2006

A soil of the Countesswells series was repeatedly methylated by the Hakomori procedure and a chloroform‐soluble product isolated after each methylation. Ninety‐two per cent of the material engendered by seven methylations was released during the first four methylations. This had a methoxyl content of about 20% and contained 2% N. Later fractions had lower methoxyl and N contents.

Residual carbohydrate in the soil had reducing sugar content on hydrolysis, equivalent to about 3% of the original value.

The extracted material had the infrared spectrum of a methylated soil polysaccharide and, on hydrolysis by 2 m trifluoracetic acid, released methylated sugar derivatives of which 68 were characterised by GC‐MS.

Derivatives corresponding to (1→4) linked sugars predominated for both hexose and pentose sugars but there was also a large proportion of (1→3) linkages, (1→3) linkages predominated for the deoxyhexose sugars. There were more sugars with only one or two methylated hydroxyl groups than could be accounted for as branching points because of the relatively small numbers of end groups.

Prior reduction of the soil with sodium borohydride had no measurable effect on the nature or yield of the methylated product. This indicates that amino acid sugar linkages susceptible to β‐elimination reactions can have only a very small influence on the reaction.

The isolated sugar derivatives accounted for 70% of the total soil sugars. The methylated material before hydrolysis had a low nominal molecular weight on diafiltration, with 68% < 10000. Some of the sugars unaccounted for were probably lost during the dialysis stage necessary to remove dimethyl sulphoxide.
Removal of ferrous iron from field drainage waters by conifer bark
Authors: VAUGHAN D. , WHEATLEY R. E. , ORD B. G.
Published: July 2006

Iron ochre deposition in field drainage systems is produced as a result of chemical and microbiological oxidation of ferrous iron in soil solution to the insoluble ferric form. Conifer bark, from several plant species, will absorb ferrous iron from solution quickly and irreversibly, the bark changing colour from brown to blue in the process. This bark, unlike that from deciduous trees, contains only small quantities of soluble phenolic components so it does not create an environmental problem under field conditions. Trials carried out at a test farm, where bark was placed within nylon mesh sacks and incorporated into the drainage system, were very successful, and drainage pipes which had previously blocked twice yearly remained relatively free of ochre. The use of bark from conifers can offer an inexpensive method of ameliorating the problem of ochre formation without producing environmental pollution.
The morphology and genesis of eight surface‐water gley soils developed in till in England and Wales
Authors: MURPHY C. P.
Published: July 2006

The morphology is described of eight surface‐water gley soils developed in til in Wales and central and northern England. Physical and chemical analyses as well as micromorphological observations are used to investigate processes affecting the genesis of the soils.

The characteristic property of surface‐water gley soils, namely slowly permeable subsurface horizons, causes a degree of periodie waterlogging within the profile. Effects of gleying and shrink/swell processes are described.

Three main aspects of weathering are shown to be operating: decalcification in two of the three calcareous profiles, the breakdown of coarse into finer particles and the alteration of the clay fraction, chiefly the formation of mixed‐layer minerals from mica.

Argillic B horizons are present in some soils. In profiles developed in calcareous till the degree of decalcification relates strongly to the amounts of recognizable clay concentrations as seen in thin section. Of the other five profiles three clearly have argillic B horizons. Problems associated with the identification of argillic B horizons in surface‐water gley soils in till are discussed.
Drilling vegetables into autumn‐cultivated soil with a low ground pressure vehicle: effects on timeliness and soil compaction
Authors: ROWSE H. R. , GOODMAN D.
Published: July 2006

Secondary cultivations for the spring‐sowing of vegetables are often delayed because they cannot be carried out until the soil to the depth of cultivation has dried to the plastic limit (i.e. it crumbles rather than smears). It is suggested that doing secondary cultivations in the autumn, and then drilling in the spring without further cultivation, would be less liable to delays because only the soil down to the depth of drilling need dry below the plastic limit. Simple models are derived to calculate soil water contents from weather data. They show that between 1960 and 1981 the 0–120 mm layer (representing a typical cultivation depth) dried beyond the plastic limit for an average of 36% of the days between 14 February and 9 May, compared with 68% for the 0–30 mm layer (proposed system). Wheel sinkage, bulk density and cone resistance measurements showed that a tractor would cause excessive compaction when only the surface 30 mm was drier than the plastic limit, but this could be minimized by using a low ground pressure vehicle.
An assessment of an approximate analytic method for predicting breakthrough curves for steady state longitudinal dispersion of solute in soil with non‐uniform water distribution
Authors: TOWNER G. D.
Published: July 2006

Breakthrough curves have been determined using an analytic solution of the dispersion equation for constant water content—set equal to the mean water content—and compared with those obtained for the actual water distribution using an analysis developed by Wilson & Gelhar (1981). Numerical analysis of selected examples confirmed the validity and accuracy of the latter method.

The error in using the mean water content could become unacceptably large when the water content range was large or changed abruptly with distance, but was other‐wise small and probably negligible for many applications. It was not possible to devise simple criteria, but the method of Wilson & Gelhar is simple to apply, and it is unnecessary to consider alternative approximate methods.
Thermodynamics of K‐Ca exchange in soils
Authors: GOULDING K. W. T. , TALIBUDEEN O.
Published: July 2006

The standard and differential thermodynamic properties of K‐Ca exchange in soils from the Broadbalk (Batcombe series) and Saxmundham Rotation I (Beccles series) Experiments were evaluated for selected manurial treatments, using exchange isotherms and calorimetric measurements. The Beccles soil had a greater preference for K than the Batcombe soil in all the comparable treatments (Nil, PK and FYM). In all the soils, enthalpic forces favoured K preference but entropic forces Ca preference; in all but two cases the magnitude of the enthalpic forces were greater, resulting in K preference (positive ‐ΔGo). The ‐ΔHo values of the soils did not vary greatly, and the main cause of variation in ‐ΔGo values was that in ‐TΔSo values. Residual fertilizer K and FYM residues decreased preference for K at both locations, but more so at Broadbalk than at Saxmundham, presumably because of the greater duration and amount of K manuring at Broadbalk. FYM residues had a very complex effect on the exchange characteristics of Broadbalk soil. It is suggested that these differences are caused by the different pH values of the surface soils before they came into arable usage, which reflect their contrasting parent materials and pedogenic histories, and by the different durations and extents of manuring in the two experiments.
On estimating the uptake of nutrients solubilized near roots or other surfaces
Authors: NYE P. H.
Published: July 2006

The additional nutrient absorbed by a surface releasing a solubilizing agent is predicted. The ‘solubilizing effect’ is defined. The nutrient solubilized may diffuse away from the surface as well as towards it. If the change in solution concentration of nutrient and solubilizing agent at the surface are abrupt, the fraction of nutrient solubilized that is absorbed at a planar surface equals 1/(1 +√DY/DX), where DY, DX are the diffusion coefficients of the solubilizing agent and the nutrient. At a spherical surface this fraction has to be multiplied by 1/(1 +√πDY/t2a), and at a cylindrical surface, appropriate for a root, by approximately 1/(1 +√πDY/t4a), where a is the radius.
Denitrification losses from 15N‐labelled calcium nitrate fertilizer in a clay soil in the field
Authors: COLBOURN P. , HARPER I. W. , IQBAL M. M.
Published: July 2006

Calcium nitrate fertilizer containing 92.3 atoms % excess nitrogen‐15 was applied on 5 May 1981 at a rate equivalent to 100 kg N ha−1 to a clay soil in southern England cropped to winter wheat. Samples of the soil gases were collected frequently during the following 3 weeks. The soil oxygen concentration declined to 5% after 60 mm rain. A maximum of 1.5 ± 0.5 atom % N‐15 enrichment in labelled N2 gas (29N2) was detected in the soil atmosphere on 28 May. Total denitrification losses, calculated from air‐filled pore space and rates of gas loss from the soil estimated using a Fick's law approximation, were 9.5 kg N ha−1 with a daily rate of 0.30 ± 0.07 kg N ha−1. Estimated total losses were greater than 30 kg N ha−1, 93% in the form N2, but the estimation depends on several assumptions about the amount of double labelled gas (30N2), rates of gas diffusion and flux.
Characteristics of soil organic matter in temperate soils by Curie point pyrolysis‐mass spectrometry.
Authors: BRACEWELL J. M. , ROBERTSON G. W.
Published: July 2006

This series of papers examines some significant differences in the constitution of organic matter found amongst major soil groups and their genetic and morphological horizons, as determined by the dynamic pyrolysis‐mass spectrometry of whole soil samples. Multivariate methods of data analysis identify groups of co‐variant mass ions which successfully partition samples in terms of the above soil categories, and correlate with other major properties such as humification and hydromorphism.

This first study covers the A horizons from a group of 22 Scottish soils chosen from the major temperate soil groups including brown forest soils, podzols, and noncalcareous, peaty and humic gleys (phaeozems, cambisols, podzols and gleysols). The principal components analysis of 52 mass ion intensities was found to partition the soils successfully in terms of two main factors which represented 62% of the total statistical variance.

The first factor was found to correspond closely to the extent of hydromorphism, being high for highly gleyed A horizons, and depended chiefly on the presence of aromatic hydrocarbon ions. The second factor corresponded to the extent of mull humus formation, being high for brown forest soils (phaeozems, cambisols) and low for podzols, and depended chiefly on the abundance of polypeptide products relative to polysaccharide products. This second factor was evidently a more comprehensive expression of a humification factor found in previous studies.

The relationships of these factors with C and N content and with base status properties were examined.
Interpretation of leaching under multiple fertilizer applications
Authors: BARRY D. A. , ROSE C. W. , SAFFIGNA P. G. , PARLANGE J.‐Y.
Published: July 2006

Simple theory has been developed and illustrated elsewhere which allows estimation, firstly, of the mean depth of solute penetration from any sequence of infiltration and evapotranspiration events, and secondly, of the apparent dispersion about this mean depth used as a Lagrangian coordinate system. This theory was used to analyse and interpret the time patterns of leachate concentrations of NO3‐N and Cl of a field lysimeter with a potato crop receiving four fertilizer applications and numerous inadvertent N and Cl applications by irrigation with groundwater. The assumption of superposition of estimated solute concentrations was employed in the analysis, yielding results consistent with the data. The analysis has quantified the leaching loss from each fertilizer application.