Showing papers on "Soil organic matter published in 1984"
Book•
14 May 1984
TL;DR: In this article, the Mechanistic Uptake Model was used to model the Nutrient UPTake by Plant Roots Growing in Soil and the interaction of plant roots with the soil and environment.
Abstract: Chemistry of Soil-Nutrient Associations. Nutrient Absorption by Plant Roots. Nutrient Uptake by Plant Roots Growing in Soil. Modeling Nutrient Uptake by Plant Roots Growing in Soil. Interaction of Plant Roots with the Soil and Environment. Rhizosphere Microorganisms, Mycorrhizae, and Root Hairs. Nitrogen. Phosphorus. Potassium. Calcium. Magnesium. Sulfur. Boron. Copper. Iron. Manganese. Molybdenum. Zinc. Water. Application of the Mechanistic Uptake Model. Index.
1,637 citations
TL;DR: In this paper, two categories of aggregates macro- (> 250 μm) and micro- (< 250μm) depend on organic matter for stability against disruptive forces caused by rapid wetting.
Abstract: The stability of pores and particles is essential for optimum growth of plants. Two categories of aggregates macro- (> 250 μm) and micro- (< 250 μm) depend on organic matter for stability against disruptive forces caused by rapid wetting. Dispersion of clay particles from microaggregates is promoted by adsorption of complexing organic acids which increase the negative charge on clays. The acids are produced by plants, bacteria and fungi. However, the dispersibility of clay in microaggregates is offset by the binding action of polysaccharides, mainly mucilages produced by bacteria, but also by plant roots and fungal hyphae. The stability of microaggregates is also enhanced by multivalent cations which act as bridges between organic colloids and clays. Macroaggregates are enmeshed by plant roots, both living and decomposing, and are thus sensitive to management, and increase in number when grasses are grown and the soil is not disturbed. Lack of root growth, i.e. fallow, has the opposite effect. Various implications for management of soil structure are discussed.
1,556 citations
TL;DR: In a maple-beech forest in eastern New York, equal numbers of mounds, pits, and adjacent undisturbed soil microsites were censused for plant species density and cover over the growing seasons of 1978 and 1979, microrelief created a mosaic of soil properties and a vegetation pattern in the understory, both of which were affected by the presence of hemlock in the canopy.
Abstract: In a maple-beech forest in eastern New York, equal numbers of mounds, pits, and adjacent undisturbed soil microsites were censused for plant species density and cover over the growing seasons of 1978 and 1979. Several soil properties were also measured for each microsite. Detrended correspondence analysis (DCA) and chi-square goodness-of-fit tests were used to test whether the species were uniformly distributed over the microrelief positions. Comparisons of species composition, diversity, and vegetative phenologies were made between microsites and between hemlock- and hard- wood-dominated forest areas. Differences in soil properties between microsites and between the two forest areas were assessed with one-tailed paired t tests and Wilcoxon rank-sum tests, respectively. Microrelief created a mosaic of soil properties and a vegetation pattern in the understory, both of which were affected by the presence of hemlock in the canopy. Ordinations (DCA) indicated two factors that affected species composition of the microsites: (1) presence of hemlock (Tsuga canadensis) as the nearest canopy tree, and (2) microtopography (whether the microsite was a mound, pit, or undisturbed-soil site). Species in non-hemlock areas had patchy distributions in the forest community: eight species grew mainly on mounds, six in pits, and five on undisturbed soil. The mounds and pits had characteristic assemblages of species. Species richness and total density and cover of plants in each microsite were constant over the growing season. In contrast, little spatial or temporal community pattern was apparent in forest areas influenced by hemlock. The effect of hemlock on species distributions was due in part to its effect on soil properties. For all microsites, forest areas with hemlock had greater soil organic matter content, available nitrogen, cation exchange capacity, and litter depth, lower soil calcium content, moisture content, temperature, pH, and A, horizon depth; and no frost heaving. Microrelief also affected soil properties significantly. In comparison with pits, mounds were drier and poorer in nutrient content, and had a lower cation exchange capacity, less organic matter, less litter cover, a thinner A, horizon, and less snow accumulation. In areas without hemlock, the mounds were also more acid, warmer in summer and colder in winter, and more subject to frost heaving than pits. Hemlock-influenced areas had no consistent microsite differences in pH or temperature. The different microenvironments, created by the interaction of microrelief and hemlock, resulted in patchy distributions of most understory species. This pattern was likely a result of species require- ments for and tolerances of environmental conditions, tempered by competitive interactions.
529 citations
TL;DR: In this article, the stability of aggregates from 26 soils selected from agricultural areas was measured by wet-sieving and the results correlated with sand, silt, clay, nitrogen, organic matter and iron contents and with cation exchange capacity.
Abstract: SUMMARY
The stability of aggregates from 26 soils selected from agricultural areas was measured by wet-sieving and the results correlated with sand, silt, clay, nitrogen, organic matter and iron contents and with cation exchange capacity. Highly significant correlations were obtained for the relationships between aggregate stability and organic matter and some properties associated with it. No other soil constituent investigated had a significant relationship with aggregate stability, indicating that organic matter is mainly responsible for the stabilization of aggregates in these soils.
The relationships between aggregate stability, and organic matter content plus some of its component fractions were examined in more detail using 120 soils. Total organic matter, total carbohydrate and humic material extracted by various reagents each gave highly or very highly significant correlations with aggregate stability. However, whilst it was not possible to distinguish whether any one organic component was more important than another, the results indicate that soil organic matter levels can be used diagnostically to identify soils which may show problems of structural instability.
426 citations
TL;DR: In this article, a simple ashing procedure for routine determination of soil organic matter is described, and the proposed procedure incorporates a computerized weighing system and permits 1600 organic matter determinations per day.
Abstract: A simple ashing procedure for routine determination of soil organic matter is described. Two hundred fifteen soils from 19 states and Canada were ashed at 500° C and the percent weight loss plotted against the percent organic matter determined by Walkley‐Black titration. The resulting regression equation gave a correlation coefficient of 0.98. The organic matter content of experimental samples ranged from 0.64% to 52.4% as determined by the Walkley‐Black method. The proposed procedure incorporates a computerized weighing system and permits 1600 organic matter determinations per day.
336 citations
TL;DR: In this paper, the authors separated fine surface soil ( < 2 mm) into a light and a heavy fraction, and found that the light fraction had a consistently wider C:N ratio than the heavy, and net N mineralization during anaerobic incubation was greater from the heavy than from the light in five of six soils for which both fractions were incubated.
Abstract: Fine surface soil ( < 2 mm) from four sites in Oregon and Washington and three in Costa Rica was separated by repeated notation in NaI solution (sp. gr. < 1.2, 1.4, or 1.6 g cm−3) into a light and a heavy fraction. Most organic matter in the light fractions consisted of partly-decomposed root fragments and other plant and microbial remnants and most in the heavy fractions was adsorbed or deposited on mineral surfaces or was protected within organo-mineral microaggregates. The light fraction had a consistently wider C:N ratio than the heavy, and net N mineralization during anaerobic incubation was greater from the heavy than from the light fraction in five of six soils for which both fractions were incubated. Net N mineralization was greater from the heavy fraction than from the whole soil of most sites perhaps because the light fraction immobilized N released from the heavy fraction when they were incubated together. Correlation between net N mineralization (as a proportion of total N) and C:N ratio was negative for the light fraction (r2=0.74) but positive for the heavy fraction (r2 = 0.85), suggesting that the C:N ratio does not control the extent to which heavy-fraction N is mineralizable.
293 citations
TL;DR: In this article, a knowledge of the size and turnover rates of plant constituents such as cellulose and hemicellulose, and lignin is used to predict the effects of C availability on transformations of C and N.
Abstract: Dynamics of C, N, S, and to some extent P are expressed by a knowledge of the size and turnover rates of plant constituents such as soluble C and N components, cellulose and hemicellulose, and lignin. Soil organic matter constituents include: the microbial biomass as determined chemically or microscopically, non-biomass active components determined by isotopic dilution, stabilized N constituents for which good techniques are not yet available, and resistant or old C and associated N determined by carbon dating. The processes involved in the nutrient transformations and transfers are reasonably well understood. The control mechanisms require further elucidation to be able to extrapolate from the laboratory to the field, and between field sites. Major control mechanisms requiring further insight include the effects of C availability on transformations of C and N. The other control for which every little is known is that of spatial compartmentalization. Compartmentalization ranges from landscape or management sequences to pedogenic layers, rhizosphere-mycorrhizal effects, clay-sesquioxide surfaces, aggregation, localized enzymes, and microbial effects such as membrane boundaries. Control mechanisms for concurrent mineralization-immobilization, the stabilization of microbial products, and the relative role of the biomass as a catalyst rather than as a source-sink for nutrients, must be understood. There is potential for combining a knowledge of microbial production and turnover with that of the roles of the soil organic active fraction as a temporary storehouse for nutrients. This, in conjunction with management techniques such as zero tillage and crop rotation, should make it possible to better utilize soil and fertilizer N, especially in areas of the world where the cost of nutrients is high relative to the value of the crop grown.
268 citations
Abstract: Soil compaction caused by animal treading in grazing of pastures has not been considered a serious problem in Australian soils. However, recent circumstantial evidence suggests that in northern Victoria compaction does occur. In an experiment conducted at the Hamilton Pastoral Research Station (western Victoria) in 1973, grazed pastures with various stocking rates showed increases in bulk density and bearing capacity of the soil, and decreases in hydraulic conductivity occurred with increasing stocking rate. Some change in pasture composition was also noted.
206 citations
TL;DR: In previous simple models describing decomposition of organic matter, the rate of decomposition was usually assumed to be constant as mentioned in this paper, but this was not true and experimental evidence has shown this is not true.
Abstract: In previous simple models describing decomposition of organic matter, the rate of decomposition was usually assumed to be constant. Experimental evidence has shown this is not true. The objective of this study was therefore to find a relationship between decomposition rate and time. This resulted in an equation (Eqn 5), that can be used for many types of organic materials, provided their ‘apparent initial age’ is known. This age is related to the humification coefficient and varies from 1 year for green matter to 14 years for some peats. Formulas to calculate accumulation and decomposition of ‘young’ soil organic matter were also derived.
192 citations
TL;DR: In this paper, a new P fractionation scheme was proposed for soil microorganisms with estimates of Pi and Po fractions that vary in the extent of their availability to plants, which enabled the dynamics of short-term soil P transformations to be investigated in relation to long-term changes observed in the field.
Abstract: Organic forms of soil phosphorus (Po) are an important source of available P for plants following mineralisation. The rates and pathways of P through soil organic matter are, however, poorly understood when compared to physico-chemical aspects of the P cycle. The essential role of soil microorganisms as a labile reservoir of P, confirmed experimentally and in modelling studies, has recently led to the development of methods for measuring their P content. Incorporation in a new P fractionation scheme of these measurements with estimates of Pi and Po fractions that vary in the extent of their availability to plants has enabled the dynamics of short-term soil P transformations to be investigated in relation to long-term changes observed in the field.
150 citations
Book•
31 Mar 1984
TL;DR: In this article, the authors discuss the benefits of using no-tillage and the disadvantages of using it in agriculture, and present a philosophy in No-Tillage.
Abstract: 1. Introduction.- Reasons for Tillage.- Factors that Contributed to the Increased Interest in No-Tillage Systems.- Advantages of No-Tillage.- Disadvantages of No-Tillage.- Present Philosophy in No-Tillage.- 2. Effects of Climate on Performance of No-Tillage.- Precipitation and Evapotranspiration.- Soil Temperature.- Corn Seedling Growth as Related to Soil Temperature.- Time of Planting.- 3. Soil Adaptability for No-Tillage.- Some Factors Affecting Adoption of No-Tillage 42 Soil Drainage.- Suitability for Sloping Land.- Soil Water Erosion.- Erosion Control by No-Tillage.- Controlling Soil Wind Erosion by No-Tillage.- Steeplands.- 4. Soil Moisture.- Effect of Mulch on Evaporation of Soil Water.- Effect of Soil Texture, Pans and Drainage Class on Soil Water Evaporation.- Soil Water in Field Studies.- Effect of No-Tillage on Root Growth.- 5. Fertilization and Liming.- The Soil Environment Under No-Tillage Versus Conventional Tillage.- Nitrogen Requirements for No-Tillage Crops.- Pathways of Nitrogen in the Two Systems.- Methods of Nitrogen Application.- Phosphorus Requirements.- Potassium Distribution and Availability in the Soil.- Soil Acidity and Lime.- Sulfur.- Micro nutrients.- Role of Cover Crops in Nitrogen Fertilization of No-Tillage.- 6. Energy Requirement in No-Tillage.- Energy Use in Agriculture.- Need for Energy Conservation in Agriculture.- Energy Use and Efficiency in Tillage Systems.- Tillage Operations.- Planting.- Field Machinery.- Seeding Rates.- Weed Control.- Comparison of Tillage System.- Energy Efficiency in Fertilizer Management.- Tillage and Nitrogen Fertilizer Efficiency.- Time of Application and Nitrogen Fertilizer Efficiency.- Effect of Fertilizer Placement on Efficiency.- Nitrogen from Legume Cover Crops.- Energy Efficiency in Forage Production.- 7. Response of Weeds and Herbicides Under No-Tillage Conditions.- Some Factors Affecting Weed Control in No-Tillage.- Effect of Surface Plant Residue on Herbicide Persistence.- 8. Other Pests in No-Tillage and Their Control.- Insects.- Soil Insects.- Above-Ground Insects.- Diseases.- Corn.- Sorghum.- Soybeans.- Wheat.- Summary.- 9. Changes in Soil Properties Under No-Tillage.- The Microbial Environment.- Number and Activity of Soil Microorganisms.- Tillage Effects on Soil Animals.- Decomposition of Organic Matter.- Mineralization and Immobilization of Nitrogen.- Effects of Tillage on Nitrification and Denitrification.- Soil Physical Properties.- Influence of Mulches on Soil Physical Properties.- Effect of Tillage on Soil Density and Porosity.- Chemical Properties.- Phosphorus and Potassium.- Magnesium.- Summary of Chemical Properties.- 10. Multicropping.- Multicropping With No-Tillage Techniques.- Beginnings of Multiple Cropping in the United States.- Requirements for Successful Multiple Cropping.- Length of Growing Season.- Water.- Weed Control.- Fertilizer Practices.- Equipment.- Management of Multiple Cropping.- Profitability of Multiple Cropping.- The Future of Multiple Cropping.- Winter-Summer Double Cropping.- Summer-Summer Double Cropping.- Winter-Summer-Summer Double Cropping.- Other Multiple Cropping Systems.- External Factors Affecting Profitability of Multiple Cropping.- Combining Agronomic Practices for Multicropping on Sloping Land.- 11. Equipment.- Planters and Planting No-Tillage.- Types of Planters.- Tractor Requirements for No-Tillage.- Pesticide Applicators.- Hand Planting.- 12. No-Tillage in the Tropics.- Soil Resources.- Distribution and Classification of Tropical Soils.- Properties and Characteristics of Tropical Soils.- Soil Fertility.- Erosion Problems.- Water Resources.- Climatic Conditions in the Tropics.- Soil Moisture Storage and Water Use.- Conservation of Water Using No-Tillage.- Human Resources.- Availability of Labor.- Other Sources of Energy.- Acceptance of New Technology.- Management Ability.- Prospects for Success of No-Tillage in the Tropics.- Small Farmers and Large-Scale Farmers.- Soil Conservation.
TL;DR: The study confirmed that the microbially mediated processes of mineralization and humification remove sludge hydrocarbons from soils of landfarms with reasonable efficiency.
Abstract: A 1,280-day laboratory simulation of the "landfarming" process explored the fate in soil of polynuclear aromatics (PNAs) and total extractable hydrocarbon residues originating from the disposal of an oily sludge. In addition to the measurement of CO(2) evolution, periodic analyses of PNAs and hydrocarbons monitored biodegradation activity. The estimation of carbon balance and of soil organic matter assessed the fate of residual hydrocarbons. Seven sludge applications during a 920-day active disposal period were followed by a 360-day inactive "closure" period with no further sludge applications. A burst of CO(2) evolution followed each sludge addition, but substantial amounts of undegraded hydrocarbons remained at the end of the study. Hydrocarbon accumulation did not inhibit biodegradation performance. Conversion of hydrocarbons to CO(2) predominated during active disposal; incorporation into soil organic matter predominated during the closure period. In this sludge, the predominant PNAs were degraded more completely (85%) than total hydrocarbons. Both biodegradation and abiotic losses of three- and four-ring PNAs contributed to this result. Some PNAs with five and six rings were more persistent, but these constituted only a small portion of the PNAs in the sludge. The study confirmed that the microbially mediated processes of mineralization and humification remove sludge hydrocarbons from soils of landfarms with reasonable efficiency.
TL;DR: Sulphur in agricultural soils occurs in organic and inorganic forms, with organic S accounting for > 95% of the total S in the United States and Canada as discussed by the authors.
Abstract: Sulphur in agricultural soils occurs in organic and inorganic forms, with organic S accounting for > 95% of the total S. Analysis of a wide range of soils shows that from 25 to 75% of the organic S in soils is HI-reducible, from 7 to 30% is C-bonded, and from 11 to 22% is unidentified S. Nitrogen is associated with S in soil organic matter in a ratio of about 8 : 1, although the extreme ratios may vary from 5: 1 to 13: 1. Laboratory studies showed that humus S is depleted faster than humus N. Mineralization of S in crop residues varied with type of crop residue and soil studied The amounts of S fertilizers (gypsum, elemental S, and sulfuric acid) used in the United States in 1981 and 1982 were 1.9 × 106 and 1.5 × 106 tons, respectively. Of the total amount used in 1982, 3, 5, 20, and 71% were used in the West North Central, Mountain, South Atlantic, and Pacific regions, respecitively. A survey of S deposition at about 100 sites in the United States and many other sites in Canada in 1980 showed that annual addition by precipitation in North America ranged from 0.5 to slightly above 10 kg/ha. The usual ranges of values in concentrations and spatial rates of N, P, and S in precipitation is well within the ranges of these elements in natural waters. Atmospheric sources are important components in meeting crops S requirements and should be considered in benefit-cost analyses relating to S emissions.
01 Jan 1984
TL;DR: In this article, the authors show that the microbial activity of a soil is largely determined by the chemical and physical properties of the soil, and that the placement and amount of organic material directly influences biological activity.
Abstract: When farmers shift from a system of agricultural production that includes numerous tillage operations to a reduced or no-tillage system it is reasonable to show concern about how this change in soil management may affect soil properties. For any crop production system to be widely accepted and used it must maintain the physical properties of the soil, and allow for replacement of nutrient removal and other losses. It must also maintain a soil environment favorable for the numerous necessary biological reactions. The microbial activity of the soil is largely determined by the chemical and physical properties of the soil. For example, the placement and amount of organic material directly influences biological activity, as it also does the chemical and physical properties.
TL;DR: Much of the tritium found in soil and leaf litter near a chemical separations facility is incorporated into soil organic matter in a stable non-exchangeable form, which seems to result from the uptake of moleculartritium by living pine needles.
Abstract: Much of the tritium found in soil and leaf litter near a chemical separations facility is incorporated into soil organic matter in a stable non-exchangeable form. Formation of this ''bound'' tritium seems to result from the uptake of molecular tritium (HT) by living pine needles. Soil and litter microbes convert HT to HTO more rapidly, but no measurable organic tritium is formed. This report discusses this study.
TL;DR: In this article, the authors examined the variability in the natural enrichment of 15N in total nitrogen (N) and several N fractions for profiles of pasture soils differing in parent material and period under Trifolium subterraneum.
Abstract: Variability in the natural enrichment of 15N in total nitrogen (N) and several N fractions was examined for profiles of pasture soils differing in parent material and period under Trifolium subterraneum. The natural enrichment of 15N in the total N of surface soils (0-5 cm) within a 400 km2 catchment ranged from 2.55 to 6.79?(expressed as a15N with respect to atmospheric N2). There was no relationship with parent material, period under T. subterraneum or concentration of total N in the soil. In one soil, lateral variations in a15N over a 12 m2 grid were within the range of 5.01 to 7.95?. The a15N of total soil N always increased with depth in the soil profiles. This was associated with an increase in the stable clay-sized humus fraction, which had a higher a15N than the less humified organic N in sand and silt-sized fractions. One soil was separated into four depth layers in which a15N in the inorganic N, mineralizable N, plant-extractable N and total soil N were determined. The first three parameters all had lower a15N values than the total soil N. The a15N of total N increased with soil depth, whereas there was no change with depth in the other three parameters.
TL;DR: The natural N isotope composition of soil organic matter associated with organo-mineral particle size fractions of two cultivated and two native grassland soils was studied in this article, where the authors attributed the increase in the abundance of fine-silt and coarse-clay-associated N to reduced inputs of plant residues under cultivation.
Abstract: The natural N isotope composition of soil organic matter associated with organo-mineral particle size fractions of two cultivated and two native grassland soils was studied. In the native soils, N associated with the coarsest (sand size) fraction showed a low enrichment (+7 per mil ¹⁵N enrichment) typical for recent plant materials. A similarly low enrichment was observed in the silt-sized fractions (+9 δₐ ¹⁵N) whereas clays had a higher ¹⁵N abundance (>12 δₐ ¹⁵N), characteristic of residual material from microbially-mediated N mineralization. Cultivation initially resulted in the incorporation of a large pulse of low-enrichment plant material that could be detected in the sand and coarse silt fractions, as well as in the fine clays that contain a large portion of the soil's microbial products. The ¹⁵N abundance of fine-silt and coarse-clay-associated N appeared relatively unchanged even after prolonged cultivation of 60 yr. Increases in the ¹⁵N abundance of the sand and silt fractions were attributed to reduced inputs of plant residues under cultivation. A large drop in the ¹⁵N abundance of the fine-clay-sized materials indicated a major change in the nature of microbial N transformations.
TL;DR: In this paper, changes in the composition of organo-mineral particle size fractions as a result of cultivation of a grassland soil are discussed with reference to models of soil organic matter formation and turnover.
Abstract: Changes in the composition of organo-mineral particle size fractions as a result of cultivation of a grassland soil are discussed with reference to models of soil organic matter formation and turnover. The data presented indicated that physically stabilized organic matter is an important reservoir, with an intermediate turnover time, which is responsible for nutrient supply in agricultural soils. Possible mechanisms of stabilization and mobilization of organic matter are presented in the light of the arrangement of organic and inorganic components of the soil.
TL;DR: In this article, the authors investigated quantitative relationships between the microbial decomposition of soil organic matter and the oxidation-reduction reactions in the submerged soils which are affected by soil temperature.
Abstract: We have investigated quantitative relationships between the microbial decomposition of soil organic matter and the oxidation-reduction reactions in the submerged soils which are affected by soil temperature. Seven soil samples of manured and non-manured plots with varying contents of organic matter, active iron, active Mn, etc. were used either after air-drying or without air-drying. They were incubated anaerobically in truncated syringes for 12 weeks at 15, 20, 30, and 40°C, and Eh as well as the contents of Fe(II), Mn(II), volatile fatty acids (VFA), dissolved gaseous components (CO2, CH4, N2O, and O2+Ar) and sulfides were determined. Air-drying pretreatment and high incubation temperature were found to enhance the development of the reduction state in the submerged soils. Both Mn(II) and Fe(II) contents increased rapidly and reached maximum levels which did not change afterwards. These maximum values were specific for each soil and were not affected by either the incubation temperature or the air-dryin...
TL;DR: A mathematical model study has shown that lake water becomes acidic when hydrologic conditions force precipitation to flow to the lakes as surface flow or as lateral flow through the shallow organic soil horizon.
Abstract: Woods and Panther lakes in the Adirondack Mountains of New York respond differently to the same acidic deposition. A mathematical model study has shown that lake water becomes acidic when hydrologic conditions force precipitation to flow to the lakes as surface flow or as lateral flow through the shallow organic soil horizon. Hydrographic data, capacity of flow through inorganic soil horizons, runoff recession curves, and groundwater level fluctuations of Woods and Panther lake basins provide independent evidence to support the thesis that the acidic state of a lake depends on the paths the tributary water takes as it passes thorough the terrestrial system. It is concluded thot Panther Lake is more alkaline than Woods Lake, because a larger proportion of the precipitation falling on the basin passes through deeper mineral soil horizons.
TL;DR: In this article, 14C and 12N-labeled Medicago littoralis and Medicago truncatula plant parts, ground or unground, were added at a rate equivalent to 50 kg nitrogen ha-l to a calcareous soil in the field and allowed to decompose for two years.
Abstract: 14C- and 12N-labelled Medicago littoralis and Medicago truncatula plant parts, ground or unground, were added at a rate equivalent to 50 kg nitrogen ha-l to a calcareous soil in the field and allowed to decompose for two years. Both plant types behaved similarly but the various plant parts decomposed to different extents. After 4 weeks' and 2 years' decomposition respectively, the residual organic 14C in soil from leaves of both Medicago species accounted for about 62% and 20% of input, from stems 70% and 24% and from roots 80% and 32%. Average residual organic 15N accounted for 64% and 40% of leaf 15N, 87% and 56% of stem and 81% and 50% of root 15N. Grinding had no effect on the residual 14C and 15N of plant parts. After 2 years' decomposition the proportion of residual and 15N present as labelled biomass was greatest for leaf residues. Results from laboratory studies of 20 weeks' decomposition of ground and unground Medicago littoralis plant parts under continuously moist and intermittently dry and rewetting conditions were consistent with field results. Grinding significantly promoted pod decomposition under most incubation conditions. Drying and rewetting promoted decomposition of the plant parts. Pods were affected more than other parts. The longer the time moist following drying, the greater the decomposition. The more frequent the drying and wetting cycles, the greater the decomposition.
TL;DR: In this paper, the procedure for estimating net nitrogen mineralization proposed by Stanford and co-workers was used to determine Arrhenius relationships between the rate constants (k) and absolute temperature (°K) for 33 virgin and cultivated Western Canadian prairie surface (0-15 cm) soils.
Abstract: There is a need to provide quantitative relationships that will allow agronomists to estimate accurately the nitrogen-supplying power of soils while taking into account both temperature and soil moisture variations. The procedure for estimating net nitrogen mineralization proposed by Stanford and co-workers was used to determine Arrhenius relationships between the rate constants (k) and absolute temperature (°K) for 33 virgin and cultivated Western Canadian prairie surface (0–15 cm) soils. There was no significant difference in Arrhenius relationship between soils within each soil zone; thus, a single average Arrhenius equation was calculated per soil zone. Average Q10 for the Brown chernozemic soils was 2.75, for the Dark Brown, thin Black and thick Black chernozems, 2.18, and for the Gray luvisols, 2.0. These Q10 values are as high or higher than those reported in other parts of the world and may be related to the degree of degradation of the soil organic matter in these various soils. Culture had no ma...
TL;DR: In this article, the authors developed from mixed and multiple-cropping systems with relatively closed N cycles to intensively managed monocultures with large N inputs in the form of commercial fertilizers.
Abstract: Agro-ecosystems have developed from mixed- and multiple-cropping systems with relatively closed N cycles to intensively managed monocultures with large N inputs in the form of commercial fertilizers. Cultivation of increasingly larger areas of land has resulted in substantial losses of soil organic matter and N. Also, the move from slash and burn agriculture to intensively ploughed systems has resulted in losses through increased erosion.
TL;DR: The decreasing trends with soil formation in the ratios of mineral to organic nitrogen and of nitrate to ammonium nitrogen could be accounted for by the higher activity of immobilization by microorganisms and uptake by plants in the more mature ecosystem.
Abstract: The spatial pattern of soil nitrogen was analyzed for a patchy vegetation formed by the colonization of Polygonum cuspidatum in a volcanic “desert” on Mt. Fuji. Soils were sampled radially from the bare ground to the center of the patch, and analyses were done for bulk density, water content, soil acidity, organic matter, organic nitrogen, and ammonium and nitrate nitrogen. The soils matured with succession from the bare ground through P. cuspidatum to Miscanthus oligostachyus and Aster ageratoides sites: bulk density decreased, and water content, organic matter, organic nitrogen, and ammonium nitrogen increased. Nitrate nitrogen showed the highest values at the P. cuspidatum site. Application of principal component analysis to the soil data discriminated two component factors which control the variation of soil characteristics: the first factor is related to soil formation and the second factor to nitrogen mineralization and nitrification. The effect of soil formation on nitrogen mineralization and nitrification was analyzed with a first-order kinetic model. The decreasing trends with soil formation in the ratios of mineral to organic nitrogen and of nitrate to ammonium nitrogen could be accounted for by the higher activity of immobilization by microorganisms and uptake by plants in the more mature ecosystem.
TL;DR: An inherent biomass is characteristic of a soil while the input of substrates for plant roots or crop residues promotes the transient (zymogenous) biomass, however successful micro-organisms will show aspects of both types of ecological strategy.
Abstract: An inherent (autochthonous) biomass is characteristic of a soil while the input of substrates for plant roots or crop residues promotes the transient (zymogenous) biomass. However successful micro-organisms will show aspects of both types of ecological strategy. The biomass generated from plant residue substrates can include toxin-producing and pathogenic species but also beneficial organisms such as N-fixers and polysaccharide-producers. Rhizosphere activity can, depending on soil, plant and microbial species, stabilize or destabilize soils. Microbial activity should be considered in soil management and it may be possible to manipulate the soil population balance towards beneficial organisms.
TL;DR: The effects of disturbing (cultivating) and stockpiling prairie grassland topsoil on microbial activity, microbial biomass C, plant production and decomposition potentials were studied by measuring CO2 efflux from unamended and glucose amended soil in the laboratory and by conducting a pot and litter bag study in the greenhouse as discussed by the authors.
Abstract: The effects of disturbing (cultivating) and stockpiling prairie grassland topsoil on microbial activity, microbial biomass C, plant production and decomposition potentials were studied by measuring CO2 efflux from unamended and glucose amended soil in the laboratory and by conducting a pot and litter bag study in the greenhouse. Stockpiling appeared to have very little effect on soil respiratory activity, but did reduce the microbial biomass C levels. Throughout the 3 year study the microbial biomass C in the surface soil of the stockpile was less than that in the undisturbed soil, while the biomass C in soil at the bottom of the stockpile was at no time significantly different from that in the undisturbed soil. The reduction in microbial biomass C in the surface soil immediately after stockpiling was attributed to a decrease in the soil organic C levels caused by a slight dilution of the topsoil with subsurface mineral soil, and the exposure of the stockpile surface to extreme environmental conditions. Soils from all depths of the stockpile responded more slowly to the addition of glucose than soil from the undisturbed and cultivated treatments even when no differences in biomass were detected between the undisturbed and stockpiled soils. It is postulated that the rapidity with which the soil microbial biomass responds to glucose additions may be a sensitive indicator of stress on the soil biological components. The reduction in biomass after storage for 1 year had no adverse effects on the decomposition or primary production potential of the stored soil. Rather, shoot production by fall rye was stimulated in the stored topsoil, presumably a result of better N nutrition.
TL;DR: Assessment of characteristics that could be related to soil organic matter breakdown in ungrazed and heavily grazed mixed prairie and fescue grassland ranges found total C was higher in samples from heavily grazing sites than in those from ung grazed sites and was higher over the winter months than during the summer.
Abstract: Total C, water-soluble C, and 3 soil enzymes associated with Ah horizons under ungrazed mixed prairie and fescue grassland ranges were assessed over a 23-month period. Generally, total C was higher in samples from heavily grazed sites than in those from ungrazed sites and was higher over the winter months than during the summer. Water-soluble C was generally higher in soil from mixed prairie than in soil from fescue grassland except for short periods during the winter. Enzymatic activities are highest in samples from the fescue grassland site regardless of grazing intensity. Enzymatic activities of both sites increased during the winter months. Grazing intensity affected enzymatic activities differently at the 2 sites. A working hypothesis is proposed to account for organic matter breakdown during the winter and spring months. Many soil biological processes are related to the decomposition of organic residues which in prairie soils come predominantly from plant roots. This decomposition varies with seasons. In a 3-year study of blue grama (Boutelouagracilis), over 50% of the root mass disappeared between October and May each year (Dormaar et al. 1981). Although only fragmentary information is available on year-round enzymatic soil activities, Khaziyev (1977) has shown that the annual pattern for CO2 liberation reached a maximum when the soil was frozen and that the potential for enzymatic activity increased in winter and early spring but decreased in the summer. Since water-soluble C is a measure of soluble, low molecular weight organic compounds, they can act as substrates for biological processes (Ivarson and Sowden 1970). Seasonal changes in soil enzymatic activity (Kiss et al. 1975, Khaziyev 1977), and changes in the amount and condition of the substrate upon which they act, may thus be related to any seasonal changes in rates of biological processes in the soil. Generally enzymes accumulated in soil have biological significance as they participate in the cycling of elements and thus play a very important role in the initial phases of the decomposition of organic residues (Kiss et al. 1975). Specifically, dehydrogenase activity in soils provides correlative information on the biological activity and microbial populations; phosphatase activity is thought to be directly related to the level of organic phosphorus in the soil; urease activity generally correlates with organic matter content due to its existence as a complex with organic constituents (Skujins 1973, 1976). The purpose of this study was to assess over a 2-year period several characteristics that could be related to soil organic matter breakdown in ungrazed and heavily grazed mixed prair
TL;DR: The model of Uehara and Gillman was used to estimate the amounts of permanent surface charge and variable surface charge at soil pH, in two soils from the high rainfall region of coastal Queensland as discussed by the authors.
Abstract: The model of Uehara and Gillman was used to estimate the amounts of permanent surface charge, and variable surface charge at soil pH, in two soils from the high rainfall region of coastal Queensland. For each soil series, samples from virgin rain-forest were compared with soil collected from nearby sugarcane fields. One soil contained relatively large amounts of permanent negative charge (up to 3 m.e. per 100g), and hence was moderately supplied with exchangeable cations, while the other soil was dominated by variable charge components and at soil pH contained sufficient positive charge to reduce exchangeable cations to near zero values, despite the presence of about 1 m.e. per 100 g of permanent negative charge. In the latter the position of soil pH with respect to the point of zero charge is of utmost importance for the development of cation exchange capacity. The effect of adsorbed sulfate on positive charge measurement, and valency of the ion used for negative charge measurement, are briefly discussed.
TL;DR: In this article, a nonlinear regression procedure was used with published data (Stanford and Smith for 34 soil samples to estimate the size of a pool (N1) which mineralized within four weeks, and the pool size and first order mineralization rate constant (k2).
Abstract: Recent simulation models of soil organic matter and N transformations postulate several pools of soil N with differing stabilities. A nonlinear regression procedure was used with published data (Stanford and Smith for 34 soil samples to estimate the size of a pool (N1) which mineralized within four weeks, and the pool size (N1) and first order mineralization rate constant (k2) of a pool which mineralizes more slowly and which is similar to the “active”; N fraction described by Parton et al. Regression equations including all 34 samples based on total soil nitrogen, organic carbon, pH, and dummy variables for soil order, temperature and moisture regimes, texture, and presence of free calcium carbonate accounted for 55%, 86%, and 53% of the variation in N1, N2, and k2, respectively. Several simulation models of soil organic matter transformations have been developed recently (Parton et al.4, Jenkinson and Rayner5, Paul and Van Veen6. These models assume that soil organic matter exists in pools diff...