Showing papers on "Soil organic matter published in 1976"

The effects of biocidal treatments on metabolism in soil—II. Gamma irradiation, autoclaving, air-drying and fumigation

Abstract: Respiration and mineralisation of N were measured in a set of contrasting soils that had either been autoclaved, air-dried, fumigated (with chloroform or methyl bromide) or exposed to gamma radiation. The soils used were a manured and an unmanured arable soil, an acid and a neutral woodland soil, an arable sandy soil and an organic soil under grass. With the exception of the acid woodland soil, the flushes of decomposition (i.e. the increases in O2 consumption, CO2 evolution and N mineralisation that occurred when the treated soil was inoculated and incubated for 10 days) were in the order: air-drying < CH3Br ⩽ CHCl3 < irradiation < autoclaving. All of the treatments, except air-drying, decreased the ratio (C mineralised after treatmcnt)/(N mineralised after treatment). All of the treatments increased the amount of 1N K2SO4 extractable organic C, autoclaving causing by far the greatest increase. Neither of the fumigants increased respiration in the acid soil over the whole 10 day period, although N mineralisation was slightly increased. Irradiation, air-drying and autoclaving did, however, produce a flush in the acid soil, the order being: irradiation < air-drying < autoclaving. A soluble substrate, extracted from yeast cells by ultrasonic disintegration, decomposed to about the same extent in neutral and in acid soil. When 14C labelled glucose was added to the acid soil and incubated for 52 days, the retention of labelled C was slightly greater (31·6%) than in a comparable near-neutral soil (28·8%). However, the flush that followed fumigation of the acid soil was only half that in the near-neutral soil, suggesting that less biomass is formed under acid conditions. Liming increased the size of the flush in an acid soil. For soils from the same field but under different management, the size of the flush caused by CHCl3 is in the order: grassland > cropped arable > bare fallow. The flush is much more sensitive to differences in soil management than is the total amount of soil organic matter; a fallowed soil lost half its organic C in 10 yr whereas the increase in respiration that followed fumigation fell to one-seventh its original value. Two Nigerian soils behaved similarly; a soil that had been 2 years under cultivation contained only 16% less total organic C than an adjacent soil still under secondary forest, yet the flush in the cultivated soil was half that in the forest soil. The amount of substrate metabolised during the flush is thus very sensitive to changes in soil management that alter the amount of fresh organic matter entering the soil each year.

Behavior of Chromium in Soils: II. Hexavalent Forms

Abstract: Adsorption and reduction of added Cr(VI) were characterized in soils with contrasting pH's, organic matter contents, and chemical and mineralogical properties. Presence of soil organic matter brought about spontaneous reduction of Cr(VI) to Cr(III), even at pH's above neutrality. Reduction did not occur in soils very low in organic matter unless an energy source was added. Cow manure added to practically organic-free Cecil B2 reduced Cr(IV) only after the pH had been lowered below 3 with HCl. The solubility of Cr(VI) in the presence of excess Al changed in a pattern remindful of orthophosphate. All of the soils, except a pH 7.8 Cca horizon material, adsorbed Cr(VI). Presence of orthophosphate prevented the adsorption of Cr(VI), presumably by competition for the adsorption sites. Consistent with this finding, KH₂PO₄ was found to be the best extracting agent for Cr(VI). It was concluded that behavior of Cr(VI), if it remains in soils, is similar to that of orthophosphate. However, unlike phosphate, Cr(VI) is quickly reduced by soil organic matter. Thus, Cr(VI) added to a soil will remain mobile only if its concentration exceeds both the adsorbing and the reducing capacities of the soil.

The effects of clearing and cropping on the organic reserves and biomass of tropical forest soils

Abstract: Twenty Nigerian soil samples, mainly from field experiments at the International Institute of Tropical Agriculture (IITA), were used in a study of the effects of clearing and cropping on the C, N and S reserves of soils under secondary lowland rain forest. Soils that had been cropped for 2yr usually contained less total C and N than the corresponding forest soils. This decline was less rapid when crop residues (maize) were returned to the soil as a mulch than when they were removed. The soils were incubated in the laboratory either fresh, or after exposure to stress treatments (air-drying or fumigation). The amounts of N mineralised by the fresh untreated soils were small and not clearly related to the cropping history. Both air-drying and fumigation caused a marked increase in the mineralisation of N and the amount released was related to the cropping history. Cropping caused an even greater decrease in these ‘stress-labile’ N reserves than in total soil N, so that cropping causes a decline in both the quantity and “quality’ of soil organic matter. Again, the decline was less where crops were grown under mulches. A term “Per cent Stress-labile N” (PSN), defined as the percentage of the total N mineralised when fumigated soil is incubated under defined conditions, is proposed as a measure of the ‘quality’ of soil organic nitrogen. Under secondary forest the PSN ranged from 3.4–4.2%; on cultivation it declined, in one case to less than 1%. The amount of C in the soil biomass was calculated from the size of the flush of decomposition caused by fumigation. Biomass C usually decreased on cultivation, the decrease being less under mulches. There was a close linear relationship ( r = 0.94) between the flush of N caused by fumigation and the amount of biomass C in a soil and a rough measure of biomass C can be obtained by multiplying the N flush by 8.

Products of Soil Microorganisms in Relation to Plant Growth

Abstract: A survey has been made of the range and activity of the organic products of soil microorganisms which have a direct influence on plant growth. Microbial metabolites which effect plants indirectly by the modification of the soil environment are also reviewed. The sources of substrates for the production of metabolites in soil and the farming practices which give rise to them are considered. It is stressed that an interdisciplinary approach is needed in the manipulation of microbiological activity in soil.

The accumulation of soil organic matter and its carbon isotope content in a chronosequence of soils developed on aeolian sand in new zealand

Abstract: Summary Soil organic matter was extracted by a mixture of O.IM Na4P2O: O.IM NaOH from a chronosequence of weakly weathered soils developed on aeolian sand, and fractionated into humin (non-extractable), humic acid, and fulvic acid. The mass of total organic carbon in the profiles, the 14C content and the 13C/12C ratios were also determined. The weight of total carbon increased rapidly at first and then gradually without attaining a steady state. This trend was also shown by the humin and fulvic acid fractions, but the humic acid fraction appeared to have reached a maximum after about 3000 years. The order of total weights of the organic fractions was humin > fulvic acid > humic acid. The evidence suggests that the proportions of the humic fractions formed by decomposition are related to soil differences but not to vegetation. The greater part of the plant material found in the soils appears in the humin and fulvic acid fractions.

Behavior and Fate of Metribuzin in Eight Ontario Soils

Abstract: The adsorption, desorption, and mobility of metri- buzin ( 4-amino-6-tert-butyl-3-(methylthio)-as-triazine- 5(4H)onel in eight Ontario soils were investigated. The distri- bution coefficients varied from 0.56 for the least adsorptive Fox sandy loam soil to 31.67 for the most highly adsorptive Leamington muck soil. Most of the adsorbed metribuzin was desorbed from the mineral soils after six aqueous extractions, however substantial amounts of the herbicide remained ad- sorbed on the muck soils after 10 aqueous extractions. The herbicide was relatively mobile in mineral soils but was im- mobile in the muck soils. Mobility was inversely correlated with the amount of soil organic matter. Bioassay studies indi- cated that phytotoxicity of metribuzin also decreased with increasing organic matter content of the soil. Persistence of metribuzin was dependent on microbial degradation. In a field study with Guelph loam, the half-life of metribuzin was ap- proximately 3 months.

Der Umsatz von Pflanzenwurzeln im Laufe der Vegetationsperiode und dessen Beitrag zur „Bodenatmung”︁

Abstract: The Turnover of Plant Roots during the Growth Period and its Influence on “Soll Respiration” Mustard and wheat plants were grown under 14CO2, their roots being tightly separated from the shoot sphere. Root formation, root respiration, and root decomposition could thus be followed during the plant development by radiometric methods. The total quantity of organic root matter in soil at harvest time turned out to be 20–50% larger than the amount of root residues as determined by ordinary washing procedures. Depending on the plant and duration of the experiment, an additional amount of up to three times more than this remaining root carbon was already mineralized during the vegetation period. Only one fifth of this 14CO2-production could be attributed to the respiration of living root tissue, all the remainder seemed to be due to the microbial decomposition of dead roots, root residues and root excretions. Root respiration and root decomposition together produced almost four fifths of the total evolving CO2-quantity, whilst the contribution from soil organic matter breakdown did not exceed one fourth of it. According to these data, the total rhizo-deposition amounts to 3–4 times as much organic substance than what can be found as root residues at harvest time. This rich supply of readily decomposable organic matter leads to a most intensive turnover in the rhizosphere, which should be of considerable influence on the dynamic processes in soil.

Coupled soil moisture, heat and water vapour transfers under simulated fire conditions

Abstract: An approximate numerical method is presented coupling the transfer of water, heat and water vapour in a soil. The system is used to predict in time, soil temperature profiles under simulated surface fire conditions. Moisture profiles, ground heat flux and soil evaporation are also calculated. An experiment using a tube of moist sand heated by a radiant heater over a 30 min period to simulate fire conditions was used to test the model. A further test was imposed using experimental grass fire data from the literature. In all cases deviations between observed and calculated results were small.

Estimating Potentially Mineralizable Soil Nitrogen from a Chemical Index of Soil Nitrogen AVAILABILITY1

Abstract: The feasibility of estimating potentially mineralizable soil nitrogen, N0, from direct on indirect measurements of NH4+–N produced by hydrolysis of soil organic nitrogen during 16-hr autoclaving (121°C), Ni, was investigated for 13 groups of soils comprising 475 surface and subsurface samples representing 54 soil types. The regressions of N0 on Ni for different soil groups were pooled, and the resulting equation was N0 = 4.1 (±1.0) Ni + 6.6. Apparently, therefore, the coefficient, 4.1, provides a means of reasonably estimating N0 from the chemical index, Ni, for a broad range of soils, with certain specified exceptions. Estimates of N0 from Ni together with measurements of residual mineral, plant-available N may provide a basis for developing improved N fertilizer recommendations.

The internal nitrogen cycle betweenmicroorganisms,vegetationand soil

Abstract: The major portion of the global nitrogen cycle occurs between vegetation and soil, only minor exchanges generally taking place with the atmosphere and the hydrosphere. Nitrogen conversions in soil are briefly reviewed and a global flow chart for soil nitrogen is presented. The turnover times of nitrogen in various components of this global system are compared with its turnover times in some selected ecosystems. It is shown that 95 % of the nitrogen flow in the global terrestrial system is restricted to the plant-micro organism-soil system; only 5 % of the total flow is concerned with exchanges to and from the atmosphere and the hydrosphere.

Iron and aluminium as cementing substances of soil aggregates

Abstract: Summary Extraction of five soils with acetylacetone in benzene does not change their particle-size distribution, compared with no pre-treatment or dispersion, but it decreases the water stability of soil aggregates. The decrease is closely related to the extent of the extraction of iron and aluminium by acetylacetone in benzene from soils. The metals extracted by acetylacetone are essentially bound to the organic matter. It is suggested they behave as junctions of a net composed of polymeric chains of soil organic matter. The mesh, which exerts a protective action on soil aggregates, is weakened at the junctions of polymeric chains after the removal of metals so that the stability to the disrupting action of water is decreased.

Soil profile development in some alluvial deposits of eastern New South Wales

Abstract: Soil profile data from river terrace sequences on the New South Wales coast and southern highlands have been summarized. In all sequences the profiles have a progressive increase in soil development from low alluvial benches to flood plains to terraces. The general similarity of soils among these and other alluvial sequences in eastern New South Wales is the basis of a descriptive generalization in terms of five profile stages: stratic stage on low alluvial benches; cumulic stage on flood plains; low-contrast solum stage on low terraces; high-contrast solum stage on high terraces; extended subsolum stage on highest terraces. Sufficient lack of correlation occurs between sequences to suggest that the profile stages are groupings within a continuous spectrum of profile variation, the whole representing the one pedogenetic pathway. Pedogenesis in these alluvial landscapes is considered to progress through the development, first of a biotic profile which reaches a maximum within 1000 years, which is then degraded with the onset of mineral weathering and B horizon development, to a maximum solum form within 30 000 years. The rates of change of biotic and mineral profile components are sufficiently slow that only broad limits of confidence can be applied to soil stratigraphic correlations based on field morphology alone.

Ethylene production by bacteria in reduced microsites in soil and some implications to agriculture

Abstract: Ethylene, produced by spore-forming bacteria in anaerobic microsites, is a critical regulator of microbial activity in soil. It has a central role in a self-regulating microbial cycle in soil with important implications for rates of turnover of organic matter, availability of plant nutrients, and incidence of soil-borne plant disease. Recognition of the presence of numerous anaerobic microsites, especially in the rhizosphere. is the key to understanding ethylene formation in field soils. These microsites may also affect directly the availability of plant nutrients in soil, and this is discussed. Nitrate nitrogen stops ethylene production in soil by poising the redox potential. Similarly, it may interfere with uptake of plant nutrients. This calls for a reappraisal of the supposed benefits of nitrification in agriculture.

Reactions between metals and humified organic matter

Abstract: Summary We studied the properties of the soluble and dispersed compounds of Cu, Mn, Co, Ni, Pb, Zn, and Cd formed by the action of aerobically decomposing plant matter on the respective metal oxides. The metals were mobilized partly in association with colloidal humified organic matter, and partly in true solution as complexes that seemed to be anionic. In the presence of a clay soil there was no net mobilization of colloidally bound Cu, but the dialysable Cu complex was not appreciably sorbed by the mineral colloids and was leached from the reaction mixture. The metals were not precipitated under alkaline conditions from the dialysable complex forms. Material with similar complexing properties was found in the dialysable fractions of a soil organic matter extract, of water squeezed from a raw peat, and of laboratory lysimeter solutions from a podzol under Calluna. Below about pH 6 the exchange of Cu on a soil clay was not affected by the presence of colloidal decomposition products of lucerne. With Co, Ni, and Zn the corresponding pH value was about 4, and the critical value for Cu in the presence of colloidal soil organic matter was also about 4. Below these values the metal and organic matter sorption curves were diametrically opposed so that under these conditions Cu is apparently not strongly bonded to colloidal organic matter.

Surface charge characteristics of six weathered soils from tropical north Queensland

Abstract: Electrochemical studies on 18 samples from six weathered soils from tropical north Queensland showed that they contain colloids of largely the 'constant surface potential' type, i.e, their surface charge is controlled by the pH and ionic strength of the ambient medium. The point of zero charge (PZC), as well as the net charge at the soil pH and pH 7.0 at two electrolyte concentrations, were established. The implications with respect to cation exchange capacity, base saturation, buffer capacity, and water dispersible clay, and the importance of these properties to soil classification and agricultural management, are discussed.

The uptake of zinc-65 by oats in relation to soil water content and root growth

Abstract: Effects of water content of the topsoil on root growth and 65Zn absorption by oats were measured. Seminal roots of oats grew through a labelled uptake layer that had been initially wetted to various water contents. The uptake layer was separated from adjacent layers of wet sand or soil by a thin layer of wax. When the uptake layer was wetted initially and allowed to dry during the uptake period, water content affected root growth and 65Zn uptake similarly. 65Zn absorption by unbranched seminal roots decreased linearly as soil water suction increased from 0.3 to 5 bar. Nevertheless significant amounts of 65Zn were absorbed (40% of that from wet soil) even when the soil water suction exceeded 15 bar, with negligible concomitant uptake of water. Provided the roots had access to water in a subjacent layer, rates of 65Zn absorption from dry soil increased with the age of the plants. The exudation of mucilage from the root was enhanced locally where the soil was dry. The mucilage may facilitate the transfer of zinc to the root in dry soil.

Competition for plant nutrients in soil; a theoretical approach

Abstract: A mathematical model of whole plant growth in soil is presented. Particular emphasis is given to those factors which relate to the absorption of nutrients and water by the root system. There are two basic premises; that a plant is made up of two pools, structural material and precursors to structural material, and that structural material is produced by a reaction between a given ratio of precursors. The precursors are soluble carbohydrate and unbound nitrogen, probably nitrate. Increase in leaf area and root length is a consequence of absorbed nitrogen combining with photosynthate.The absorbing power and the distribution throughout the soil of the roots is controlled, through feedback mechanisms, by the ratio of the precursors, within the plant. The description of plant growth is interfaced with a model of one-dimensional flow of water and solutes in soil, and gives a model for investigating plant growth, or competition between root systems of more than one plant. The results of a number of simulations are presented. A sensitivity coefficient is defined to compare the effect of various properties on overall growth. Its value is calculated for 11 plant properties. It is some measure of the competitive advantage conferred on the plant by a change in the value of each property. The results of the competition experiments are given as replacement diagrams.The model has weaknesses. Because it is explicit, it defines in precise detail the experiments which would support the hypotheses, or suggest modifications to them. As a holistic analysis, it brings together ideas from different disciplines into one comprehensible framework.

Effect of artificial weathering cycles on the structural stability of a dispersed silt soil

Abstract: Summary A very fine sandy loam soil was severely puddled in the laboratory and subjected to varying numbers of freeze/thaw-wet/dry cycles in an attempt to restore its original level of structural stability. After only three cycles the stability of the treated soil reached its maximum value, which was slightly greater than that of untreated soil collected from the field. A higher level of soil organic matter was accompanied by an increase in structural stability as determined by the dispersion ratio technique and a technique involving partial dispersion in Calgon.

Chemical evaluation of vegetables grown with conventional or organic soil amendments

Abstract: Garden vegetables were grown with “organic”; or “commercial”; fertilizer amendments to the soil. Plot preparation and other general cultural practices were identical. Tomatoes, potatoes, peppers, lettuce, onions and peas were planted, and leaf tissue and edible produce were harvested. N, P, K, Ca and Mg and content of ascorbic acid were determined in some of the produce. Certain vegetables were evaluated by a trained taste panel for palata‐bility differences. Generally, the conventional plots produced more yield of vegetables, although seasonal variation was greater than variation due to soil amendments. Mineral content was essentially the same from both regimes. The taste panel preferences were not consistent. From these data, it was concluded that the two methods of vegetable production were equal for quality and nearly equal for yield over the two years.

INFLUENCE OF SOIL PROPERTIES ON ADSORPTION OF PESTICIDE-DERIVED ANILINE AND p-CHLOROANILINE

Abstract: Summary Soil properties were significantly related to the adsorption of aniline and p-chloroaniline, greater adsorption always occurring with p-chloroaniline Multiple regression analysis indicated that the organic matter plus available water (or clay) was better than the simple linear relationship, with organic matter alone The resulting equations accounted for most of the variability in aniline or p-chloroaniline adsorbed (R2= 0·92 and 0·94, respectively) The contribution of organic matter to the adsorption was calculated as 79 and 77 per cent for aniline and p-chloroaniline Experimental data on partially oxidized soils emphasized the major role played by soil organic matter The variability in adsorption was mainly due to the organic matter left after oxidation (R2= 0·72 and 0·64 for aniline and p-chloroaniline) No other combinations of variables significantly improved these relationships

Extraction of metals from basalt by humic acids

Abstract: IN many studies, the activity of humic acid in weathering and other geological processes has been considered negligible. Only simple, low molecular weight organic acids are usually considered effective in mineral degradation1. Those acids, however, frequently constitute only a minor fraction of the soil organic matter, particularly in semi-arid and arid areas. In Israel, fulvic acid/humic acid ratios in the organic matter of major soil types range, with one exception, from 1.5 to 6 (ref. 2). Humic acids are also well represented in the organic matter of many sediments3,4. The effect of these high molecular weight compounds on mineral decomposition and metal dissolution is therefore of great interest in the earth sciences. The results presented here suggest that humic acids also may have a significant role in rock solubilisation and weathering, because of their capacity to extract considerable amounts of metals, particularly copper and zinc, from basalt rock.

Organic sulphur fractions in scottish soils

Abstract: Over 90% of the sulpher in some acid surface soils derived from different parent materials in north-east Scotland was in organic combination. N:S ratios in the majority of the soils fell within the narrow limits of 6.0–7.5, and showed less variation than C:S ratios. Organic sulphur was poorly correlated with organic phosphorus, and high correlations with categories of soluble aluminium and iron seemed to reflect similar relationships between these elements and the whole organic matter. A group of calcareous soils derived from shelly sand deposits contained a lower proportion of organic sulphur. An average 64% of organic sulphur in the acid soils occurred as organic sulphate, compared with only 23% in the calcareous soils. Organic sulphate was less well correlated with carbon and nitrogen than was total organic sulphur. Total carbon-bonded sulphur was best determined as the difference between total organic sulphur and organic sulphate, because direct measurement by Raney-nickel reduction underestimated the amount present in most of the soils, due to the presence of chemically unreactive compounds. Good correlations between the reactive carbon-bonded sulphur and carbon, nitrogen and organic sulphur, suggested that a well-defined group of compounds was being measured. There were no consistent effects of drainage conditions on organic sulphur contents, or on the amounts and proportions of organic sulphur present as sulphate or in carbon-bonded form. The freely drained soils derived from basic igneous drift, however, contained more organic sulphur than poorly drained samples, but this is attributed to differences in the organic matter content. Several features of the results indicated that organic sulphur, unlike organic phosphorus, was predominantly an integral part of the soil organic matter.

The Significance of Intercalary Ammonium in Representative Surface and Subsoils from Southern New South Wales

Abstract: Six surface and subsoils known to contain native intercalary ammonium were examined to assess the importance of ammonium fixation when nitrogen fertilizers were applied, the availability of native and recently fixed intercalary ammonium to plants, and the effect of potassium on fixation. Only one soil, a grey soil of heavy texture (Ug 5.4), fixed significant amounts of added ammonium sulphate, the level of intercalary ammonium being increased by 55 % in the surface and 100% in the subsoil. The native level of intercalary ammonium was reduced by 8 and 17% by the growth of plants in the red-brown earth (Dr 2.23) and the grey soil of heavy texture, respectively, but was unchanged in the other soils. The addition of small amounts of potassium prior to the ammonium did not affect fixation; however, additions of 500 ppm reduced the fixation of a 200 ppm solution of ammonium by 80 %. Intercalary ammonium is not considered to be important in the nitrogen economy of five of the six major farming soils of the slopes and plains area of southern New South Wales. The sixth, the grey soil of heavy texture, is an alluvium associated with the Murrumbidgee River and its tributaries, and as such is used extensively for irrigated agriculture. Because this soil can fix large amounts of ammonium, the use of ammonium or ammonium forming fertilizers is not recommended.

Isotopic studies of the nitrogen balance in a cracking clay. III. Nitrogen recovery in plant and soil in relation to the depth of fertilizer addition and rainfall

Abstract: 15N-labelled nitrate nitrogen was added at either 15 cm or 45 cm depth to 10-cm diameter undisturbed cores of black earth soil. Cores were either fallowed or planted to wheat and received either 444 mm or 255 mm of simulated and natural rain during a 17-week growing season under field conditions. Between 92 and 98 % of added 15N could be accounted for in planted or fallow cores receiving the lower rainfall, while those receiving the higher rainfall contained 75-94 %. The loss was larger where fertilizer was added at 15 cm than at 45 cm depth. Fallow cores lost more 15N than planted cores. These losses are ascribed mainly to denitrification and are discussed in relation to the results of earlier work with this particular soil-plant system. Plants yielded more, and recovered more of the fertilizer nitrogen, in those cores which received the higher rainfall. Plants recovered more applied nitrogen from 45 cm depth than from 15 cm depth. At harvest, over 40% of the applied nitrogen remained as nitrate in the planted cores which received the lower rainfall. In these cores, only 38-47 % of the fertilizer was recovered in plant tops. The significance of these results for fertilizer efficiency is discussed.

The extraction and definition of non-exchangeable or fixed ammonium in some soils from southern New South Wales

Abstract: The amounts of non-exchangeable or fixed NH4+ in six soils from southern New South Wales were determined by using three methods. Using a potassium hydroxide pretreatment 2-13 % of the total nitrogen in the surface soils was fixed and between 16 and 33 % in the subsoils. Different methods showed up to a threefold difference in the amount on some soils and non-significant differences in others. The interpretation of the part played by this fraction of soil nitrogen in the chemical and biological equilibrium of soil must be qualified according to the extraction method used. The use of soil samples having a larger particle size (< 2 mm) than previously used (<0.147 mm) was found to be adequate with the soils studied. As the present definition of non-exchangeable or fixed NH4+ is misleading, it is proposed that this fraction of soil nitrogen be called intercalary ammonium (NH4+). Intercalary NH4+ is defined as that nitrogen recovered from within clay minerals by hydrofluoric-hydrochloric acid treatment, subsequent to a potassium hydroxide or potassium hypobromite/potassium hydroxide pretreatment and 0 . 5N potassium chloride leaching to remove exchangeable NH4+ and organic nitrogen from the outside of the clay particles.