Controlled Moisture Conditions Research Articles

Soil burial-induced degradation of cellulose films in a moisture-controlled environment

In this study, the biodegradability of cellulose films was evaluated in controlled-moisture soil environments. The films were prepared from low-quality cotton fibers through dissolution in DMAc/LiCl, casting, regeneration, glycerol plasticization, and hot-pressing. Two soil burial degradation experiments were conducted in August 2020 (11th August to 13th October) and March 2021 (24th March to 24th July) under controlled moisture conditions to assess the biodegradation behavior of cellulose films. The films were retrieved from soil beds at seven-day intervals, and morphological and physicochemical changes in the films were investigated. The results indicated that the cellulose films exhibited gradual changes starting on Day 7 and major changes after Day 35. Stereomicroscopy images showed the growth and development of fungal mycelia on the surface of the films, and FTIR spectroscopy confirmed the presence of biomolecules originating from microorganisms. The tensile strength and elongation of cellulose films were significantly reduced by 64% and 96% in the first experiment and by 40% and 94% in the second experiment, respectively, during the degradation period. Degradation also significantly impacted the thermal stability (14% and 16.5% reduction, respectively, in the first and second studies) of the films. The cellulose-based films completely degraded within 63 days in late summer and 112 days in spring. This study demonstrates that, unlike synthetic plastics, films prepared from low-quality cotton fibers can easily degrade in the natural environment.

Raman micro-spectroscopy of two types of acetylated Norway spruce wood at controlled relative humidity.

Water is a key element for wood performance, as water molecules interact with the wood structure and affect important material characteristics such as mechanical properties and durability. Understanding wood-water interactions is consequently essential for all applications of wood, including the design of wood materials with improved durability by chemical modification. In this work, we used Raman micro-spectroscopy in combination with a specially designed moisture chamber to map molecular groups in wood cell walls under controlled moisture conditions in the hygroscopic range. We analyzed both untreated and chemically modified (acetylated to achieve two different spatial distributions of acetyl groups within the cell wall) Norway spruce wood. By moisture conditioning the specimens successively to 5, 50, and 95% relative humidity using deuterium oxide (D2O), we localized the moisture in the cell walls as well as distinguished between hydroxyl groups accessible and inaccessible to water. The combination of Raman micro-spectroscopy with a moisturizing system with deuterium oxide allowed unprecedented mapping of wood-water interactions. The results confirm lower moisture uptake in acetylated samples, and furthermore showed that the location of moisture within the cell wall of acetylated wood is linked to the regions where acetylation is less pronounced. The study demonstrates the local effect that targeted acetylation has on moisture uptake in wood cell walls, and introduces a novel experimental set-up for simultaneously exploring sub-micron level wood chemistry and moisture in wood under hygroscopic conditions.

Velocity of Meloidogyne ethiopica second‐stage juveniles in sandy soil under several soil moisture conditions

AbstractCalculating the velocity and migration of plant‐parasitic nematodes in soil is important for understanding individual roles in nematode populations. Tracking individual nematodes in the soil is difficult, and any marking system can alter the behavior of second‐stage juvenile (J2) nematodes. This study examined the velocity of Meloidogyne ethiopica J2s under different soil moisture conditions and proposed a maximum migration distance. Evaluations considered 16 velocity categories (distances of 1.5, 4.5, 9.5, and 14.5 cm; experimental periods of 3, 6, 16, and 26 d) and four moisture ranges (40–55, 55–70, 70–85, and 85–100%) in pots with sandy soil under controlled temperature and moisture conditions. The weighted average velocity of J2 specimens that reached the roots was 70–75 μm h−1, and the maximum recorded velocity was 378 μm h−1. The fastest average velocities were 100 μm h−1 (Test 1) and 89 μm h−1 (Test 2). The average velocity at 85–100% soil moisture was very similar to the overall weighted average velocity of M. ethiopica J2s because most movement of the J2 specimens occurred at higher soil moisture ranges. Few J2s moved in the 40–55% soil moisture range. At slow velocities (24, 39, and 72 μm h−1), the number of J2s reaching the roots was highly correlated with higher soil moisture. The majority of M. ethiopica J2s did not move or moved at velocities slower than 24 μm h−1, implying that unless the plant roots were near the nematode, they will not be infested.

Selected qualitative parameters above-ground phytomass of the Lenor-first Slovak cultivar of Festulolium A. et Gr.

Article Details: Received: 2018-10-04 | Accepted: 2018-11-06 | Available online: 2019-01-31 https://doi.org/10.15414/afz.2019.22.01.13-16 The aim of this experiment was to compare selected qualitative parameters in above-ground phytomass of the first Slovak cultivar of Festulolium A et. Gr. cv. Lenor in compare earlier registered cultivars Felina and Hykor. The pot experiment was conducted at the Demonstrating and research base of the Department of Grassland Ecosystems and Forage Crops, Slovak Agricultural University in Nitra (Slovak Republic) with controlled moisture conditions (shelter) in 2017. Content of nitrogen, phosphorus, potassium, calcium, magnesium, crude fiber and water soluble carbohydrates were determined from dry above-ground phytomass of grasses. The significantly highest (P<0.05) nitrogen content in average of cuts was in above-ground phytomass of Felina (30.3 g.kg -1 ) than Hykor (25.4 g.kg -1 ) and new intergeneric hybrid Lenor (25.0 g.kg -1 ). At the least content of phosphorus was found out in hybrid Lenor (3.4 g.kg -1 ). In average of three cuts was the least concentration of potassium in new intergeneric hybrid Lenor (5.8 g.kg -1 ). At least content of calcium was found out in hybrid Lenor (7.0 g.kg -1 ). Magnesium concentration of was from 5.0 g.kg -1 (Hykor) to 6.1 g.kg -1 (Felina). Higher (P<0.05) fiber content in average of cuts was in above-ground phytomass of Lenor (27.0 %) and Hykor (26.5%) than Felina (24.0%). The highest concentration of water soluble carbohydrates has in Hykor and Lenor (3.5%). Keywords: grass hybrids, festulolium, quality

Growth-Production Parameters of the First Slovak Cultivar of Festulolium A. et Gr.

The aim of this experiment was to compare growth and production parameters of the first Slovak cultivar of xFestulolium with Felina and Hykor. The experiment was conducted at the Demonstrating and research base of Department of Grassland Ecosystems and Forage Crops, Slovak Agricultural University in Nitra (Slovak Republic) with controlled moisture conditions (glass house) in 2017 (one year pot experiment). We compared new intergeneric hybrid Lenor with Felina and Hykor. In the experiment were evaluated average height (mm) and dry matter (DM) yields (g). New intergeneric hybrid Lenor was in every cut highest (P < 0.05) (59.57 mm) in compare with controlled varieties Felina (47.89 mm) and Hykor (47.07 mm). Lenor had higher dry matter yields than Felina and Hykor in the first and second cut. In the 3rd cut were not observed significant differences in dry matter yields. The highest DM yields were measured by Hykor (2.82 g). In sum of three cuts reached Lenor highest dry matter yield (4.99 g). This measured value was higher (P < 0.05) compared with Felina’s production.

Peat soils stabilization using Effective Microorganisms (EM)

Peat soil is known as geotechnical problematic soil since it is the softest soil having highly organic and moisture content which led to high compressibility, low shear strength and long-term settlement. The aim of this study was to obtain the stabilized peat soils using the Effective Microorganisms (EM). The volume of EM added and mixed with peat soils varied with 2%, 4%, 6%, 8% and 10% and then were cured for 7, 14 and 21 days. The experiment was done for uncontrolled and controlled moisture content. Prior conducting the main experiments, the physical properties such as moisture content, liquid limit, specific gravity, and plastic limit etc. were measure for raw peat samples. The Unconfined Compressive Strength (UCS) test was performed followed by regression analysis to check the effect of EM on the soil strength. Obtained results have shown that the mix design for controlled moisture contents showed the promising improvement in their compressive strength. The peat soil samples with 10% of EM shows the highest increment in UCS value and the percentage of increments are in the range of 44% to 65% after curing for 21 days. The regression analysis of the EM with the soil compressive strength showed that in controlled moisture conditions, EM significantly improved the soil stability as the value of R2 ranged between 0.97 – 0.78. The results have indicated that the addition of EM in peat soils provides significant improving in the strength of the soil as well as the other engineering properties.

Dielectric Losses of Paper in the THz Domain: Literature Review, Needs for Future Research, and Prospective Solutions

High frequency paper‐based electronics is developing fast, with smart yet low cost applications in view. However, the dielectric losses of paper remain a difficult hurdle to overcome. First, the literature on the topic is reviewed and the contributions from moisture, air, mineral filler, and wood constituents to dielectric losses are highlighted. Then, the guidelines for future research are defined, including the need for systematic comparisons in controlled moisture conditions. In an effort to produce low loss materials for paper‐based electronics, it is proposed here to impregnate paper with a low loss substance, after removing residual water.

Dependence of Soil Organic Carbon on available Iron and Manganese Concentrations in Submerged Rice Soils

Dependence of Soil Organic Carbon on available Iron and Manganese Concentrations in Submerged Rice Soils Effect of soil submergence on changes in soil organic C (SOC) and DTPA-extractable Fe and Mn and their interrelationship was studied in three texturally-different soils viz. loamy sand, clay loam and silty clay traditionally grown to rice-wheat system. Laboratory incubation experiments were conducted for 120 d under controlled temperature and moisture conditions. Soil organic C increased with incubation period up to 30-45 d and declined sharply thereafter. Similarly, concentration of DTPA-Fe was highest at 30 d and decreased sharply thereafter. However, DTPA-Mn concentration was the highest at 15 and 30 d of incubation, under submerged and field capacity moisture regimes, respectively. Soils incubated under submerged conditions exhibited higher SOC, DTPA-Fe, and DTPAMn than those incubated at field capacity moisture. In all the three soils under submerged conditions SOC, DTPA-Fe and Mn were higher at 40o C followed by 30o C and 20o C temperature. Irrespective of soil and incubation temperature, values of these variables did not change with incubation of air dry soil. The concentration of DTPAFe and Mn showed positive relationship with SOC concentration at submerged and field capacity moisture regimes. Increase in SOC with submergence was considered to be due to an increase in DTPA-Fe and Mn suggesting the need for using some chelating agents to remove their interference in SOC determination by wet digestion method..

Measuring the relative hydrogen-bonding strengths of alcohols in aprotic organic solvents.

Voltammetric experiments with 9,10-anthraquinone and 1,4-benzoquinone performed under controlled moisture conditions indicate that the hydrogen-bond strengths of alcohols in aprotic organic solvents can be differentiated by the electrochemical parameter ΔEp (red) =|Ep (red(1)) -Ep (red(2)) |, which is the potential separation between the two one-electron reduction processes. This electrochemical parameter is inversely related to the strength of the interactions and can be used to differentiate between primary, secondary, tertiary alcohols, and even diols, as it is sensitive to both their steric and electronic properties. The results are highly reproducible across two solvents with substantially different hydrogen-bonding properties (CH3 CN and CH2 Cl2 ) and are supported by density functional theory calculations. This indicates that the numerous solvent-alcohol interactions are less significant than the quinone-alcohol hydrogen-bonding interactions. The utility of ΔEp (red) was illustrated by comparisons between 1) 3,3,3-trifluoro-n-propanol and 1,3-difluoroisopropanol and 2) ethylene glycol and 2,2,2-trifluoroethanol.

Oxygen transfer in solid-state cultivation under controlled moisture conditions.

The aim of this work was to study oxygen transfer as a function of the initial moisture content in solid-state cultivation under controlled moisture conditions. The use of controlled moisture conditions prevents drastic changes in the medium during cultivation, allowing the use of a pseudo-steady-state model to estimate the overall oxygen mass transfer coefficient (K L a) in the biofilm around the solid particles. Drechslera (Helminthosporium) monoceras, an aerobic mold that produces allergenic proteins, was cultured on wheat bran in a packed bed column bioreactor. The bed height (30 mm) and air flow rate (0.4 L/min) were selected to implement moisture control. The results show that there is an optimal moisture content (35 %) at which a lower biofilm thickness and packing of the bed improves K L a. However, a higher biomass growth was obtained at 45 % moisture. The different patterns of biomass growth demonstrate the importance of the balance between aerial and film growth in solid-state cultivation. These results contribute to the understanding of oxygen transfer in solid fermentation, optimization of processes, and production of allergen extracts from D. (Helminthosporium) monoceras biomass.

Mercury emissions from flooded soils and sediments in Germany are an underestimated problem: challenges for reliable risk assessments and management strategies

Environmental pollution by mercury is a world-wide problem. Particularly floodplain ecosystems are frequently affected. One example is the Elbe River in Germany and its catchment areas; large amounts of Hg from a range of anthropogenic and geogenic sources have been accumulated in the soils of these floodplains. They serve as sink for Hg originating from the surface water of adjacent river. Today, the vastly elevated Hg contents of the floodplain soils at the Elbe River often exceed even the action values of the German Soil Conservation Law. This is especially important as Hg polluted areas at the Elbe River achieve several hundred square kilometres. Thus, authorities are coerced by law to conduct an appropriate risk assessment and to implement practical actions to eliminate or reduce environmental problems. A reliable risk assessment particularly with view to organisms (vegetation as green fodder and hay production, grazing and wild animals) to avoid the transfer of Hg into the human food chain, requires an authentic determination of Hg fluxes and their dynamics since gaseous emissions from soil to atmosphere are an important pathway of Hg. However, reliable estimates of Hg fluxes from the highly polluted floodplain soils at the Elbe River and its tributaries, and its influencing factors are scarce. For this purpose, we have developed a new method to determine mercury emissions from soils at various sites. Our objectives were i) to quantify seasonal variations of total gaseous mercury (TGM) fluxes for floodplain soils at the Elbe River, ii) to provide insights into physico-chemical processes regulating these TGM fluxes, and iii) to quantify the impacts of the controlling factors soil temperature and soil water content on Hg volatilization from a typical contaminated floodplain soil within soil microcosm experiments under various controlled temperature and moisture conditions. Our study provides insight into TGM emissions from highly Hg-polluted floodplain soils in Germany and that those emissions are an underestimated problem. Current needs for reliable risk assessments, the induced implications for authorities, and future challenges will be discussed. The presented data will contribute to a better understanding of seasonal dynamics of Hg fluxes and its controlling factors. This presentation should be of large interest for a wide international audience, such as environmental scientists and managers, applied ecologists, and authorities.

Comparison of Phosphate Materials for Immobilizing Cadmium in Soil

A study was conducted to compare the effects of phosphate (P) materials in reducing cadmium extractability. Seven P materials (commercial P fertilizers--fused phosphate (FP), 'fused and superphosphate' [FSP], and rock phosphate [RP]; P chemicals--Ca[H(2)PO(4)](2).H(2)O, [NH(4)](2)HPO(4), KH(2)PO(4), and K(2)HPO(4)) were selected for the test. The selected P source was mixed with Cd-contaminated soil at the rate of 0, 200, 400, 800, and 1,600 mg P kg(-1) under controlled moisture conditions at 70% of water holding capacity, then incubated for 8 weeks. FP, Ca(H(2)PO(4))(2) H(2)O, KH(2)PO(4), and K(2)HPO(4) significantly decreased NH(4)OAc-extractable Cd (plant-available form) concentrations with increasing application rates. Compared to other phosphate materials used, K(2)HPO(4) was found to be the most effective in reducing the plant-available Cd concentration in soil, mainly due to the negative charge increase caused by soil pH and phosphate adsorption. Contrary to the general information, FSP and (NH(4))(2)HPO(4) increased Cd extractability at low levels of P application (<400 mg kg(-1)), and thereafter Cd extractability decreased significantly with increasing application rate. RP scarcely had an effect on reducing Cd extractability. Ion activity products of CdHPO(4), Cd(OH)(2), and CdCO(3) analyzed by the MINTEQ program were significantly increased by K(2)HPO(4) addition, but the effect of Cd-P compound formation on reducing Cd extractability was negligible. Conclusively, the P-induced alleviation of Cd extractability can be attributed primarily to Cd immobilization due to the increase in soil pH and negative charge rather than Cd-P precipitation, and therefore, alkaline P materials such as K(2)HPO(4) are effective for immobilizing soil Cd.

Effect of extrusion under controlled temperature and moisture conditions on ileal apparent amino acid and starch digestibility in peas determined with young broilers

The objective of the experimental programme was to examine the influence of extrusion of peas under controlled temperature and moisture conditions on coefficient of ileal apparent digestibility (CIAD) of amino acids and to examine the changes to starch structure (crystallisation) and subsequent effects on CIAD of starch in young broilers. Experiment 1 used one pea cultivar (2.94 mg trypsin inhibitor units (TIU)/g DM) processed under two extrusion temperatures (exit temperatures of 70 and 140 °C) and two moisture levels (0 and 1.96l water added/h) giving a 2 × 2 factorial design (with a 5th treatment being the raw pea sample). All pea samples were added at a rate of 500 g/kg into a purified diet where peas were the only source of protein/amino acids. Processing generally led to a reduction in CIAD of amino acids but CIAD of starch for Raw, Treatments 1 and 3 (added water) was lower than that for Treatments 2 and 4 (no water) with data of 0.730, 0.808 and 0.759 vs. 0.852 and 0.834, respectively. Experiment 2 evaluated two near-isogenic lines of peas (HA5 and HB5) processed under the same conditions as for Experiment 1. Extrusion at 70 °C/addition of water had no significant effect on trypsin inhibitor activity but the inhibitor was eliminated at 140 °C with or without addition of water (P<0.001). Pea line HA5 generally had higher CIAD than HB5 (P<0.05 for cystine, lysine, leucine, histidine, alanine; P<0.01 for threonine). There were significant temperature × water addition interactions for CIAD (P<0.001 for all amino acids except methionine; P=0.006). For example, data for lysine were 0.760, 0.828, 0.860 and 0.759, respectively for 140 °C/no water, 140 °C/1.96 l/h, 70 °C/no water and 70 °C/1.96 l/h. CIAD for starch improved following processing, attributed to the loss of crsytallinity. The data indicate that peas are sensitive to high processing temperatures which are associated with a reduction in nutritive value, in terms of amino acid digestibility, for young poultry. In contrast, the results reinforce the adverse effect of crystallinity on starch digestibility and show that extrusion in the absence of water improves the digestibility of raw starches due to granular disorganisation (as evidenced by X-ray diffraction patterns) and changes in crystallinity.

Empirical predictions of plant material C and N mineralization patterns from near infrared spectroscopy, stepwise chemical digestion and C/N ratios

Prediction of carbon (C) and nitrogen (N) mineralization patterns of plant litter is desirable for both agronomic and environmental reasons. Near infrared reflectance (NIR) spectroscopy has recently been introduced in decomposition studies to characterize biochemical composition. The purpose of the current study was to use empirical techniques to predict C and N mineralization patterns of a wide range of plant materials incubated under controlled temperature and moisture conditions. We hypothesized that the richness of information in the NIR spectra would considerably improve predictions compared to traditional stepwise chemical digestion (SCD) or C/N ratios. Initially, we fitted a number of empirical functions to the observed C and N mineralization patterns. The best functions fitted with R 2=0.990 and 0.949 to C and N, respectively. The fractions of C and N mineralized at different points in time were then either predicted directly with regression functions or indirectly by prediction of the parameters of the empirical functions fitted to incubation data. In both cases, partial least squares (PLS) regressions were used and predictions were validated by cross-validations. We found that the NIR spectra (best R 2=0.925) were able to predict C mineralization patterns marginally better than the SCD fractions (best R 2=0.911), but considerably better than the C/N ratios (best R 2=0.851). In contrast, N mineralization was better predicted by SCD fractions (best R 2=0.533) than the C/N ratio (best R 2=0.497), which was better than NIR predictions (best R 2=0.446). Although the predictions with the NIR spectra were only slightly better for C and worse for N mineralization compared to SCD fractions, NIR spectroscopy still holds advantages, as it is a much less laborious and cheaper analytical method. Furthermore, exploration of the applications of NIR spectroscopy in decomposition studies has only just begun, and offers new ways to gain insights into the decomposition process.

Assessment of soil properties by organic matter and EM-microorganism incorporation

Properties of a claim loam soil, collected in Aranjuez (Madrid) and enriched with organic matter and microorganisms, were evaluated under controlled temperature and moisture conditions, over a period of three months. The following treatments were carried out: soil (control); soil + 50 t ha-1 of animal manure (E50); soil + 50 t ha-1 of animal manure + 30 L ha-1 of effective microorganisms (E50EM); soil + 30 t ha-1 of the combination of various green crop residues and weeds (RC30) and soil + 30 t ha-1 of the combination of various green crop residues and weeds + 30 L ha-1 of effective microorganisms (RC30EM). Soil samples were taken before and after incubation and their physical, chemical, and microbiological parameters analyzed. Significant increase was observed in the production of exopolysaccharides and basic phosphatase and esterase enzyme activities in the treatments E50EM and RC30EM, in correlation with the humification of organic matter, water retention at field capacity, and the cationic exchange capacity (CEC) of the same treatments. The conclusion was drawn that the incorporation of a mixture of effective microorganisms (EM) intensified the biological soil activity and improved physical and chemical soil properties, contributing to a quick humification of fresh organic matter. These findings were illustrated by the microbiological activities of exopolysaccharides and by alkaline phosphatase and esterase enzymes, which can be used as early and integrated soil health indicators.

Use of principal component analysis to assess factors controlling net N mineralization in deciduous and coniferous forest soils

Net N mineralization was studied in three different forest sites (Belgium): a mixed deciduous forest with oak (Quercus robur L. and Quercus rubra L.) and birch (Betula pendula Roth) as dominant species, a deciduous stand of silver birch (Betula pendula) and a coniferous stand of Corsican pine (Pinus nigra ssp. Laricio). The organic (F + H) layer and mineral soil at different depths (0–10, 10–20 and 20–30 cm) were sampled at three locations in the mixed deciduous forest (GE, GF1, GF2), at one location in the silver birch stand (SB) and one in the Corsican pine stand (CP). All samples were incubated over 10 weeks under controlled temperature and moisture conditions. The net N mineralization rates in the organic and upper mineral layer (0–10 cm) were found to be significantly different from the other layers and accounted for 66–95% of the total mineralization over the first 30 cm. Net N mineralization rates in the organic layer ranged from 4.2 to 27.3 mg N m–2 day–1. Net N mineralization and nitrification rates were positively correlated. For the mineral soil, net N mineralization rates decreased with depth and the upper 10 cm showed significantly higher rates, ranging from 8.9 to 33.5 mg N m–2 day–1. The rates of the 10–20 cm and 20–30 cm sublayers were similar, ranging from 1.2 to 7.4 mg N m–2 day–1. The net N mineralization rates for the total mineral layer (0–30 cm) ranged from 17.4 mg N m–2 day–1 (SB) to 36.1 mg N m–2 day–1 (CP). Both from PCA and multiple regression analysis, we could conclude that net N mineralization rates were closely related to the initial mineral N content (Ninitial). Furthermore, significant correlations were observed between the net N mineralization rate, the total carbon (TC) and NH4+-N content for the mineral layers and between net N mineralization rate, total nitrogen (TN), hemicellulose content and C/N for the organic layers.

A laser-based ultrasonic technique to measure the dependence of the bending stiffness of copy paper on moisture and temperature

A noncontact system is used to generate and detect, optically, a broadband ultrasonic pulse propagating in paper under controlled temperature and moisture conditions. The generation laser (Nd–Yag) produces a short optical pulse which is directed through an optical window on the paper sample inside an environmental chamber where temperature and relative humidity are controlled. Ultrasonic Lamb waves propagating in the paper are detected by a fiberoptic Mach–Zehnder interferometer (argon–ion laser) where the Doppler-shifted light exits the chamber through a small-core multimode fiber. The moisture content is measured by monitoring the weight of the paper sample relative to a dry sample. The dispersive nature of the A0 Lamb mode of the ultrasonic signal contains information about the bending stiffness normalized by the density and thickness of the paper averaged over the propagation path. The frequency dependence of the group velocity is found from the analytic wavelet transform of the signal (complex Morlet wavelet). [Work supported by the Department of Energy and the Institute of Paper Science and Technology.]

Decomposition of crop residues in the field: evaluation of a simulation model developed from microcosm studies

On 12 occasions during a 2-y field experiment, we determined the decomposition of barley straw, ryegrass foliage, white clover foliage, potato haulm and white cabbage leaves confined in buried mesh bags that were protected against leaching. After 1 y, 49, 18, 8, 25 and 5% of initial carbon in the five crop residues remained, respectively. The corresponding figures for nitrogen were 105, 32, 8, 36 and 11%. The data were used to evaluate a simulation model developed during previous studies of crop residue C and N turnover under controlled temperature and moisture conditions. Description of plant residue degradability and model parameter values were taken from these studies. Rate-modifying functions were then added to take account of effects of measured soil temperature and moisture. The model gave a good overall description of crop residue degradation but underestimated C release and, to a greater extent, N release during the first autumn and winter. The relatively rapid N loss during this period, suggested that low temperatures restricted microbial N immobilization more than it did gross decomposition. We hypothesized that this was caused by a reduced microbial growth yield efficiency ( E) at low temperatures. When we reduced the value of E from 0.5 (default value) to 0.2 at 2°C and below, model fit to C and N mineralization was improved substantially. Moreover, the model produced an excellent fit to remaining wheat straw C and gave a good description of N mineralization in an independent experiment, indicating that reducing the value of E was justified. The results suggested that crop residue degradability and the decomposer community were reasonably described in the model, that the rate-modifying functions of temperature, moisture and N availability were sound and that parameter values set under controlled conditions also represented field conditions, possibly with the exception of E.

Decomposition of 14C- and 15N-labelled plant material, under controlled conditions, in coniferous forest soils from a north–south climatic sequence in western Europe

The aim of this work was to clarify how decomposition kinetics and microbial biomass size and activity are controlled by humus and soil properties. The organic horizons (including Oh and A1 horizons) of seven coniferous forest soils (on siliceous and limestone parent material) from a north–south climatic sequence in western Europe from Boreal to Mediterranean climate, were incubated in laboratory under controlled temperature and moisture conditions, for 150 d, with 14C- and 15N-labelled mature low N wheat straw material. The soils represented a wide range of the major humus types. The basal respiration (soil-native CO 2 release) increased significantly in soils sampled from north to south and as the soil pH increased. 14C remaining in soils at the end of the experiment ranged from 52 to 80% of initial 14C. Significant differences were observed between humus types. A regression procedure was used to fit the sum of two exponential functions to the 14C decay curves. The mineralisation rate constant ( k a) of the labile compartment (A) varied within a narrow range (0.033 to 0.05 d −1), indicating that this fraction was essentially controlled by the quality of the added labelled plant material. The mineralisation rate constant ( k b) of the stabilised compartment (B) varied significantly over a much wider range (0.0005 to 0.0026 d −1), indicating that humus types exert strong controls on the decomposition of the recalcitrant fractions. Within each humus group, k b increased in soils sampled from north to south and was essentially controlled by the pH gradient through the climatic sequence. After 150 d, the labelled N mineralisation rates ranged from 10% in the Boreal soils to 30% in the Mediterranean soils. The size of the labelled microbial biomass (MB- 14C) was related to the humus types and the soil pH. The lowest values were obtained for Oh and acid A1 horizons from the high latitude sites and the highest for basic or neutral Mediterranean A1 horizons. A range of differently textured A1 horizons was used to examine the effect of clay and sand. The metabolically labelled respiration quotient ( qCO 2- 14C) indicated (1) an initial active phase characterised by the use of labile organic compounds; (2) a lower activity phase indicating the exhaustion of available resources and the use of recalcitrant material. ( qCO 2- 14C) was related to the humus types. The calculated metabolic efficiencies were generally high (0.2 to 0.5) when labile material was used as substrate. Decomposition of more resistant compounds reduced the efficiency to values <0.1, indicating higher energy requirements per unit of synthesised biomass. Eleven decomposition variables were analysed by means of correspondence analysis. The descriptors of soil properties were used as additional variables. The seven humus types were clearly separated. The ordination of the major decomposition variables were highly related to soil pH, suggesting that pH is the best soil related predictor of decomposition parameters. The discussion is focused on the ecological significance of decomposition parameters in relation to the quality of soil humus and soil physico-chemical characteristics.

Agronomic and environmental aspects of utilization of organic residues in soils of the Andean-Patagonian Region

Patterns of N mineralization and P release were determined in two characteristic soils of the Andean-Patagonian Region (Andisol) and the transitional zone to the steppe (xeric Mollisol) amended with fish residues and biosolids. Residues were applied to the soils at rates of 10–20 g kg-1 and incubated for 112 d under controlled temperature and soil moisture conditions using a non-leaching procedure. Nitrogen mineralized from the total added N depended mainly on the type of residues, while P release depended firstly on the soil type, and secondly on the residue type. Fish residues displayed a potential as slow-release N fertilizers, while biosolids showed a marked initial flush of mineralized N. Due to the high P content, fish residues might exert adverse environmental and agronomic effects on the xeric Mollisol when applied at the rates to meet crop N requirements. In the Andisol with a high P retention capacity, the applied rates would cover both Nand P crop requirements. Biosolids were unable to supply an adequate amount of available P in the Andisol, possibly due to the addition of Al-sulfate and, consequently, the formation of Al-P species with low solubility.