Showing papers on "Soil organic matter published in 1982"

HUmus Chemistry Genesis, Composition, Reactions

Abstract: Partial table of contents: Organic Matter in Soils: Pools, Distribution, Transformations, and Function. Extraction, Fractionation, and General Chemical Composition of Soil Organic Matter. Organic Forms of Soil Nitrogen. Native Fixed Ammonium and Chemical Reactions of Organic Matter with Ammonia and Nitrite. Organic Phosphorus and Sulfur Compounds. Soil Carbohydrates. Soil Lipids. Biochemistry of the Formation of Humic Substances. Reactive Functional Groups. Structural Components of Humic and Fulvic Acids as Revealed by Degradation Methods. Characterization of Soil Organic Matter by NMR Spectroscopy and Analytical Pyrolysis. Structural Basis of Humic Substances. Spectroscopic Approaches. Colloidal Properties of Humic Substances. Electrochemical and Ion-Exchange Properties of Humic Substances. Organic Matter Reactions Involving Pesticides in Soil. Index.

Changes in Inorganic and Organic Soil Phosphorus Fractions Induced by Cultivation Practices and by Laboratory Incubations

Abstract: Changes in inorganic and organic phosphorus (P) fractions resulting from 65 years of cropping in a wheat-wheat-fallow rotation were studied using a sequential extraction technique. Total P content of the cultivated soil was 29% lower than that of the adjacent permanent pasture; the major loss of P (74% of total P lost) was organic P and residual P. Of the total P lost, 22% was from the extractable organic P forms, whereas 52% originated from stable P.Incubation studies were used to study seasonal P transformations during simulated fallow with and without residue incorporation and P fertilization. Nine monthly additions of cellulose (765 µg C · g−1 soil) with and without P (9 µg · g−1 soil) significantly altered levels of total extractable organic P and inorganic P in incubated soils. Evidence is provided for microbial activity playing a major role in redistributing P into different forms in the soil

Soil carbon pools and world life zones

Abstract: Soil organic carbon in active exchange with the atmosphere constitutes approximately two-thirds of the carbon in terrestrial ecosystems1,2. The relatively large size and long residence time of this pool (of the order of 1,200 yr) make it a potentially important sink for carbon released to the atmosphere by fossil fuel combustion; however, in many cases, human disturbance has caused a decrease in soil carbon storage3,4. Various recent estimates place the global total of soil carbon between 700 (ref. 2) and 2,946 × 1015 g (ref. 5) with several intermediate estimates: 1,080 (ref. 1), 1,392 (ref. 6), 1,456 (ref. 3), and 2,070 × 1015g (ref. 7). Schlesinger's3 estimate seems to be based on the most extensive data base (∼200 observations, some of which are mean values derived from large studies in particular areas) and is widely cited in carbon cycle studies. In addition to estimating the world soil carbon pool, it is important to establish the relationships between the geographical distribution of soil carbon and climate, vegetation, human development and other factors as a basis for assessing the influence of changes in any of these factors on the global carbon cycle. Our analysis of 2,700 soil profiles, organized on a climate basis using the Holdridge life-zone classification system8, indicates relationships between soil carbon density and climate, a major soil forming factor. Soil carbon density generally increases with increasing precipitation, and there is an increase in soil carbon with decreasing temperature for any particular level of precipitation. When the potential evapotranspiration equals annual precipitation, soil carbon density9 is ∼10 kg m−2, exceptions to this being warm temperate and subtropical soils. Based on recent estimates of the areal extent of major ecosystem complexes9,10 which correspond well with climatic life zones, the global soil organic carbon pool is estimated to be ∼1,395 × 1015g.

The Storage and Production of Organic Matter in Tropical Forests and Their Role in the Global Carbon Cycle

Abstract: To investigate the storage relationships between and production of organic matter in tropical forests and climate, data on forest biomass, soil organic matter, litter storage, primary production, and litterfall were surveyed from the literature and organized using the Holdridge Life Zone system of classification. Ordinary least squares regressions were applied to all the data sets using the ratio of temperature to precipitation (T/P) as an index to climate and the independent variable. Total forest biomass (40-538 t/ha) gave a significant inverted U-shaped relationship with T/P, with peak values in the tropical moist forest life zone and lower ones in wetter and drier forest life zones. Soil carbon content (24-599 t C/ ha) decreased exponentially and significantly with increasing T/P (i.e., from wet to dry forest life zones). No significant relationship was found between litter storage and T/P. Gross primary production (19-120 t/ha yr) decreased curvilinearly and significantly with increasing T/P. Neither net primary production (11-21 t/ha yr) nor wood production (1-11 t/ha yr) were related to T/P. The ratio of leaf litter production to net primary production (0.25-0.65) was inversely related to T/P, suggesting different strategies of allocation of the net primary production in different life zones. The relationship between total litterfall (1.0-15.3 t/ha yr, excluding large wood) and T/P was significant and its shape similar to that obtained for biomass versus T/P; litterfall was highest in tropical moist forest life zones and lower in wetter or drier ones. The linear relationship between biomass and litterfall suggested that the turnover time of biomass in mature tropical forests is similar for all life zones, and is of the order of 34 yr. To determine the role of tropical forests in the global carbon cycle, literature estimates of areas of tropical forests were placed into six life zone groupings. The total tropical and subtropical basal and altitudinal forest area of 1838 million ha was comprised of 42 percent dry forest, 33 percent moist forest, and 25 percent wet and rain forest life zone groups. Organic-matter storage data were also combined into the six life zone groups and the means for each group calculated. The product of forest areas in the six groups and the mean organic matter per unit area in the groups yielded a total storage of 787 billion t organic matter, with vegetation accounting for 58, soils 41, and litter 1 percent. About half of the total storage was located in the tropical basal wet, moist, and dry forest life zone groups. Litterfall data were treated in the same way as organic-matter storage, resulting in a total litter production in tropical forests of 12.3 billion t organic matter/yr. Most litter was produced in the tropical basal moist forest group (30%) and least in the tropical basal dry forest group (10%). Turnover time of litter in tropical forests was less than 1 yr. Lowest turnover times were in very wet (1 yr) and in dry (0.9-1.9 yr) life zone groups. Tropical forests play an important role in the global carbon cycle because they store 46 percent of the world's living terrestrial carbon pool and 11 percent of the world's soil carbon pool.

World Patterns and Amounts of Terrestrial Plant Litter Production

Abstract: Leaf and total plant litter amounts worldwide are estimated by climatic curve-fits and mapped by computer using a world climatic data base Computer planimetry of the maps produced estimates of yearly terrestrial leaf litter (351 x 10 to the power of 9t) and total litter production (548 x 10 to the power of 9t) This is about 13% and 20% respectively, of the estimated world totals of detrital soil organic matter (Refs 20)

Emissions of nitrous oxide from soils

Abstract: Potential changes in the concentration of nitrous oxide (N2O) in the atmosphere have sparked considerable interest because of the proposed role of N2O in regulating stratospheric ozone levels, and in contributing to the atmospheric greenhouse effect. A substantial portion of the atmospheric N2O is thought to result from microbial transformations of inorganic forms of nitrogen in soils; N2O is an intermediate in denitrification (reduction of NO−3 to N2) and is formed during nitrification (oxidation of NH+4 to NO−3) in soils, although the mechanism is unclear. Several models have predicted that input of nitrogen into cropland, either from commercial fertilizers or N-fixing leguminous crops, could sufficiently increase emissions of N2O from soils to deplete stratospheric ozone levels1–3 and raise average world temperatures4. We report here N2O emissions from mineral and organic soil sites in New York and from organic soil sites in the Florida Everglades Agricultural Area.

The distribution of carbon and the demand of the fungal symbiont in leek plants with vesicular-arbuscular mycorrhizas

Abstract: SUMMARY Leek plants (Allium porrum) were grown on partially sterilized soil either inoculated (M) or not (NM) with the vesicular-arbuscular mycorrhizal fungus, Glomus mosseae. They were pulse-fed with 14CO2 in an apparatus which allowed CO2 subsequently respired either by the shoots or by the roots plus soil to be separately monitored. There were three experiments. In two, plants were harvested 48 h after labelling and in the third after 214 h. At harvest, the distribution of 14C between shoot, root, soil organic matter and root washings was measured. Similar growth curves for M and NM plants were obtained by supplying extra phosphorus to the latter, so that C distributions for both treatments could be compared directly. In all three experiments, about 7 % more of the total fixed C was translocated from shoot to root in M plants compared to NM plants. In the third experiment, this extra translocate could be accounted for by increased root respiration plus increased loss of C to the soil but, despite this drain, M and NM plants had equal rates of C assimilation per unit of leaf area. However, shoots of M plants had a lower content of dry matter and hence higher assimilation rates expressed on a dry matter basis. Increased hydration is suggested as a mechanism whereby leaf area and hence C assimilation increases in mycorrhizal plants and which offsets the effects of the drain imposed by the mycorrhizas.

Organic matter production and distribution in slash pine (pinus elliottii) plantations

Abstract: The production and accumulation of total system organic matter (to 100 cm soil depth) in plantations of slash pine were analyzed using three replications of stands 2, 5, 8, 14, 18, 26, and 34 yr old. Maximum leaf area occurred at 5 yr. After this point aboveground net primary production (NPP) continued to increase to a maximum at 26 yr and then declined. After 5 yr stem biomass production composed a constant 50% of NPP. The forest floor increased at a constant rate through 34 yr, although total detritus (forest floor plus soil organic matter) was relatively constant at m160 Mg/ha. Live vegetation mass was less than detritus mass until =m25 yr, the current harvest rotation length. Total system organic matter showed no indication of a decline after site preparation, and was still increasing at 34 yr (340 Mg/ha). During site preparation -30 Mg/ha organic matter were lost through burning and decomposition. This loss was small enough to be completely offset by increases in live vegetation and forest floor over -3 yr following site preparation, which may be important in limiting losses of nutrients from these sites after a disturbance. rently 5.2 x 106 ha of commercial slash pine (Pinus elliottii var. elliottii), with -40% of the total in north- ern Florida. Fifty-two percent of the total is in plan- tations, representing 14% of the forested land area in Florida, and the rest is in naturally regenerated second growth (Scheffield et al. 1981); the proportion in plan- tations is rapidly increasing. Although the conversion of the natural stands to plantations amounts to landscape modification at a tre- mendous scale, we have little idea of the ecological consequences. Delcourt and Harris (1980) proposed

Bound pesticide residues in soil and plants.

Abstract: To assess the environmental significance of pesticide1 residues in soil and plants one must distinguish between two types of residues: those that are extractable with solvents and those that are not extractable with solvents Bound pesticide residues are basically those residues remaining in soil or plants after exhaustive solvent extraction These residues would escape detection in the analytical procedures conventionally used in residue analysis

Effect of barley plants on the decomposition of 14C‐labelled soil organic matter

Abstract: Summary The effect of barley plants on the rate of decomposition of soil organic matter over a 6-week period was studied using soil that had been previously labelled by incubation with 14C-labelled ryegrass for 1 year. The plants reduced the loss of 14CO2, from soil by 70 per cent over 42 days. About half of the reduction was accounted for by the uptake of labelled C by the plant roots, very little 14C label being associated with the shoot. Chemical fractionation of the root showed that the 14C was chemically incorporated into cell wall materials such as cellulose and holocellulose. The reduction in organic matter decomposition in the presence of plants has been explained by earlier workers in terms ofa reduction in microbial activity as a result of a soil moisture deficit caused by plant transpiration. This explanation does not account for all the reduction in decomposition noted in the present experiments. Control soil (without a plant, but amended with glucose or yeast extract to simulate the effect of root exudates) showed a small positive priming effect, the release of 14CO2, being increased. Thus the mechanism by which plants conserve organic matter is complex and cannot be explained merely by analogy to an increased level of nutrients available for microbial metabolism.

Effects of cover crops on soil structure and on yield of subsequent arable crops grown under strip tillage on an eroded alfisol

Abstract: Effects of weed fallow and of three grasses and five leguminous cover crops were investigated on soil structure of an eroded Alfisol. Crop growth and yields of subsequently grown arable crops were assessed under strip-tillage through the mechanically or chemically suppressed sods. Cover crops and fallowing improved soil organic matter content, total N, water retention and transmission properties, and decreased bulk density only in the top 0–10 cm depth. The improvements rendered were, however, slight. Grasses were difficult to suppress with paraquat or mechanical mowing, which resulted in low or negligible yield of maize, cowpea, and cassava. Leguminous covers were easily suppressed with paraquat application, and resulted in good yield of maize and cowpea. Mechanical mowing was as successful as herbicide application for suppressing Stylosanthes guianensis and resulted in satisfactory yield of maize and cowpea. Yield of cassava tubers was extremely low due to shallow surface soil, compacted sub-soil horizons, and competition from weeds and regrown cover crops. Results are discussed in terms of the amelioration of eroded and degraded soil.

The Effect of Carbon Mineralization on Denitrification Kinetics in Mineral and Organic Soils

Abstract: Rates of denitrification and organic carbon (C) mineralization were measured simultaneously in soil suspensions maintained at 30°C under anoxic conditions. Nine mineral and seven organic soils were used in the study. Disappearance of NO3~ and production of CO2 were measured at various times during the 12-day incubation. Labeled NO, was used to differentiate denitrification from immobilization and reduction to NH4-N. The rate of organic C mineralization followed first-order kinetics in all soils with the mineralization rate coefficient (kc) values varying from 0.075 to 0.405 day'. The denitrification rates in anaerobic soils were shown to be proportional to the concentration of the two substrates: NO, and available C. The denitrification rate coefficient (&„) value was essentially constant for the mineral soils [0.00147 ± 25% day" (fig C/mi)"], while kn values for the organic soils were somewhat more variable [0.00155 ± 65% day" (jig C/ml)"']. Significant correlations were observed between NO," consumption and CO, production. The molar ratio of NO, consumption to CO, production ranged from 0.6 to 1.8. Significant relationships were also observed between water-soluble C (WSC) and total organic C (TOC), maximum available C (C^,,), and WSC and Cmls, respectively. Watersoluble C represented 0.4 to 0.9% of TOC, while Cm represented about 0.6 to 1.4% of TOC. Results also showed that denitrification rates were influenced by the rate at which available C is mineralized and made available to the organisms. Additional Index Words: nitrate reduction, water-soluble carbon, first-order kinetics, anaerobic soil, flooded soil, Michaelis-Menton kinetics. Reddy, K. R., P. S. C. Rao, and R. E. Jessup. 1982. The effect of carbon mineralization on denitrification kinetics in mineral and organic soils. Soil Sci. Soc. Am. J. 46:62-68. T ROLE of organic carbon (C) as an electron donor in the denitrification process has been widely recognized. Several researchers (Wijler and Delwiche, 1954; Bremner and Shaw, 1958; Nommik, 1956; Bowman and Focht, 1974; Reddy et al., 1978) have shown increased denitrification rates following the addition of energy source (organic C) to a soil. Significant relationship was reported between NOf losses via denitrification and "available" C, as evaluated either by glucose-equivalent C (Stanford et al., 1975a), by watersoluble C (Burford and Bremner, 1975; Reddy et al., 1980), or by mineralizable C (Burford and Bremner, 1975). A considerable portion of available C would be used in normal oxidative respiration by denitrifiers and 1 Florida Agric. Exp. Stn. Journal Series no. 2,902. Received 15 Jan. 1981. Approved 31 Aug. 1981. 2 Assistant Professor, Agric. Res. and Ed. Cen., Univ. of Florida, Sanford, Fl 32771, and Assistant Professor and Scientific Programmer, 'respectively, Soil Sci. Dep., Univ. of Florida, Gainesville, FL 32611. other microorganisms (using O2 as an electron acceptor) until the system becomes anoxic. When O2 is depleted from the system, the denitrifiers use NO3~ as an electron acceptor during their oxidative respiration. Once the easily decomposible C is used by the denitrifiers, the rate of NO3~ loss would depend on the rate of soil organic C conversion to mineralizable organic C and to soluble organic C (Focht and Verstraete, 1977), while C loss in the same system may not depend on the availability of NO3~, because some organisms use Fe, Mn, and SO4 as their electron acceptors during C oxidation. Denitrification rates, expressed either as zero-order (Wiljer and Delwiche, 1954; Nommik, 1956; Patrick, 1960; Reddy et al., 1978) or first-order (Stanford et al., 1975a; Reddy et al., 1980) rate coefficients, and which do not account for the soluble soil organic C availability will be specific to the soil and a given set of environmental conditions, and not of general value in modeling the denitrification process. Also, most researchers (Stanford et al., 1975a; Bowman and Focht, 1974; Burford and Bremner, 1975; Kohl et al., 1976) measured denitrification rates under static conditions where NO3~ was present in the overlying water and the underlying soil. Since denitrification occurs only in the anaerobic soil layer, diffusion of NO3~ from the floodwater to the anaerobic soil layer also controls the rate of denitrification (Reddy et al., 1978). No data are available to date on the kinetics of available C mineralization coupled with the kinetics of denitrification measured under diffusion nonlimiting conditions. The objectives of the present investigation were (i) to determine simultaneously the rates of denitrification and C mineralization in several mineral and organic soils; (ii) to develop a relationship between the kinetics of denitrification and organic C mineralization; and (iii) to obtain a denitrification rate coefficient as a function only of available C (i.e., independent of soil type). REACTION RATE EQUATIONS In this study, the rate of available C mineralization during denitrification was assumed to follow first-order kinetics:

Phenolic Compounds in Soil as Influenced by the Growth of Different Plant Species

Abstract: (1) The amounts of six phenolic compounds (p-hydroxybenzoic, vanillic, p-coumaric and ferulic acids, p-hydroxybenzaldehyde and vanillin), released by four extractants, differed considerably between soils from fourteen plots on which four graminaceous species, eight dicotyledonous species and two species of the Pteridophytes had been grown individually for 16 yr. There were also large differences in the amounts of the phenolic compounds extracted from the roots of these species. (2) When expressed in terms of #g phenolic compound g-1 organic C, differences between the roots were greater than differences between the soils. Also the amounts extracted by water from the roots (after freeze-drying and grinding) were much greater than the amounts extracted from the soils. The amounts extracted by 2 M NaOH were, in general, greater from the roots than from the soils and, with p-coumaric and ferulic acids from the graminaceous species, much greater. However, in instances where the amounts extracted from the roots by 2 M NaOH were small, e.g. vanillic acid from Pteridium aquilinum, the amounts from the soils, expressed per unit of organic C, were greater than those from the roots. (3) The sum of the six phenolic compounds extracted from the soils by 2 M NaOH represented between 0-03% and 0.33% of the soil organic matter, these values referring to soils under Pteridium aquilinum and Campanula rapunculoides respectively. In thirteen of the soils, p-coumaric acid was present in greater amounts than anypof the other compounds. (4) With the possible exception of the soil under Agropyron repens, the amounts of the identified phenolic compounds extracted by water appeared unlikely to exert allelopathic effects. However, the amounts released by 0-5% Ca(OH)2 were equivalent to concentrations in the soil solution that have been reported to have adverse effects on plant growth under certain conditions, which suggests that such effects might occur in the field as a consequence of liming.

Effect of sewage sludge on trace element mobility in soils

Abstract: Adsorption of Be, F, B, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Se, Sr, Mo, Tc, Ag, Cd, Sn, Sb, Cs, Ba, Hg, Pb, Bi, and P was measured in a sandy soil and a sandy loam soil at concentration levels closely corresponding to those to be expected for field conditions. Mobilities of the elements in the soils were calculated from the adsorption data. Of the trace elements studied, F, B, and Tc were found to be very mobile in both the sandy and sandy loam sils. Manganese, Sr, and Sb were highly mobile only in the sandy soil, and Mo in the sandy loam soil. In general, sludge solutions appeared to increase the mobility of elements in a soil. This is due to a combination of complexation by dissolved organic compounds, high background concentrations, and high ionic strengths of the soil solutions. The relative effects of these factors vary strongly among elements. Equations were derived predicting the rates of accumulation in soils and accompanying increases in the soil solutions of trace elements added with sewage sludge. When adsorption was related to soil organic matter content, for many trace elements the strength of adsorption was found to dependmore » only on pH, increasing with increasing pH.« less

Seasonal and spatial variation in fungal biomass in a forest soil

Abstract: Soil fungal biomass, determined by the fluorescein diacetate (FDA) method, was studied during a 3 yr period in three horizons in a mature and a clear-cut pine forest in Sweden with and without slash left on the ground. In the organic soil layer the amount of hyphae showed a similar seasonal periodicity at all three sites, and this periodicity was correlated to the soil moisture content. Such a periodicity was not found in the mineral soil. There were also annual differences in the amount of FDA-active hyphae which might be explained by different climatic conditions. The mean spatial variation in biomass content was 37.9% (coefficient of variation), which was almost as great as was the variation between different sampling dates. Only between 4 and 45% of the total variation in the fungal lengths could be explained by soil moisture and organic matter content.

Soil and litter respiration rates in different microhabitats of a mixed oak-conifer forest and their control by edaphic conditions and substrate quality

Abstract: Soil and litter respiration rates were measured under canopies ofQuercus floribunda, Q. leucotrichophora, Cedrus deodara, Cupressus torulosa and mixed tree species by alkali absorption. The soil and litter samples were analysed for selected chemical characteristics. Soil nitrogen and soil water were positive effectors for soil respiration, while soil carbon and bulk density inversely affected the same. Interactive control of soil respiration by combined effects of edaphic conditions and quality of overlying litter was also indicated. Weight specific litter respiration was positively affected by litter nitrogen and moisture and negatively by lignin. Among the substrate quality parameters, linear combinations of nitrogen, moisture, carbon and lignin explained significant of variability in weight specific litter respiration. A linear combination of litter nitrogen and litter lignin explained 96% variability in weight specific soil plus litter respiration.

Constituents and Properties of Soils

Abstract: Constituents and properties of soils , Constituents and properties of soils , مرکز فناوری اطلاعات و اطلاع رسانی کشاورزی

Electro-ultrafiltration of aqueous soil suspension with simultaneously varying temperature and voltage

Abstract: The procedure of electro-ultrafiltration (EUF) with simultaneously varying voltage and temperature for the determination of nutrient fractions in soil as well as for the characterization of important soil properties such as kind of clay, content of K-selective clay minerals, of CaCO3 etc. is described. The interpretation of the EUF-N, EUF-P and EUF-K fractions is discussed in detail with regard to their availabilities. Moreover the influence of soil properties and soil management on the EUF nutrient fractions is discussed.

Mineralization of Nitrogen in Organic Soils1

Abstract: The effect of fluctuating seasonal temperatures on the release of soluble NO⁻₃-N, NH⁺₄-N, soluble organic N (SON), and solube organic C (SOC) into drainage effluent during soil organic matter mineralization was measured on organic soil profiles obtained intact from various locations in Florida. Soil columns were leached once every 25 days, followed by applying a suction of 100 cm. Soil columns were flooded for 25 days each in the months of July and August to simulate normal agronomic practices. Leachate was analyzed for NO⁻₃, NH⁺₄, SON, and SOC. The amounts of N mineralized ranged from 410 to 938 kg N·ha⁻¹·year⁻¹ for cultivated soils and 874 to 1,250 kg·ha⁻¹·year⁻¹ for virgin soils. Nitrate accounted for 48 to 81% of the total N in the effluent, while SON accounted for about 16 to 45% of the total N. Remaining 2 to 7% of the total N in the effluent was NH⁺₄. Soluble organic C in the leachate accounted for about 1,795 to 3,516 kg C·ha⁻¹·year⁻¹. Seasonal fluctuations in temperatures had minimal effects on the release of SON, SOC, and NH⁺₄, but the release of NO⁻₃ was increased with an increase in average daily temperature (9.4 to 30°C) with Q₁₀ values ranging from 1.3 to 1.9. Flooding the organic soils increased the SON and SOC release into the effluents by about two-fold, compared to drained conditions. Total N loss in 1 year as a result of organic matter mineralization was about 1.3 to 4.2% of the total soil organic N.

Modern and Paleolimnological Evidence for Accelerated Leaching and Metal Accumulation in Soils in New England, Caused by Atmospheric Deposition

Abstract: Empirical field evidence for changing chemical processes in soils caused by atmospheric deposition of pollutants consists of: (1) Long-term water quality data including total dissolved solids, concentrations of specific metals (e.g. Ca), and conductivity; (2) Cation exchange capacity and base saturation values for soils located on precipitation pH gradients; (3) Lysimeter studies; and (4) Chemical analysis of organic soils on precipitation pH and metal gradients. For well-drained organic soils, as precipitation pH decreases, metals are differentially leached at an accelerated rate (Mn > Ca > Mg ≥ Zn > Cd and Na > Al). Experimental field and laboratory lysimeter studies on soil columns yield similar results, with increases in leaching rates for soil solutions with pH = 3 up to 100 × values for soil solutions with pH = 5. Nearly 100% of the Pb from precipitation is accumulating in the organic soil layer or sediments. Zn is accumulating in soils and sediments where the pH’s of precipitation, soil solutions, and surface waters are generally above 5 to 5.5. At lower pH values Zn and other chemically similar elements are desorbed/leached (net) at an accelerated rate.

The comparative significance and utility of the Freundlich and Langmuir parameters for characterizing sorption and plant availability of phosphate in soils

Abstract: In studies using 62 Australian and English soils, the two parameters of the Freundlich sorption equation were compared with phosphate sorption capacity, calculated from the Langmuir 'two-surface' equation, and sorptivity and affinity indices calculated from the simple Langmuir equation applied to an isotherm concentration range of 0-5µg phosphorus/ml. The Freundlich extensive parameter was most highly correlated with sorptivity, and to a decreasing extent with sorption capacity and affinity. It appears to be fundamentally a sorptivity index which reflects the sorption capacity more than the affinity component of sorption, although greatly underestimating sorption capacity. The reciprocal of the Freundlich exponent proved to be an affinity parameter and was most useful in this role on soils of similar sorption capacity. However, conflicting results on different groups of soils showed that this parameter was less distinctive in its role than the others. Studies on two different groups of soils showed that the sorptivity and affinity parameters from the Langmuir equation accounted for more of the variance in plant uptake of labile phosphate than the Freundlich parameters.

Geology, soils and vegetation of Blackhawk Island, Wisconsin.

Abstract: Curtis (1959) showed that both climate and soils influence the composition of Wisconsin forests but he could not determine the relative effects of each. To determine the effects of soil properties on species composition, a wide variety of soil and community types is needed in a single climatic regime. Blackhawk Island is a 70-ha island in the Wisconsin River in southwestern Wisconsin which supports a wide variety of forest communities on several soil types, including some communities and soils usually found only in northern Wisconsin. The soils form a gradient of moisture and N availability. Pines (Pinus strobus L., P. resinosa Ait.) are dominant on sandy soils with low N mineralization and nitrification; oaks (Quercus borealis Michx., Q. alba L.) are dominant on sandy clay-loams and silt loams with moderate N mineralization and nitrification, and sugar maple (Acer saccharum Marsh.) is dominant on silty clay-loams with high N mineralization and nitrification. Species replacement along this gradient results in an increase in continuum index that is strongly related to the increase in N mineralization, nitrification, silt + clay content and P content of the soils, but less strongly related to other soil properties. Two communities not on this gradient are: (1) aspen (Populus grandidentata Michx.) on plowed silt loam with low N mineralization and nitrification and (2) hemlock (Tsuga canadensis (L.) Carr.) on organic soil with low N mineralization and nitrification. The soil textures are a result of the geologic history of the island. The distribution of communities is therefore a result of ecological processes which are working within the framework of a soil texture gradient determined by the geologic history of the island. INTRODUCTION In a gradient analysis of the vegetation of Wisconsin, Curtis and his co-workers (Curtis, 1959; see Literature Cited for further references) showed that the geographical distribution of species and communities throughout the state was related to both climate and soil. Because of the large geographic area covered and because of the relationship between climate and soils, it was difficult to determine which had more influence on the distributions and community relationships of species. Many factors varied along a climatic gradient from southwestern to northeastern Wisconsin. For example, the distribution of communities was similar along both a pH gradient and a mean July temperature gradient because of coincident but independent changes in bedrock chemistry and July temperature. In addition, the importance of several species in the communities, such as sugar maple, increased with both decreasing temperature and increasing soil moisture. More recently, Peet and Loucks (1977) showed that the composition of southern Wisconsin forests is related to a moisture-nutrient gradient and to a successional gradient, but did not specify the important nutrient(s) involved. In order to determine more precisely the effect of soils or climate on vegetation distribution, it is desirable to find sites in which one of the factors is held constant, or nearly so, while the other varies. The purpose of this paper is to examine changes in species composition of several forests along a gradient of soil types under equivalent climatic conditions.

Characterization of soil structure and stability using modulus of rupture - exchangeable sodium percentage relationships

Abstract: Measurements of the modulus of rupture (MOR) and in particular of the way in which it changes for a given soil with change in exchangeable sodium percentage (ESP) from zero to 20, have been used to characterize the structural stability of a range of soils from the Western Australian wheat-belt. For convenience soils were categorized as hard-setting or non-hard-setting by an arbitrary choice of an MOR value of the natural soil of 60 kPa as the lower limit of the hard-setting behaviour. The most striking differences between the two soil categories are the higher soil strength at zero ESP (baseline MOR) and rapid increase in MOR with increasing ESP (sodium sensitivity) generally characteristic of the hard-setting soils compared with the non-hard-setting soils. The MOR values quantitatively evaluate the tendency of the soils to slake on wetting, and the sensitivity of the MOR to increasing ESP (as a result of increasing double layer swelling forces) illustrates the extent and permanency of the stabilizing bonds in the soil matrix. The presence of exchangeable magnesium on the exchange sites has been shown to increase the MOR values compared with those for exchangeable calcium at all ESP values in line with previous evidence of the deleterious effects of this cation on soil structure. Although more detailed studies are required, the value of this approach is illustrated by its apparent ability to differentiate clearly between the effects of different management techniques (e.g. continuous cultivation as against continuous cropping), and even between short term effects arising within 1/1 rotations. The results from the 'paired' sites where soils, similar in most respects and having undergone identical management, exhibit significant differences in sodium sensitivity of their MOR, suggest that the strength and longevity of structural bonds may be related to the nature of the exchangeable cations present (in particular, whether sodium or calcium dominate) at the time of incorporation of organic matter in the soil.

Soil Morphology and Distribution of Iron and Sulfur Fractions in a Coastal Flood Plain Toposequence

Abstract: A transect of soils across a toposequence on the coastal flood plain of the Shoalhaven River (N.S.W.) was described. The toposequence comprised a backswamp, toe of levee, and levee, and was underlain by a pyritic estuarine deposit. The development of an acid sulfate horizon along the toposequence was related to drainage as influenced by the topography. The backswamp profile had no acid sulfate horizon, whereas the soils of the toe of levee had well-developed acid sulfate horizons. The levee profiles had thin acid sulfate horizons. The distribution and form of the products of oxidation of the pyritic deposit were studied in profiles of each topographic unit by chemical fractionation of soil iron and sulfur. The levee soil showed marked redistribution of iron within its profile. Its acid sulfate horizon contained little jarosite, and its pH was higher than that found in the well-developed acid sulfate horizon of the toe of the levee soil. The latter horizon contained up to 24.3 m.e. sulfur/100 g as jarosite and had pH values near 3.9. The backswamp profile had little iron redistribution, and the estuarine sediment had been only partially oxidized. The distribution of various iron and sulfur fractions and soil pH, were discussed in relation to the oxidation of the pyritic sediment, migration of Fe2+, long term movements in the water table, hydrolysis of jarosite to free iron oxide under the influence of accreting alluvium, and periodic surface flooding.

Vertical distribution of organic matter in eight vegetation types near Eagle Summit, Alaska

Abstract: The amount and distribution of organic matter was measured in different categories in six montane tundra vegetation types in a snow accumulation area and in tussock and intertussock areas in Eriophorum vaginatum tussock tundra in central Alaska. In root properties, the tussock and intertussock areas were more similar to the fellfield zone than to the vegetation zones below the snow accumulation area. Root density apparently increased as soil nutrients decreased, but this increase may be caused by higher soil moisture and higher root relative water content. The tussock tundra has accumulated more dead soil organic matter than any of the montane zones.

Field studies of water and salt movement in an irrigated swelling clay soil. I. Infiltration during ponding

Abstract: Infiltration and deep percolation were measured during ponding of a saline sodic cracking clay soil, commonly used for rice production in the Riverina of New South Wales. Because gypsum may be used to ameliorate this soil for row cropping, the effect of incorporating gypsum into the plough layer was determined. Without gypsum, 292mm water infiltrated in 379 days of ponding, wetting the profile to approximately 2.1 m. In contrast when gypsum was incorporated in the plough layer, 605 mm of water infiltrated in 145 days, and water had penetrated beyond 4.5 m in 57 days. In the latter case, sufficient water percolated below 2.0m to raise the groundwater level by as much as 10m. The infiltration rate for the unameliorated soil was similar to values determined by others; for the ameliorated soil, infiltration behaviour was more like that of non-sodic self-mulching grey or brown clays, and raises questions regarding the amount of deep percolation when rice is grown on such soils.