Showing papers in "European Journal of Soil Science in 1964"

Loss-on-ignition as an estimate of organic matter and organic carbon in non-calcareous soils

Abstract: Summary Examination of data on North Wales soils shows that a good correlation exists between loss-on-ignition and organic C values, determined by Tinsley's method. Ignition for half an hour at 850° C, and for 16 hours at 375 ±5° C have both been employed. The latter has advantages over the former procedure. Regression lines and prediction limits for organic C from loss-on-ignition are given from the data obtained. Although these regressions are not necessarily expected to be generally applicable, examination of some published data suggests that closely similar expressions may be. The method, because of its simplicity, can be usefully applied in a wide range of survey, analytical and ecological studies, in spite of the known sources of error.

Studies on soil potassium ii. the ‘immediate’ q/i relations of labile potassium in the soil

Abstract: Summary The Q/I relations of labile soil K relate its availability or intensity (I) to the amount (Q) present. The activity ratio aK/√(aCa±Mg) has already been proposed as a measure of the intensity factor (part I). The ability of a soil to maintain the activity ratio against depletion by plant roots is governed partly by the character of the pool of labile K and also by the rate of release of fixed K, and by the diffusion and transport of K ions in the soil solution. We may isolate the Potential Buffering Capacity of the pool of labile K by determining the Q/I relation over short periods. Such immediate Q/I relations have been determined for a number of soils. They are all linear over the range of activity ratios commonly encountered in agricultural soils and approximate to familiar ion-exchange equations. At low values of the activity ratio the Q/I relations are all curved and asymptotic to the Q-axis. The effects of drying, pH, the addition of lime or K fertilizers, and changes in temperature on the form of the Q/I relations are reported. Oven-drying a soil, particularly if repeated, appears to cause proportionately more K than Ca to be fixed in the fine clay fraction.

Studies on soil potassium

Abstract: The Quantity-Intensity relations of labile K in soil relate the intensity (or availability) of labile K to the amount of labile K present. Several soils have been depleted of K by crops, and enriched or depleted of K by other means. Theforms of the Q/I relations for labile K in these soils are almost unaffected by K-depletion, by the fixation of added K on storage, or by the release or fixation of K by heating. The addition of very large amounts of K may cause transient changes, but these changes disappear on storing the soil.

Toxicity as a cause of the inefficiency of urea as a fertilizer.

Abstract: Summary Plant damage and reduced yields were associated with delayed ammonification or nitrification of added urea-nitrogen In a neutral sandy loam, the adverse effects of urea application were associated with the accumulation of toxic levels of first ammonia and later nitrite Addition of hydrogen-ion as phosphoric or sulphuric acid alleviated the damage thereby supporting the conclusion that ammonia and nitrite accumulation were the causes of phytotoxicity In an acid sand, toxicity was associated first with the presence of large quantities of urea remaining in the soil though the evidence was insufficient to show in what way the urea was toxic There was then a second phase of toxicity associated with the presence of considerable quantities of ammonium-nitrogen under conditions where toxic levels of ammonia were likely to have occurred The later phase (nitrite toxicity) did not occur Phytotoxicity arising from urea addition to the soil could be due apparently to the persistence of urea as such in the soil and also to the accumulation of significant quantities of free ammonia and nitrite The occurrence of one or more of these phases of urea toxicity depended on differences in soil conditions

Aluminium and iron phosphate studies relating to soils

Abstract: Summary The determination of ion activities in solution during the sorption of phosphate on to gibbsite and hydrous ferric oxide has shown three stages to the reaction: (i) a high energy chemisorption of small amounts of phosphate; (ii) precipitation of a separate phosphate phase; (iii) a low energy sorption of phosphate on to the precipitate. The values of ion activity products for the precipitation reaction do not correspond with the solubility constants of variscite and strengite. Ion activity products are not likely to be useful for indicating the existence of separate A1 and Fe phosphate phases in soils. The variation of solution phosphate activity with phosphate sorbed is suggested as a basis for a ‘phosphate characteristic’ curve for phosphate-reactive heterogeneous systems.

Toxicity as a cause of the inefficiency of urea as a fertilizer. i. review

Abstract: Summary The causes and mechanisms of phytotoxicity that can bring about poor or adverse crop responses to applications of solid urea to soil are reviewed Compounds which may cause phytotoxicity are urea, transformation products of urea formed during manufacture (biuret), and transformation products produced in the soil or in plants (cyanate, carbamate, ammonia, and nitrite) Of these, ammonia and nitrite are considered to be the most likely causes of phytotoxicity when urea of low biuret content is used

Some factors affecting losses of ammonia from urea and ammonium sulphate applied to soils

Abstract: Summary Urea supplying 100 1b of N/acre was either broadcast on the surface or mixed with four soils (two clay-loams, two sandy-loams) and losses of ammonia were measured when the soils were maintained at 40, 50, or 60 per cent water-holding capacity (WHC) and incubated at 5°or 25°C. Urea and ammonium sulphate were similarly applied to two calcareous soils at 40 per cent WHC and 5°or 25°C. Losses varied most among soils, from 2 per cent of the N applied from an unmanured clay-loam to 13 per cent from an unmanured sandy-loam. Changing temperature and water content affected losses little on average, but their effects differed with different soils. Losses of ammonia were similar from urea and from ammonium sulphate applied to the calcareous soils. Analyses at the end of the experiments showed that: (i) nitrite tended to accumulate in the sandy and calcareous soils, accumulation being favoured by lower temperature and wetter soil; (ii) ammonia was lost at 25° C from calcareous soils until all the ammonium- N had been nitrified, from the slightly alkaline clay soils until nine-tenths had been nitrified, and from the neutral sandy soils until half had been nitrified.

A soil catena on granite in southern rhodesia

Abstract: Summary A catena on the Mid-Tertiary surface near Salisbury, Southern Rhodesia, has developed over granite. Both land form and rock form indicate a two-cycle landscape. The climate is sub-tropical with a 33-in. rainfall and the vegetation is a variant of Braclzystegia savannah woodland. Profiles of good and imperfect drainage have three main horizons, namely, M (mineral); over, F/S (ferricrete and stones); over, W (weathered rock) horizons. Poorly drained soils exhibit G (gley) horizons. The W horizon of a hill-top soil comprises material at an early weathering stage below 12 ft having a platy structure, well-developed clayskins, and fresh minerals, but older material above that depth does not correspond to Van Wambeke's criteria for ante-Pleistocene materials. Dynamic soil-forming processes include lateral movement of the M horizon by sheetwash and truncation of the W horizon by insect activity.

Cation exchange reactions

Abstract: Summary Wyoming bentonite, Blisworth illite, and a fen peat were saturated with different proportions of calcium, magnesium, and potassium, and exchange between these cations was studied by measuring their activity ratios in dilute equilibrium solutions. With both clays the activity ratio aMg/aCa in solution was linearly related to the ratio of adsorbed Mg/Ca, the former being 1.22 times larger than the latter ratio. Peat held magnesium much less strongly than calcium, and the difference increased with increasing magnesium saturation. With all three materials the activity ratio aMg/aCa+Mg in solution was curvilinearly related to the percentage magnesium saturation. Peat adsorbed potassium less strongly relative to the divalent cations than did the clays, and bentonite adsorbed potassium less strongly than illite. Decreasing the Ca:Mg ratio increased the strength with which peat adsorbed potassium, but had no effect on potassium adsorption by the clays. Exchange between magnesium and calcium in forty British soils was studied by measuring the concentration ratio [Mg]/[Ca+Mg] in equilibrium soil solutions. The relation between [Mg]/[Ca+Mg] in solution and the ratio of exchangeable Mg/(Ca+Mg) in different soils varied within the range covered by peat and bentonite or illite, suggesting that differences between soils might be due to different organic-matter contents. The extent to which [Mg]/[Ca + Mg] in solution was altered by changes in the exchangeable magnesium content differed considerably between soils. These differences were not all explained by variations in exchange capacity, showing that different soils adsorb magnesium with differing strengths relative to calcium.

Polyphenols in plant, humus, and soil iii. stabilization of gelatin by polyphenol tanning

Abstract: Summary The role of polyphenols in the stabilization of protein in superficial humus and the relationship of this role to mull and mor formation is discussed. Polyphenols extracted from a variety of plant materials were used to tan gelatin over a wide range of pH. The stability of gelatin, tanned with polyphenols extracted from green beech leaves (mor site), against microbial degradation was then estimated. Over the range of pH found in soils, stability was greatest when the pH of the tanning was low. It seems likely that mor-forming plant species contain more efficient tannins and the acid condition of the associated soil is better suited to the tanning process. Quantitative differences in tanning substances between mull and mor sites have already been reported by us (Coulson et al., 1960a).

Influence of organic materials on the determination of the spectfic surface areas of soils

Abstract: Summary The surface areas of a number of soils have been determined before and after removal of organic matter by treatment with hydrogen peroxide. The external area as determined by low-temperature nitrogen adsorption increased after peroxidation. The total area derived from the nitrogen area and cetyl pyridinium bromide (CPB) adsorption generally decreased. Part of the clay-organic complex was separated from some soils, and the external and total surface areas of this material before and after peroxidation determined similarly. Both the external and total areas increased after peroxidation. These results indicate that soils contain organic materials which are not part of the clay-organic complex and which adsorb large amounts of CPB on surfaces not accessible to nitrogen molecules. A sample of peat showed a correspondingly high CPB adsorption and low nitrogen area. The large differences that occur in the nitrogen and CPB areas after peroxidation show the importance of removal of organic matter prior to the determination of the surface areas of soil clays. The surface areas were only slightly greater when carbon was completely removed by 30 per cent peroxide than when it was partly removed by 6 per cent peroxide. Organic compounds associated with the clay in the clay-organic complex are apparently able to prevent access of nitrogen molecules to many of the clay surfaces, and also probably exclude CPB from some of these surfaces.

Determination of the total specific surfaceareas of soils by adsorption of cetyl pyridinium bromide

Abstract: Summary Surface areas of soil clays can be determined by adsorption of cetyl pyridinium bromide (CPB) from solution. The method is best used with peroxidized, air-dry samples which have been treated with dithionite-citrate-bicarbonate to remove iron and some aluminium oxides, and made homo-ionic with respect to the exchangeable cation. Apparent CPB areas derived from the plateau of the CPB adsorption isotherm agree with nitrogen areas when no expanding lattice material is present in the sample and when no large proportion of oxides of low surface density of charge remain after the dithionite treatment. When expanding lattice material is present CPB can provide an accurate measure of the internal surfaces provided that the external area is determined independently. Real variations in the crystal size, and hence ratio of external to internal area, are found with montmorillonite, and are exceptionally large for Wyoming bentonite. Specific surface areas determined by the ethylene glycol adsorption method agree reasonably well with areas of non-expanding lattice clays determined by CPB and nitrogen provided that the specific surface coverage by each adsorbed ethylene glycol molecule is taken as 23A2. When expanding lattice material is present the agreement is less satisfactory, but is improved in most instances by correcting the area on the basis that molecules adsorbed on external surfaces cover 23A2 but those on internal surfaces cover 46A2. Within the range of surface densities of charge found for mica-type materials the adsorption of CPB is much less sensitive to differences than is ethylene glycol, and therefore enables surface areas to be determined more accurately. CPB is also considerably more convenient to use, since well-defined adsorption plateaux are formed after overnight shaking.

Cation-exchange equilibria with vermiculite

Abstract: Summary The exchange of Na, Mg, Ca, Sr, and Ba ions has been studied in the temperature range 25° C-70° C. Vermiculite shows a preference for divalent ions over Na ions at 25° C and the preference increases very greatly at higher temperatures. The preference is largely determined by the increase in entropy which accompanies the replacement of monovalent ions by divalent ions in the vermiculite. Preference is less marked between divalent ions. These ions are similarly hydrated in vermiculite, which differs in this respect from resins and most other clay minerals. The greater affinity of Mg ions compared with other divalent ions is explained by their closer approach to the silicate surfaces.

Studies on soil potassium

Abstract: Summary The method of determining the activity ratio (AR) described by Beckett in Part II of this series was applied to a range of moderately to intensely acid Nigerian soils. With the highly acid soils it was necessary to add aluminium ions to the solution to obtain equilibrium. A method for obtaining the true equilibrium solution composition for K, (Ca±Mg), and A1 is described, and a series of typical results given. It was necessary to add benzene to prevent biological activity during sedimentation at 33° C. Altering the total concentration of the solution did not affect the activity ratio. A minority of soils showed evidence of transfer of potassium to non-exchangeable forms during equilibrium. The slopes of the (exchangeable K)-AR curves in a single soil were dependent on the amounts of soil Ca±Mg present. In comparisons between several soils, exchange capacity also had an effect. The Gapon equation was approximately correct for these soils over limited ranges.

The mobilization of iron by aqueous extracts of plants

Abstract: Summary The organic-acid fraction maintains iron in solution from pH 4 to at least pH 9.5, with a maximum of 15 mg iron per gram of dried pine needles at pH 8; the amino-acid fraction is inactive above pH 4.5. The constituents of the organic-acid fraction are examined individually and their effectiveness com-pared. Of the active acids, all except phosphoric acid are α-hydroxy carboxylic acids. A synthetic solution, with a composition that corresponds to the analysis of the organic-acid fraction, is used to demonstrate that all the major active constituents have been identified. The activity of the individual acids and the organic-acid fraction is due to their ability to form water-soluble complexes with iron and to stabilize ferric hydroxide sols. The water-soluble complexes are formed over a wide range of pH and in the presence of calcium ions. The formation of ferric hydroxide sols, however, is greatly influenced by pH and by the presence of calcium ions. These findings are related to soil processes and to the morphological character of the soils on which Scots Pine trees normally grow.

A classification of humus forms and micro‐fabrics of temperate grasslands

Abstract: Summary The humus form is recognized in a soil profile as the group of A horizons in which organic matter is concentrated, and it is thus the upper part only of the genetic humus type, the true measure of which is the complete organic profile extending into B and C horizons. Grassland humus forms are subdivided on a basis of field morphology into two groups: mull, in which the organic residues are largely incorporated as an intimate clay-humus mixture, and mor, in which organic residues in varying stages of decomposition overlie the mineral soil with a sharp boundary but may show weak mechanical admixture of mineral grains. A mor-like mull intergrade is recognized where the mull is very high in intimately incorporated organic matter. According to variation in horizon thickness, structure, and consistence, sixteen humus forms are recognized: strongly granular, weakly granular, massive or blocky, fine, matted, laminated, and lenticular mulls, strongly granular, weakly granular, and laminated mor-like mulls, and granular, massive, matted, laminated, banded, and mullized mors. Where mineral grains are very abundant in mor a sandy phase is recognized. Each layer or horizon of a humus form may have one or more distinct micro-structures or fabrics. Twelve fabrics have so far been recognized under grassland: weak mull humus, strong mull humus, mull-like moder, mull-like rendzina moder, leached mull-like rendzina moder, silica moder, swollen moder, rendzina moder, leached rendzina moder, raw soil humus, sclerotial humus, and raw humus.

Studies of fungi in a podzol

Abstract: Summary The soil-sectioning technique was used to allow microscopic examination of fungal populations in relatively undisturbed samples of soil from the horizons of an iron-humus podzol at Delamere, Cheshire. The technique was also applied to a seasonal study of the quantitative changes in the fungal populations in the A0h layer of the organic horizon and the five mineral horizons of the podzol. For these quantitative assessments, measurement of length of mycelium per unit amount of soil was the most sensitive method, being superior to measurement of density of mycelium or measurement of percentage frequency of occurrence of mycelium. Considerable evidence was obtained during the seasonal study of an increase in mycelium production during the autumn–winter period of the year, clearly demonstrated in the A0h and A1 horizons. This increase in mycelium production appeared to be correlated with the period of maximum leaf fall (and with the corresponding down-wash of nutrients into the mineral soil). An attempt was made to classify (on morphological grounds) types of mycelium observed, and to relate the morphological groups to the dominant organisms previously isolated from this soil. The data obtained from this study point to the value of microscopic examination of soil in providing essential supplementary data to those obtained from cultural studies.

Soils of the ultra-basic rocks of the island of rhum

Abstract: Summary Ultra-basic and basic igneous rocks outcrop as a complex over about 20 square miles of the island of Rhum, off the west coast of Scotland. Here in a cool wet oceanic climate, where the annual rainfall varies from 55 to 130 inches, there has developed a sequence of soils from rankers to peat podzols or braunerden. The development is not a simple time relationship at a particular site because of the existence of a complex erosion, transport, and deposition cycle. There is evidence for a previous long stable period succeeded by more intense erosion, possibly ascribable to past land-use. The podzols differ from typical podzols in having no AB horizon, high pH values, and high contents of exchangeable cations, especially magnesium.

A physico‐chemical study of the propertiesof humic acids and their changes during humification

Abstract: Summary Humic acids extracted from decomposing plant and peat core samples and changes in them during the process of humification were investigated in terms of their elementary composition, the acidity and the equivalent weight, the infra-red, visible and ultra-violet spectra and the shape and size of the molecules and their weight. With progressive humification in peat and decomposing plant samples, increases were noted for the carbon content and the aromatic character of the humic-acid molecules and in the number of their alcohol and ether groups, aliphatic side chains and double bonds, while decreases were observed for the hydrogen content, the molecular weight, the equivalent weight, and the hydrophilic character of the humic acids and possibly to a minor extent also for the ionization constant and the alkoxyl and alkimide groups. It was noticed that the presence of charcoal and, to a minor extent also, of clays in decomposing plant material promoted the formation of humic acids which were very similar to those found in older peat deposits, while the presence of ash did not seem to have much effect. Humic acids derived from different peat materials were found to be very similar in structure and composition, but when different types of plant material were mixed, the humic acids formed during the first stages of decomposition were very similar to those from more decomposed samples containing only the separate components.

The potassium status of west indian volcanic soils

Abstract: Summary The potassium status of a group of unfertilized volcanic soils was measured by the intensity, exchangeable, nitric acid-soluble, fixation, and total potassium values. The soils were classified by the amount of weathering and predominant clay minerals as determined by field characteristics. The soils contained principally pyroxenes, soda-lime feldspars, and variable quantities of glass and amphiboles. There was a marked absence of potassium-bearing minerals in the fine-sand fraction. Clay content varied from 5 to 72 per cent and total potassium averaged 0.38 per cent. Neither potassium highly soluble in nitric acid nor that of limited solubility were related to percentage clay, but both were highly correlated with total potassium. Fixation of potassium was usually low. Potassium intensity, expressed by pK-1/2 p(Ca 4- Mg) values, was determined by equilibrating soil with potassium in calcium chloride solutions. Such values were shown to be similar to those from soil-solution extracts displaced by alcohol. The potassium-intensity status was highest in allophane soils and lowest in montmorillonite soils; and was correlated with exchangeable, fixed and highly soluble nitric acid potassium. The last was highly correlated with exchangeable potassium. Partial correlation coefficients showed that the major factors controlling potassium intensity were exchangeable potassium relative to exchangeable calcium and magnesium and the potassium-fixing ability.

The release of hydrogen sulphide from mud

Abstract: Summary Damage due to Has occurring in some acidic, heavy paddy soils and peaty fishponds is usually preceded by falls in temperature and atmospheric pressure. The O2, content of the water layer increases with the fall in the temperature and, as the redox-level sinks in the mud, the superficial layer of the mud is oxidized and H2SO4 is formed which releases H2S from the sulphide in its environment. The decrease of atmospheric pressure lifts the gases including H2S from the hollows of the mud into the water layer and thence into the atmosphere. The gases carry colloidal particles and render the water turbid. The released H2S may result in root-rot and deficiency diseases in the rice plants, and algae bloom and fish death in the ponds.

Cutans (clay films) and potassium availability to plants1

Abstract: Summary The influences of iron-kaolinite cutans enveloping soil aggregates on the availability of K within these aggregates were studied. Synthetic iron-kaolinite clay coatings on illite aggregates were prepared. Macroscopic and microscopic observations of the synthetically prepared aggregates indicated the formation of almost continuous, partially orientated crystalline iron-kaolinite cutans around the perimeter. There were indications that the presence of the coating tended to stabilize the aggregates. Photomicrographs of wheat root-aggregate associations revealed intimate surface contact between the two with some penetration and disruption by the wheat roots, both in the coated and uncoated aggregates. Plant growth and potassium uptake were restricted in the presence of iron-kaolinite coatings on K-rich illite aggregates compared with plants grown on aggregates without coatings. Moreover, the presence of the coatings resulted in appreciable increases in Ca and Mg accumulation by the plants. Results of this investigation suggest that cutans may modify significantly ion availability and accumulation by plants growing in highly weathered, iron-rich soils.

MECHANISMS OF FORMATION OF Na2CO3 IN SOILS

Abstract: Summary Biological transformations have been responsible for formation of Na2CO3 and resultant high alkalinity in some of the salt-affected soils of the Sacramento Valley, California. Environmental factors favouring Na2CO3 formation are high ground-water level to provide an anaerobic environment, supply of Na2SO4, and organic matter. Under these conditions, anaerobic micro-organisms reduce sulphate to sulphide and oxidize organic matter to CO2. The sulphides hydrolyse to produce free OH which combines with CO2 to form HCO3. Reduced Fe in the system inactivates the sulphides and allows accumulation of NaHCO2. Loss of CO2 from NaHCO2 during dry periods of the year results in formation of Na2CO3. In the laboratory an anaerobic environment and a supply of readily decomposable organic matter have been shown to be essential for development of HCO3 and CO3. Ultimate development of high alkalinity depends upon inactivation of soluble and exchangeable divalent bases as precipitated carbonates. Inactivation of divalent bases favours a high exchangeable Na content as well as build up of soluble NaHCO3 and Na2CO3. There is an equivalent relationship between the amount of SO4 reduced and HCO3 formed by the processes involved. The anaerobic organisms involved in the transformations obtain oxygen from the SO4 and in turn oxidize carbon of the organic matter to CO2. Development of HCO3 and CO3 is favoured in situations where organic matter and Na2SO4 concentrations are both high, but is limited in systems with a relatively low organic matter content and a high concentration of Na2SO44, or conversely, when a high content of organic matter is combined with a low salt concentration.

A preliminary study of some slope soils in wales and the welsh borderland

Abstract: Summary Data are given concerning four profiles developed in materials of loam or clay-loam texture, representative of soils found on moderate or steep slopes in Wales and the Welsh Borderland. Two acid well-drained soils with A(B)C profiles are correlated with sols bruns acides, differences in soluble Fe2O3 content probably being the result of more intense weathering in districts of greater rainfall. A humus-iron podzol described differs from typical profiles of this class in being finer in texture, and there is a significant divergence in micromorphology. The remaining soil is regarded as transitional because it has some properties of both classes. It has a prominent brown B horizon of redder hue than the overlying unbleached A horizon; organic carbon values are distinctly greater than for solsbruns acides, but there is no horizon of accumulation; SiO2/R2O3 ratios follow the pattern of variation typical of podzols though differences are less marked; the micromorphological characters of the B horizon are very similar to those of the Bs horizon of the humus-iron podzol.

The extractable manganese of soil

Abstract: Summary Exchangeable manganese extracted from soil with calcium nitrate solutions shows some increase as the period of extraction is prolonged For a given time of extraction the exhangeable manganese of soil behaves as a typical divalent cation obeying simple exchange theory, contrary to a previous report in the literature Soil particles discriminate between calcium and manganese ions, calcium ions being held more firmly

An exchange equation based on positive adsorption

Abstract: Summary An exchange equation based on positively adsorbed cations is derived using the double layer model. Some calculations using this equation are compared with calculations using the original Eriksson equation as written by Bolt.