Showing papers on "Soil organic matter published in 1991"

Model estimates of CO2 emissions from soil in response to global warming

Abstract: ONE effect of global warming will be to accelerate the decomposition of soil organic matter, thereby releasing CO2 to the atmosphere, which will further enhance the warming trend1–7. Such a feedback mechanism could be quantitatively important, because CO2 is thought to be responsible for ∼55% of the increase in radiative forcing arising from anthropogenic emissions of gases to the atmosphere8, and there is about twice as much carbon in the top metre of soil as in the atmosphere9. Here we use the Rothamsted model for the turnover of organic matter in soil3 to calculate the amount of CO2 that would be released from the world stock of soil organic matter if temperatures increase as predicted, the annual return of plant debris to the soil being held constant. If world temperatures rise by 0.03 °C yr−1 (the increase considered as most likely by the Intergovernmental Panel on Climate Change8), we estimate that the additional release of CO2 from soil organic matter over the next 60 years will be 61 × 1015 gC. This is ∼19% of the CO2 that will be released by combustion of fossil fuel during the next 60 years if present use of fuel continues unabated.

Effects of temperature and substrate quality on element mineralization in six arctic soils

Abstract: We compared the effects of temperature on rates of microbial respiration, N mineralization, nitrification, and P mineralization in soils from six arctic ecosystems located along a toposequence on Alaska's North Slope. Soils from these ecosystems were incubated aerobically in the laboratory for 13 wk and at temperatures representative of field values during a typical growing season. Rates of C and N mineralization were insen- sitive to temperature between 30 and 90C but increased by factors of 2 or more between 90 and 15?. For both C and N, differences in mineralization rates among soils were greater than differences due to incubation temperature within single soils. This suggests that the quality of soil organic matter varies widely among these ecosystems and is more important than soil temperature differences in controlling rates of these processes in the field. Nitri- fication occurred in all soils, even at 30, but there were large differences among soils in nitrification potentials. Overall differences in P mineralization between soils were small. Rates of P mineralization, however, decreased with increasing temperature in soils from some sites and increased with temperature in others. Carbon respired during the 1 3-wk incubations ranged between 1.5 and 8% of total soil organic C across soil types and incubation temperatures. In contrast to the relatively high C mineralization rates in these soils, net N and P mineralization rates were very low and were likely due to high microbial demands for these nutrients. High microbial demand for mineral nutrients can severely limit plant N and P availability in arctic soils.

The behavior of mercury in the soil with special emphasis on complexation and adsorption processes - A review of the literature

Abstract: The behavior of Hg in the soil is mainly controlled by adsorption and desorption processes depending on complexation, the most important ligands in solution being OH−, Cl−, and organic anions. Since the solubility of HgCl2 and Hg(OH)2 is rather high, the affinity of Hg to these ligands leads to an increased mobility. This is especially true for HgCl2, whereas the hydrolysis of Hg2+ may result in the specific adsorption of Hg on mineral colloids. The high affinity of Hg to S explains the strong binding of Hg to soil organic matter and also the stability of HgS. Further precipitation products than HgS are unlikely to occur, since the activity of Hg2+ remains too low to exceed the solubility product of any other defined Hg compound. It is mainly the physical fractioning of soil organic matter (dissolved vs adsorbed) that determines the behavior and distribution of Hg in soils.

Soil fauna and soil structure

Abstract: Significant effects of soil fauna on soil structure are achieved mainly by a few groups among the larger soil invertebrates that are widely distributed and generally present in large numbers. Of these groups the most important are earthworms, termites and ants. The review deals mainly with earthworms, which are distributed throughout all but the coldest and the driest regions of the world. The effects of termites and ants on soil structure are also discussed. These groups of soil animals are also widely distributed, but are most common and most effective in influencing soil structure in tropical and warm temperate regions. A brief section deals with the influence of microarthropods, which are commonly found in large numbers, but because of their small size are unable to make large burrows in the mineral soil horizons, and are largely confined to pre-existing voids in litter and surface soil horizons. Their faecal pellets are granular and largely organic, with little included mineral soil material, and they sometimes make up the major proportion of forest litter layers. Quantitative assessment of the influence of earthworms on soil structure is available, but information on other groups is largely qualitative. The burrows of earthworms contribute to macroporosity and so influence water infiltration and aeration. Anecic species, that live in semi-permanent burrows opening to the soil surface and feed at the surface, provide more or less vertical channels for water infiltration and gas exchange. Endogeic species, that burrow continuously in search of food within the soil, provide more horizontally oriented, frequently extensive and intersecting networks of macropores that promote water movement and gas diffusion. Burrows that penetrate soil surface crusts are particularly important for water entry to the soil. Water movement through pores of the dimensions of earthworm burrows is important only when rainfall or irrigation supplies water at rates that exceed the capacity of the soil surface for capillary uptake. The combination of increase in surface area available for capillary uptake through the burrow walls and of hydraulic pressure resulting from the column of water in a water-filled burrow increases infiltration. Occupied burrows of anecic species may be sealed with soil or plant litter by the resident earthworm when water is ponded on the soil surface, or blocked by the earthworm's body, so as to be ineffective for water infiltration. When burrows are air-filled they provide surfaces that penetrate below ground and facilitate gas exchange.

Simulation of nitrogen dynamics and biomass production in winter wheat using the Danish simulation model DAISY

Abstract: A dynamic simulation model for the soil plant system is described. The model includes a number of main modules, viz., a hydrological model including a submodel for soil water dynamics, a soil temperature model, a soil nitrogen model including a submodel for soil organic matter dynamics, and a crop model including a submodel for nitrogen uptake. The soil part of the model has a one-dimensional vertical structure. The soil profile is divided into layers on the basis of physical and chemical soil characteristics. The simulation model was used to simulate soil nitrogen dynamics and biomass production in winter wheat grown at two locations at various levels of nitrogen fertilization. The simulated results were compared to experimental data including concentration of inorganic nitrogen in soil, crop yield, and nitrogen accumulated in the aboveground part of the crop. Based on this validation it is concluded that the overall performance of the model is satisfactory although some minor adjustments of the model may prove to be necessary.

Sodicity and soil structure

Abstract: Sodic soils are widespread in Australia reflecting the predominance of sodium chloride in groundwaters and soil solutions. Sodic soils are subject to severe structural degradation and restrict plant performance through poor soil-water and soil-air relations. Sodicity is shown to be a latent problem in saline-sodic soils where deleterious effects are evident only after leaching profiles free of salts. A classification of sodic soils based on sodium adsorption ratio, pH and electrolyte conductivity is outlined. Current understanding of the processes and the component mechanisms of sodic soil behaviour are integrated to form the necessary bases for practical solutions in the long term and to define areas for research. The principles of organic and biological amelioration of sodicity, as alternatives to costly inorganic amendments, are discussed.

Soil organic matter: the next 75 years

Abstract: Part I of this paper presents an account of what we know at this time about SOM (soil organic matter). It deals with the distribution and functions in soils of SOM, descriptions of methods of extraction and fractionation, and chemistry of the major components. These include carbohydrates, nitrogenou

Long-Term Impacts Of Tillage, Fertilizer, And Crop Residue On Soil Organic Matter In Temperate Semiarid Regions

Abstract: Publisher Summary This chapter reviews past progress toward enhancing the level and quality of organic matter in soil. Annual cropping replaced fallow in many areas, which has reduced organic matter loss from soil. Greater fertilizer use and varietal improvement increased cereal grain yield and straw production, which raised the level of C return to the soil. Carbon input has shown to have a significant impact on the organic matter level. Stubble-mulch and no-till systems conserved up to 2% more organic matter per year in surface soil than plowing. Crop rotation, green manuring, and reduced tillage practices have lost some of their glamour with the advent of chemical fertilizers and pesticides, and many of the long-term experiments have been discarded for more pressing research. Fertilizer and tillage research has expanded, and crop improvement has received new impetus. Less reliance on crop rotation and green manure has beenpartially responsible for increasing use of inorganic fertilizer. Soil erosion tends to increase with less crop rotation and greater reliance on mechanical tillage and clean fallow.

The effects of climate change on decomposition processes in grassland and coniferous forests

Abstract: Current models of climate change predict a reduction of area covered by northern coniferous forests and tundra, and an increase in grasslands. These scenarios also indicate a northerly shift in agricultural regions, bringing virgin soils under cultivation. The direct effects of man on tundra, boreal forest, and temperate grassland ecosystems are likely to result in less carbon mobilization from soils and vegetation than from tropical forests. However, as a consequence of climate change, carbon mineralization rates from arctic and sub-arctic soils could be very rapid under warmer and drier conditions because of low stabilization of soil organic matter (SOM) and enhanced microbial responses to small changes in soil moisture and temperature. Predicting the response of these systems to climate change is complicated where the edaphic environment regulating SOM dynamics is not a direct function of macroclimatic conditions. Grasslands contain a greater proportion of highly stabilized SOM than coniferous forests, distributed over greater depth in the soil profile, which is less susceptible to changes in mineralization rates. It is concluded that short-term responses of soil processes to climate change are more predictable in well-drained grassland and forest soils than in waterlogged soils of the tundra and boreal region. Over longer periods of time, however, plant species and soil types will alter in response to new temperature and moisture regimes above- and belowground interacting with the effects of carbon enrichment and changes in nutrient availability. The dynamics of these plant-soil interactions and the future status of soils in different life zones as sources or sinks of carbon is poorly understood. More data are also needed on the distribution of waterlogged forest soils in the boreal zone and responses to warming, which include the production of methane as well as CO2 . The primary recommendation for future research is for integrated studies on plant and soil processes.

A general biogeochemical model describing the responses of the C and N cycles in terrestrial ecosystems to changes in CO2, climate, and N deposition

Abstract: A model that simulates carbon (C) and nitrogen (N) cycles in terrestrial ecosystems is developed. The model is based on the principle that the responses of terrestrial ecosystems to changes in CO(2), climate, and N deposition will encompass enzymatic responses, shifts in tissue stoichiometry, changes in biomass allocation among plant tissues, altered rates of soil organic matter turnover and N mineralization, and ultimately a redistribution of C and N between vegetation and soils. The model is a highly aggregated, process-based, biogeochemical model designed to examine changes in the fluxes and allocation of C and N among foliage, fine roots, stems, and soils in response to changes in atmospheric CO(2) concentration, temperature, soil water, irradiance, and inorganic nitrogen inputs. We use the model to explore how changes in CO(2) concentration, temperature, and N inputs affect carbon storage in two ecosystems: arctic tundra and temperate hardwood forest. The qualitative responses of the two ecosystems were similar. Quantitative differences are attributed to the initial distribution of C and N between vegetation and soils, to the amounts of woody tissue in the two ecosystems, and to their relative degree of N limitation. We conclude with a critical analysis of the model's strengths and weaknesses, and discuss possible future directions.

Soil structure and plant growth

Abstract: Soil structure affects plant growth in many ways. Roots grow most rapidly in very friable soil, but their uptake of water and nutrients may be limited by inadequate contact with the solid and liquid phases of the soil. This contact is much more intimate in hard soil, but then the growth of the roots is strongly inhibited, so that their foraging ability is poor, and the plant may eventually become short of water or nutrients. However, many soils, even if hard, contain continuous macropores that provide niches for the roots to grow in. The presence of such macropores increases the extent of the root system, but because the roots are clumped within them, the rate at which the roots can extract water and nutrients from the soil between the macropores is considerably slowed. These macropores also provide niches for microorganisms, both symbiotic and pathogenic, so that the response of roots to different tillage treatments may differ markedly on this account alone. Soil structure not only affects the ability of roots to grow and to supply the leaves with water and nutrients; if adverse, it also induces them to send hormonal signals that slow the growth of the shoot, even if they are currently able to take up adequate water and nutrients.

Fungal hyphae and structural stability of soil

Abstract: This review describes the possible mechanisms by which fungal hyphae, especially those of vesicular-arbuscular mycorrhizal (VA) fungi, bind microaggregates of soil ( 0.25 mm), and suggests a model of the formation of a stable macroaggregate by fungal hyphae. Factors which affect the growth of VA mycorrhizal hyphae in soil and their production of extracellular polysaccharides are discussed in relation to stable macroaggregates. The interactions between clay particles and hyphae are described. The review suggests areas of future research on stabilization of aggregates by VA mycorrhizal hyphae.

Automatic, real-time monitoring of soil moisture in a remote field area with time domain reflectometry

Abstract: A multiplexing time domain reflectoinetry (TDR) system for real-time monitoring of volumetric soil moisture content was developed. The system was tested at a remote field site in the Hubbard Brook Experimental Forest in New Hampshire. The average value of soil moisture content in the top 500 mm of soil was measured every 4 hours for 1 year at 12 locations within a 12- by 18-m plot. The system functioned well except when the air temperature dropped below −15°C, which caused the data logger tape recorder to stop. Calibrations run on undisturbed soil cores did not compare well with published curves developed for mineral soils, probably because of high soil organic matter content. The standard error of estimate of soil moisture content, indicated by the calibrations, was 0.02 cm3/cm3. The standard deviation of repeated moisture content measurements made in the field was 0.003 cm3/cm3. The effect of cable length on the TDR signal was investigated. It was found that long cables tend to attenuate the signal, ultimately making the measurement impractical. However, cable length had little effect on the calibration up to a length of 27 m. The coefficient of variation of the moisture content measurements taken at any given time ranged from 0.12 to 0.21 during the test period. As predicted by a stochastic analysis of soil moisture flow in heterogeneous soil, the spatial variability of the measurements decreased as average soil moisture increased.

Carbon Fluxes in Plant-Soil Systems at Elevated Atmospheric CO2 Levels.

Abstract: The flow of carbon from photosynthesizing tissues of higher plants, through the roots and into the soil is one of the key processes in terrestrial ecosystems. An increased level of CO2 in the atmosphere will likely result in an increased input of organic carbon into the soil due to the expected increase in primary production. Whether this will lead to accumulation of greater amounts of organic carbon in soil depends on the flow of carbon through the plant into the soil and its subsequent transfor- mation in the soil by microorganisms. In this paper the major controls of carbon trans- location via roots into the soil as well as the subsequent microbial turnover of root-derived carbon are reviewed. We discuss possible consequences of an increased CO2 level in the atmosphere on these processes.

Heterogeneity of soil and plant N and C associated with individual plants and openings in North American shortgrass steppe

Abstract: Small-scale spatial heterogeneity of soil organic matter (SOM) associated with patterns of plant cover can strongly influence population and ecosystem dynamics in dry regions but is not well characterized for semiarid grasslands. We evaluated differences in plant and soil N and C between soil from under individual grass plants and from small openings in shortgrass steppe. In samples from 0 to 5 cm depth, root biomass, root N, total and mineralizable soil N, total and respirable organic C, C:N ratio, fraction of organic C respired, and ratio of respiration to N mineralization were significantly greater for soil under plants than soil from openings. These differences, which were consistent for two sites with contrasting soil textures, indicate strong differentiation of surface soil at the scale of individual plants, with relative enrichment of soil under plants in total and active SOM. Between-microsite differences were substantial relative to previously reported differences associated with landscape position and grazing intensity in shortgrass steppe. We conclude that microscale heterogeneity in shortgrass steppe deserves attention in investigation of controls on ecosystem and population processes and when sampling to estimate properties at plot or site scales.

The Rothamsted Long-Term Experiments: Are They Still of Use?

Abstract: The Rothamsted long-term experiments-the Classicals-were started almost 150 yr ago. These experiments were originally de signed to study the N, P, K, Na, Mg, and Si needs of the field crops then grown in England. This was done by comparing these inorganic nutrients, in various combinations, with farmyard manure, the traditional source of fertility at that time. Although the questions the experiments were originally designed to answer have long been re-solved, the experiments continue to give results of interest to agron omists, ecologists, soil scientists, plant pathologists, and others. The experiments show that grain yields can be sustained (and even in creased) for almost 150 years in monocultures of wheat and barley given organic or inorganic fertilizer annually. They provide data on the long-term effects of inorganic fertilizers and organic manures on soil organic matter levels. These data have been used to test computer-based models for the turnover of organic matter in soil. Again, long-term N balances show that there are considerable inputs of N to the soil/plant system, amounting to some 30 kg N ha−1 yr−1 in unfertilized wheat and up to 65 kg ha−1 yr−1 in an arable soil reverting to woodland. These and other results are used to consider the advantages and disadvantages of long-term experiments. Wisely used, long-term experimental sites provide information on the long-term sustainability of agricultural systems that can be obtained in no other way.

Effect of surfactants at low concentrations on the desorption and biodegradation of sorbed aromatic compounds in soil

Abstract: A study was conducted to determine the effect of low concentrations of surfactants on the biodegradation of sorbed aromatic compounds in soil. The nonionic alcohol ethoxylate surfactants Alfonic 810-60 and Novel II 1412-56 increased the extent of desorption of phenanthrene from a mineral soil. Alfonic 810-60 enhanced desorption of biphenyl from this soil at one concentration tested, but Novel II 1412-56 did not. Less than 0.01{per thousand} of the added phenanthrene and biphenyl was present in solution after their introduction into an organic soil, and the surfactants did not promote desorption. The two surfactants at 10 {mu}g/g of soil markedly increased the extent of biodegradation of phenanthrene in both the mineral and the organic soil; the stimulation was greater in the organic soil. Biphenyl mineralization in the mineral soil was not affected by either surfactant, but biodegradation in the organic soil was enhanced by Alfonic 810-60 at 100 {mu}g/g. The authors suggest that surfactants at low concentrations may promote the mineralization of sorbed aromatic compounds in polluted soils, even when surfactant-induced desorption is not appreciable.

Loss on ignition and Kjeldahl digestion for estimating organic carbon and total nitrogen in estuarine marsh soils : calibration with dry combustion

Abstract: Soils (n=250) were collected from ten salt and brackish-water marshes of North Carolina and analyzed for organic matter content by loss on ignition (LOI) and Kjeldahl nitrogen (KN). Total organic carbon and total nitrogen were determined on the same samples using an elemental CHN analyzer. Regression analyses indicated that LOI and KN were excellent estimators of organic C (R2=0.990) and total N(R2=0.986), respectively, in low clay content (0–11%) marsh soils containing a wide range of soil organic C (0.1–28%) and total N (0–1.6%). A quadratic equation best described the relationship between organic C and organic matter (Organic C=0.40 [LOI] +0.0025 [LOI]2) while a linear model accurately described the relationship between total N and Kjeldahl N (Total N=1.048 [KN]−0.010). The proportion of organic C in organic matter (C/OM) increased with increasing soil organic matter content, probably as a result of aging. Young marshes, which are characterized by low soil organic content contain C/OM ratios similar to emergent vegetation (40–45%). In old organic soils (70–80% organic matter), C/OM increased to 57–60% due to accumulation of reduced organic materials.

Effect of crop rotations and cultural practices on soil organic matter, microbial biomass and respiration in a thin Black Chernozem

Abstract: The effects of crop rotations and various cultural practices on soil organic matter quantity and quality in a Rego, Black Chernozem with a thin A horizon were determined in a long-term study at Ind...

Role of manures and crop residue in alleviating soil fertility constraints to crop production: With special reference to the Sahelian and Sudanian zones of West Africa

Abstract: In the West African semi-arid tropics (WASAT), continuous cultivation leads to drastically reduced levels of soil organic matter. Such reductions in the level of soil organic matter have resulted in decreased soil productivity. The addition of organic materials either in the form of manures or crop residue has beneficial effects on the soils’ chemical and physical properties. For many of the countries in this region, the amounts of nutrients in crops and crop residue are often several orders of magnitude higher than the quantity of the same nutrients applied as fertilizers. The return of the crop residue for soil fertility improvement cannot be overstressed. It is essential that more information on the rates of organic matter decomposition as well as the many reactions between products of organic matter decomposition and the soil under WASAT conditions be made available.

Influence of mixed cropping rotations (pasture-arable) on organic matter content, water stable aggregation and clod porosity in a group of soils

Abstract: The effects of previous cropping history on soil organic matter content, aggregate stability and clod porosity were investigated on three soil types commonly used for mixed cropping in the Canterbury region of New Zealand. An index of previous cropping history (number of years under pasture or arable cropping immediately prior to sampling) and the hot water-extractable carbohydrate fraction were closely correlated with aggregate stability. Total N, organic C, acid-hydrolysable and cold water-extractable carbohydrate were moderately well correlated with aggregate stability whilst HCl- and NaOH-extractable carbohydrates were poorly correlated with aggregate stability. Aggregate stability was correlated with clod porosity when arable and pasture samples were analysed separately, but not when all soils were included. In many of the typical short-term mixed cropping rotations used in the study area the total soil organic matter content remained relatively unchanged yet microbial biomass C, hot water-extractable carbohydrate and aggregate stability increased markedly during the pasture phase and declined during the arable period. It is suggested that the increase in aggregate stability during the short-term pasture is due principally to production of binding carbohydrates (which are hot water-extractable) by the large microbial biomass present in the pasture rhizosphere. When the pasture is ploughed under the microbial biomass declines as does aggregate stability. The increase in aggregate stability following pasture establishment is considerably more rapid than the increase in clod porosity. Thus, at a similar clod porosity, pasture aggregates had a higher aggregate stability than their arable counterparts.

Effects of heavy metals from past applications of sewage sludge on microbial biomass and organic matter accumulation in a sandy loam and silty loam U.K. soil

Abstract: Amounts of microbial biomass were measured in soils from two different U.K. field experiments, one on a sandy loam (15% clay) at Luddington (Wick series) and the other on a silty loam soil (21% clay) at Lee Valley (Hamble series), where sewage sludges, mainly enriched with single metals, were applied 22 yr ago. No single metal (Zn, Cu, Ni and Cd) at or below current EC permitted total soil metal concentrations, or limits, decreased the amounts of soil microbial biomass. However, Cu at about two and a half times permitted metal limits decreased the amounts of biomass by about 40% at both sites and caused an increased accumulation of organic C and total N of about 30% in the sandy loam and about 13% in the silty loam soil. Zinc, at about the same concentration, decreased the biomass by about 40% in the sundy loam and 30% in the silty loam soil while soil organic matter accumulation increased by only 9–14%. Cadmium, at about twice current EC limits did not affect the amount of biomass or soil organic matter in the silty loam soil. Similarly, neither were affected by Ni at 2–3 times current metal limits. The amount of microbial biomass C as a percentage of total soil organic C was much lower (

Loss on Ignition and Kjeldahl Digestion for Estimating Organic Carbon and Total Nitrogen in Estuarine Marsh Soils

Abstract: Soils (n = 250) were collected from ten salt and brackish-water marshes of North Carolina and analyzed for organic matter content by loss on ignition (LOI) and Kjeldahl nitrogen (KN). Total organic carbon and total nitrogen were determined on the same samples using an elemental CHN analyzer. Regression analyses indicated that LO1 and KN were excellent estimators of organic C (R* = 0.990) and total N (R* = 0.986), respectively, in low clay content (O-11%) marsh soils containing a wide range of soil organic C (O.l-28%) and total N (O-1.6%). A quadratic equation best described the relationship between organic C and organic matter (Organic C = 0.40 [LOI] + 0.0025 [LOI]*) while a linear model accurately described the relationship between total N and Kjeldahl N (Total N = 1.048 [KN] - 0.010). The proportion of organic C in organic matter (C/OM) increased with increasing soil organic matter content, probably as a result of aging. Young marshes, which are characterized by low soil organic content contain C/OM ratios similar to emergent vegetation (40-45%). In old organic soils (70-80% organic matter), C/OM increased to 57-60% due to accumulation of reduced organic materials.

A soil sulfur test for pastures and crops.

Abstract: Soil testing for S has generally been unsuccessful when using extractants that remove only sulfate from the soil. An assessment of a range of extractants to predict S status was undertaken on soil samples taken from 18 field trials in northern N.S.W. The extractants were water, 0.01M monocalcium phosphate (MCP) and 0.5M NaHCO3, 0.25 M KCl heated for 3 h at 100, 80, 40, or 25°C. The highest correlation between soil S test level and % maximum yield was found in the 40°C KCl extractant (r2 = 0.73). This compares with an r2 value of 0.47 for the widely used MCP extractant. A study using a soil from a pot experiment where rice was grown showed that the KCl extract removed more S from the HI reducible (ester sulfate) fraction than did MCP. This S fraction is believed to be important in supplying S to plants. A comparison of the specific radioactivity of soil extractants and rice plants confirmed that the KCl 40°C extract removes S from similar soil pools as do plants. The procedure is recommended for wider evaluation.

Short- and long-term effects of the endogeic earthworm Millsonia anomala (Omodeo) (Megascolecidæ, Oligochæta) of tropical savannas, on soil organic matter

Abstract: This study aimed to establish the effects of Millsonia anomala, a tropical geophagous earthworm common in the humid savannas of Lamto (Ivory Coast), on soil organic matter dynamics over different time scales under laboratory conditions. The texture of casts produced by the worms fed on a shrub savanna soil was not significantly different from that of the soil, which showed that M. anomala ingested soil particles without selection. Physical fractionation of soil organic matter showed that the coarse organic fraction (250–2000 μm) was depleted by 25–30% in fresh casts compared to the control noningested soil; this was mainly due to a fragmentation of coarse organic debris. Incubation of casts and a 2-mm sieved control soil under laboratory conditions for more than 1 year showed that the C mineralisation rate was almost four times lower in the casts (3% year-1) than in the control soil (11% year-1). We therefore concluded that on a long time scale M. anomala populations may significantly reduce the decomposition rate of soil organic matter in Lamto savannas.

Grazing impacts on litter and soil organic matter in mixed prairie and fescue grassland ecosystems of Alberta.

Abstract: Impacts of long-term cattle grazing on litter and soil organic matter were assessed in mixed prairie, parkland fescue, and foothills fescue grasslands of Alberta, Canada. Grazing regimes were of light to very heavy intensities, grazed early, late, and continuously during the growing season. Litter and soil organic matter were sampled in O.l-rnz quadrats and removed as live vegetation, standing Utter, fallen litter, and soil organic matter. Litter and organic matter samples were air dried and sorted by size using sieves and an automatic sieve shaker. Organic carbon content was determined by thermal oxidation. Ground cover was determined using point frames, and heights of standing litter and fallen litter were measured. Heavy intensity and/or early season grazing had greater neptive impacts on litter and soil organic matter than did light intensity and/or late season grazing. Under the former regimes there were significant reductions in heights of standing and fallen litter, decreases in live vegetative cover and organic matter mass, and increases in bare ground. More large particle-sized organic matter, particularly standing litter, occurred in controls than in grazed treatments since it would not be removed or trampled by grazing animals. More medium and small particle-sized organic matter occurred in grazed treatments than in ungrazed controls since vegetation likely decomposed more rapidly when it was trampled and broken down as animals grazed.

Effect of crop rotations and fertilization on soil organic matter and some biochemical properties of a thick Black Chernozem

Abstract: The effects of crop rotation and various cultural practices on soil organic matter and some biochemical characteristics of a heavy-textured, Orthic Black Chernozem with a thick A horizon were deter...