Showing papers on "Soil organic matter published in 1988"

Dynamics of C, N, P and S in grassland soils: a model

Abstract: We have developed a model to simulate the dynamics of C, N, P, and S in cultivated and uncultivated grassland soils. The model uses a monthly time step and can simulate the dynamics of soil organic matter over long time periods (100 to 10,000 years). It was used to simulate the impact of cultivation (100 years) on soil organic matter dynamics, nutrient mineralization, and plant production and to simulate soil formation during a 10,000 year run. The model was validated by comparing the simulated impact of cultivation on soil organic matter C, N, P, and S dynamics with observed data from sites in the northern Great Plains. The model correctly predicted that N and P are the primary limiting nutrients for plant production and simulated the response of the system to inorganic N, P, and S fertilizer. Simulation results indicate that controlling the C:P and C:S ratios of soil organic matter fractions as functions of the labile P and S levels respectively, allows the model to correctly simulate the observed changes in C:P and C:S ratios in the soil and to simulate the impact of varying the labile P and S levels on soil P and S net mineralization rates.

Controls on Natural Nitrogen-15 and Carbon-13 Abundances in Forest Soil Organic Matter

Abstract: We used δ 15 N and δ 13 C measurements to study formation and decay of soil organic matter in surface soils of two oak (Quercus spp.) forests in Wisconsin. There were two controls of soil isotopic compositions: new litter inputs and overall isotopic fractionation during decomposition. Litter inputs lowered soil δ 15 N and δ 13 C values while decomposition increased δ 15 N and δ 13 C values. Leaf and root litter inputs averaged −3.8 and −1.6‰ δ 15 N and −27.3 and −28.2‰ δ 13 C, respectively. Field experiments showed that low surface soil δ 15 N and δ 13 C values resulted when litter inputs were high. Laboratory experiments showed that overall isotopic fractionation during decomposition left residual soil N and C enriched in 15 N and 13 C, and could explain the high δ 15 N and δ 13 C values observed in deeper forest soils (+5.9‰ δ 15 N and −23.6‰ δ 13 C for 10 to 20 cm soils)

Earthworm activities and the soil system.

Abstract: Earthworms find in soil the energy, nutrient resources, water and buffered climatic conditions that they need. According to the food resource they exploit and the general environmental conditions, earthworms can be grouped into different functional categories which differ essentially in morphology, size, pigmentation, distribution in the soil profile, ability to dig galleries and produce surface casts, demographic profiles and relationships with the soil microflora. Soil characteristics are both the determinant and the consequence of earthworm activities, since these animals greatly influence the functioning of the soil system. When present, they build and maintain the soil structure and take an active part in energy and nutrient cycling through the selective activation of both mineralization and humification processes. By their physical activities and resultant chemical effects, earthworms promote short and rapid cycles of nutrients and assimilable carbohydrates. Thus earthworms represent a key component in the biological strategies of nutrient cycling in soils and the structure of their communities gives a clear indication of the type of soil system that they inhabit.

Tropical Forests and the Global Carbon Cycle

Abstract: New data on the three major determinants of the carbon release from tropical forest clearing are used in a computer model that simulates land use change and its effects on the carbon content of vegetation and soil in order to calculate the net flux of carbon dioxide between tropical ecosystems and the atmosphere. The model also permits testing the sensitivity of the calculated flux to uncertainties in these data. The tropics were a net source of at least 0.4 x 1015 grams but not more than 1.6 x 1015 grams of carbon in 1980, considerably less than previous estimates. Decreases in soil organic matter were responsible for 0.1 x 1015 to 0.3 x 1015 grams of the release, while the burning and decay of cleared vegetation accounted for 0.3 x 1015 to 1.3 x 1015 grams. These estimates are lower than many previous ones because lower biomass estimates and slightly lower land clearing rates were used and because ecosystem recovery processes were included. These new estimates of the biotic release allow for the possibility of a balanced global budget given the large remaining uncertainties in the marine, terrestrial, and fossil fuel components of the carbon cycle.

Attenuating organic contaminant mobility by soil modification

Abstract: Low organic matter clays, soils and aquifer materials have very little sorptive capability for common groundwater contaminants. Here we use organic cations of the form [(CH3)3NR]+ to displace naturally occurring exchange ions resulting in significantly higher organic matter contents, and greatly enhanced sorptive properties for nonionic organic solutes. The organic phase derived from exchanged hexadecyltrimethylammonium, where R is a C-16 hydrocarbon, behaved as a powerful partitioning medium that was 10 to 30 times more effective on a unit weight basis than natural soil organic matter for removing benzene, dichlorobenzene and perchloroethene from water. This simple soil modification might be used to improve the retardation capabilities of low organic matter soils and aquifer materials, and to enhance the containment capabilities of clay landfill liners and bentonite slurry walls.

The Biogeochemistry of Phosphorus Cycling and Phosphorus Availability Along a Desert Soil Chronosequence

Abstract: The biogeochemistry ofthe weathering, landscape movements, and chemical transformations of phosphorus and its availability to plants were examined in a chrono- sequence of soils developed from quartz monzonite alluvium in southern New Mexico. Total P in the soil profile decreased with increasing soil age and was removed from the ecosystem as readily as the most easily leachable base cations. Although Ca-bound forms of P decreased with increasing soil age, Ca-P remained the single largest fraction of total P in all soils. In contrast, Fe- and Al-bound P was a very small percent of total P in all soils. There was little evidence for the stabilization of P by soil organic matter within this ecosystem; both soil organic P and microbial P represented very small pools of total soil P. Phosphorus availability, measured by in situ resin bags, was not well correlated with soil age or total soil P, and P concentrations in shrub tissues did not reflect changes in forms or total amounts of soil P. The biogeochemical cycle of P in this system differs sharply from that in a more mesic, forested system, where fixation by iron and aluminum oxides and biologic activity play more dominant roles in the conservation of P within the ecosystem.

Long-term annual manure applications increase soil organic matter and nitrogen, and decrease carbon to nitrogen ratio

Abstract: The effects of long-term annual applications of cattle (Bos taurus) feedlot manure on the accumulation, decomposition (amounts and rates), and movement of organic matter (OM) and Kjeldahl-determined N (total N) in soil were determined. Manure was applied annually since 1973 at three different levels to nonirrigated and irrigated Dark Brown Chernozemic (Typic Haploborolls) clay loam soil. Significant increases in soil OM and total N content in the first 8 and 6 yr, respectively, as affected by the level of manure application, were limited to the surface 30 cm of soil of the nonirrigated and irrigated land. Tillage did not affect the amount of OM and total N accumulated in the soil, but it did affect their distribution within the 0 to 30-cm depth, which is attributed to placement during incorporation. The accumulation of OM and total N were similar under nonirrigated and irrigated conditions. Manure (C/N ratio of ca. 10.2) lowered the C/N ratio of the soil (ca. 8.2) by small amounts. The accumulation of OM and total N was described by a Michaelis-Menten type of function. A response surface was generated for the accumulation of OM and total N with increasing levels and years of manure application, from which the rates of accumulation and decomposition were derived. The rates of accumulation decrease with years of application such that after two or three decades increases will be small. The model can be used to develop general guidelines for use and disposal of feedlot manure under similar conditions.

Phosphorus in soil, water and sediment: an overview

Abstract: The geochemistry, availability and abundance of different forms of phosphorus in soil, water and sediments are reviewed. The present knowledge of phosphorus pathways in ecosystems and their regulation is discussed.

The effect of parent material and soil development on nutrient cycling in temperate ecosystems

Abstract: The parent material of a soil determines the original supply of those nutrient elements that are released by weathering and influences the balance between nutrient loss and retention. Organic acids and exudates produced by microorganisms and plants enhance the weathering of minerals and the release of nutrients. Nutrients may be stored in organic cycles or as ions adsorbed to clay and organic matter. Nutrients are lost mainly by leaching, both as dissolved ions and when associated with soluble organic components. Soil formation evidently affects these processes and modifies the environment at different depths as soil horizons develop. Strong interactions between mineral and organic colloids occur where most residues are added below ground, as in grasslands, or mixed with mineral soil by faunal activity, as in some forests. These systems tend to be nutrient conserving. The addition of organic residues to the soil surface often results in slow decomposition, the tie-up of many nutrients in biologically resistant humic materials, and the generation of organic acids that are active in leaching and chelation. These soils tend to lose nutrients by leaching and become strongly acidic with time. Leaching is strongest in uplands with net downward flows to deep water tables, and may be dampened or obviated in lowlands with strong upward fluxes due to artesian pressure or capillary rise from a water table that is close to the surface. Pedogenic features such as clayeyB horizons or duripans may alter water flow. Simonson's concepts that all basic soil-forming processes occur to some degree in all soils are critical to developing models describing soil formation and nutrient cycles.

Nutrient mobility in variable- and permanent-charge soils

Abstract: Variable-charge (v-c) and permanent-charge (p-c) soils differ fundamentally with regard to many nutrient-cycling processes. Variable-charge soils are more common in the tropics than in temperature zones because their formation requires desilication, which proceeds fastest in warm, moist climates. The dynamics of nutrient mobility tend to be more complex in v-c than in p-c soils. For example, theory predicts that, as pH of v-c soils decreases, cation exchange capacity (CEC) also decreases and anion exchange capacity (AEC) increases. If AEC exceeds CEC, cations such as ammonium and potassium will be more mobile than anions such as nitrate; this is the reverse of the situation in p-c soils, on which most of our knowledge of nutrient cycling is based. Variable-charge surfaces sorb phosphorus, creating plant nutritional problems throughout large areas of the humid tropics. Desilication, the same process that creates v-c surfaces, results also in stable aggregation, creating soils that retain water, yet drain rapidly and resist erosion. The Soil Taxonomy system incorporates information on mineralogy, texture, and organic matter content, and therefore provides insights into patterns of charge chemistry and nutrient cycling across a wide range of soil types.

Chemical composition of the organic matter in forest soils: 1. forest litter

Abstract: The organic chemical composition of three different forest litter types (spruce, beech, ash) is characterized by comparing results obtained from (1) wet chemical degradations, (2) CPMAS 13C NMR spectros-copy, and (3) pyrolysis-field ionization mass spectrometry (Py-FIMS). From CPMAS 13C NMR spectros-copy, the litter layers consist of 17 to 23% alkyl-C, 52 to 56% O-alkyl-C, 15 to 23% aromatic carbon, and 5 to 10% carboxyl-C. The wet chemical methods account for 49 to 59% of the total organic carbon in the litter layers. More specifically, proteins and extractable lipids account for 30 to 40% of the alkyl-C. Polysaccharides and lignin side chains account for 74 to 78% of the O-alkyl-C, and lignin-derived phenols, determined by CuO-oxidation, account for 26 to 71% of the aromatic carbon. The identification of the organic litter constituents is substantiated qualitatively by Py-FIMS. All three methods give similar results for poly-saccharides, which make up 40 to 50% of the organic matter of litter. Furthermore, Py-FIMS indicates that part of the unknown alkyl-C is present in the form of bound, nonextractable fatty acids.

Evaluation of soil respiration characteristics to assess heavy-metal effects on soil-microorganisms using glutamic-acid as a substrate

Abstract: Computerized continuous monitoring of soil respiration rates before and during glutamic acid decomposition in heavy metal polluted soils was used to determine four microbial parameters: basal respiration rate, substrate induced respiration rate, lag time before the exponential increase of the soil respiration rate and the specific respiration increment during the exponential phase. Both smelter- and laboratory-contaminated soils were studied. Basal respiration rate was the parameter most inhibited (54–77%) by heavy metal contamination. Increased soil moisture resulted in increased basal respiration rate, irrespective of pollution level. The substrate-induced respiration rate after the addition of glutamic acid was strongly correlated with the basal respiration rate (r = 0.85−0.95). The change in specific respiration increment was not related to metal contamination but increased with increasing soil moisture, with an optimum at about 250% H2O based on soil organic matter (oven-dried). Lag time was the parameter best correlated with smelter-induced metal contamination (r = 0.64 and 0.75). Unlike the three other parameters, the lag time was unaffected by soil moisture, irrespective of contamination level. (Less)

Phosphorus cycling in wheat-pasture rotations. II. The role of the microbial biomass in phosphorus cycling.

Abstract: The incorporation of phosphorus derived from fertilizer and plant residues into the soil microbial biomass was studied under field conditions by using isotopic double labelling. The 33P-labelled medic residues (Medicago truncatula cv. Paraggio) and 32P-labelled fertilizer were added to a solonized brown soil (Calcixerollic xerochrept) before sowing of a wheat crop ( Triticum aestivum cv. Warigal). Amounts of 31P, 32P and 33P in the microbial biomass were determined at 0, 7, 18, 32, 46, 61, 81 and 95 days after sowing of the wheat. Throughout the experiment, amounts of 31P in the microbial biomass were closely related to gravimetric soil water content, with a large and rapid increase in the amount of 3 1 ~ in the microbial biomass being observed in the first 7 days after wetting of the (initially) dry soil. Due to banding of the fertilizer at sowing, little (<5%) of the 32P was recovered in the microbial biomass throughout the experiment. Of the 33P applied in the medic residues, 22-28% was recovered in the microbial biomass. Most of the P taken up by the microbial biomass was derived from native soil P (i.e. not added that season).

Evaluation of a Method to Predict Nitrogen Mineralized from Soil Organic Matter Under Field Conditions

Abstract: Methods to estimate the amount of N mineralized from soil organic matter are needed for accurate fertilizer recommendations. We conducted laboratory and field studies to evaluate the method of Stanford and Smith for predicting N mineralized under field conditions. Soil samples were incubated to determine their N mineralization potentials and first-order rate constants of mineralization. To predict N mineralized in the field, the rate constants of mineralization were adjusted by soil temperature, and the amount of N mineralized predicted with the N mineralization potentials and adjusted rate constants were further adjusted by soil water content. Nitrogen mineralized in the field was measured in sorghum [Sorghum bicolor (L.) Moench] plots established on Haynie (coarse-silty, mixed, calcareous, mesic Mollic Udifluvent), Kahola (fine-silty, mixed, mesic Cumulic Hapludoll), and Richfield (fine, montmorillonitic, mesic Aridic Argiustoll) soils in 1983 and 1984. Nitrogen mineralized was also measured in fallow plots on Haynie and Wymore (fine, montmorillonitic, mesic Aquic Argiudoll) soils in 1984. The method only accurately predicted the amount of N mineralized in 104 d in fallow plots on Haynie soil. In all other cases, the method significantly overpredicted by 67 to 343% the amounts of N mineralized in the field. Among possible causes for the overpredictions may be an improper soil water content factor and the drying and sieving of the samples before incubation. Contribution no. 87-432-J from the Kansas Agric. Exp. Stn.

Two mechanisms for age‐hardening of soil

Abstract: SUMMARY Soil samples from Germany, Israel and USA were moulded at water contents around the lower plastic limit and compacted with uniaxial pressures c. 20-200 kPa. The samples were stored at constant water content. At intervals after moulding, the strengths of sub-samples were measured with a small penetrometer. The soils showed increases in strength with time. Two types of behaviour were observed and explained by a simplified theory for soil strength. With the German and Israel soils, penetrometer strength increased by the same absolute amount irrespective of compaction pressure. This indicates that new particle-particle bonds were being formed at a rate which was not affected by compaction. With the USA soils, the ratio of penetrometer strength/initial strength increased with time and was independent of compaction pressure. This indicates that existing particle-particle bonds were being reinforced by a cementation mechanism. Evidence is presented which suggests that age-hardening by this second mechanism may be inhibited by soil organic matter.

The Role of Mulch and its Architecture in Modifying Soil Temperature

Abstract: Both the quantity and architecture of a surface mulch affect its performance in modifying the soil microenvironment. In this paper, temperature under two simple mulch architectures is compared and contrasted with that of bare soil in a tropical environment. In mulch treatments the quantities of mulch per unit area were similar, but elements in one treatment were horizontal (forming a 5 cm layer) while in the other they were vertical (forming a 22 cm layer). Temperatures were recorded for several days as the soil dried following a storm which saturated the mulch and surface soil. The bare soil dried more rapidly than that with mulch, so that by the fourth day its hourly maximum surface temperature was 8°C higher, and that at 2 5 cm depth was 3°C higher, than soil temperatures under the mulch. Significant differences in soil temperatures under the two mulch treatments only appeared several days later, as subtle differences in the partitioning of energy by the two mulch canopies became more apparent with drier conditions. By the twelfth day, the maximum surface temperature under the vertical mulch was 7°C higher than that under the horizontal mulch. Minimum soil temperatures were never more than 2.5°C different between the bare and mulched treatments and converged with drying. In both mulch treatments, the mulch elements near the soil surface experienced greater temperature extremes than those at the top of the mulch layer. The range in element temperature was slightly greater in the horizontal mulch treatment than in the vertical mulch treatment, where the element temperatures were more closely tied to air temperatures. The first few days following rain are crucial for seedling establishment in the semi-arid tropics and it appears from this study that mulch architecture is of minor importance during this period.

Mineralization of 14C-labelled humic acids and of humic-acid bound 14C-xenobiotics by Phanerochaete Chrysosporium

Abstract: Humic compounds are generally stabilized in soil against microbial decomposition by their complex polymer structure and their adsorption to the inorganic soil matrix Also the great resistance to degradation of “bound” residues from plant protection agents is believed to be largely related to the incorporation of the parent chemical or its partial degradation products into humic polymers Changes in the environment or in management practices, however, can lead to an enhanced degradation of both soil organic matter or “bound” residues Obviously, these organic matter components then become available to microbes and soil organisms which degrade lignin are very likely involved in the degradation process We determined to what extent P chrysosporium, one of the most active ligninolytic fungi, could mineralize humic acids, “bound” components from xenobiotics in humic acids, phenolic model polymers and the free xenobiotic chemicals For the investigations 14C-labelled humic acids, humic acids with 14C-labelled plant protection chemicals or model polymers from phenols together with 14C-constituents were utilized for degradation studies After 18 d in culture solutions, the fungus released about 13–56% of the labelled C as CO2 in most of the tests Some of the free compounds appeared to be toxic to the fungus High nutrient N-concentrations in the culture solutions tended to reduce decomposition rates

Elevational and age gradients in hawaiian montane rainforest: foliar and soil nutrients

Abstract: Soils and plants were sampled along an elevational gradient from 265-1675 m on a 133-and a 3100-year-old lava flow on Mauna Loa, Hawai'i. Soil organic matter and nutrients accumulated more rapidly at low elevation on the young flow, but reached higher levels at higher elevation on the old flow. Foliar nitrogen and phosphorus concentrations were less and specific leaf weight greater for Metrosideros polymorpha leaves collected at high versus low elevations and on the young versus the old flow. Foliar δ13C was strongly correlated with specific leaf weight across the range of sites sampled.