Use of the EPR technique to determine thermal stability of some humified organic substances found in soil organic-mineral fractions

In this work, using the EPR spectroscopy, we analysed the thermal stability of some organic-mineral compounds found in a Gleysoil from Rio Janeiro. It was observed a complete disappearance of the EPR signal around 600 °C for the < 2 µm fraction and a residual EPR signal of semiquinone free radical for the 2-20 µm and 20-53 µm fractions at the same temperature. Also, the experiments showed that the 2-20 µm fraction had a larger concentration of semiquinone free radical per g of carbon and a smaller line width indicated a larger humification of this fraction. This is an evidence that the soil organic matter of this fraction (2-20 µm) is more stable than the other ones.

SOIL COVER AND CHEMICAL AND PHYSICAL ATTRIBUTES IN OXISOL IN THE ATLANTIC FOREST BIOME

ABSTRACT The objective of this study was to evaluate the chemical and physical attributes of different soil cover in a Oxisol with a strong wavy relief in the Atlantic Forest Biome, in which were selected three watersheds, employed with grazing (watershed P), forest (watershed M) and coffee (watershed C). Deformed and not deformed samples were collected in three depths for physical and chemical characterization. The chemical characteristics of soil in different watershed studies presented low levels of fertility. It was observed an elevation of pH in the soil and contents of Ca2+ and Mg2+ in the watersheds P and C in relation to the watershed M. Due to deforestation and the establishment of agriculture and livestock, there was a decrease in the contents of soil organic matter in the watershed P and C, not altering the physical characteristics of the soil in the watershed P. The implementation of coffee plantation is causing a reduction in the soil quality of watershed C in comparison to the watershed P and M, therefore indicating a need to adequate soil management in this area.

Management zones definition using soil chemical and physical attributes in a soybean area

Several equipments and methodologies have been developed to make available precision agriculture, especially considering the high cost of its implantation and sampling. An interesting possibility is to define management zones aim at dividing producing areas in smaller management zones that could be treated differently, serving as a source of recommendation and analysis. Thus, this trial used physical and chemical properties of soil and yield aiming at the generation of management zones in order to identify whether they can be used as recommendation and analysis. Management zones were generated by the Fuzzy C-Means algorithm and their evaluation was performed by calculating the reduction of variance and performing means tests. The division of the area into two management zones was considered appropriate for the present distinct averages of most soil properties and yield. The used methodology allowed the generation of management zones that can serve as source of recommendation and soil analysis; despite the relative efficiency has shown a reduced variance for all attributes in divisions in the three sub-regions, the ANOVA did not show significative differences among the management zones.

Physical attributes of a pasture soil in southeast Goiás determined by geostatistics

ABSTRACT This study aimed to evaluate the spatial dependence of physical attributes in a soil cultivated with Brachiaria grass. A 12-m regular sampling grid was established within an area of 3.500 m2. Thirty-five soil samples were collected at 0-30 cm depth for particle density, bulk density, texture and total porosity analysis. These data were evaluated using statistical methods of indicator kriging and the GS+ software. The GS+ software was used to develop three-dimensional maps and evaluate semivariograms. The spatial dependence was evaluated using experimental semivariograms. The analyzed attributes indicated the occurrence of spatial dependence when fit to the exponential model. Areas with higher porosity occurred in the regions with lower bulk densities and higher particle densities.

Influence of heat treatment on the sensory and physical characteristics and carbohydrate fractions of french-fried potatoes (Solanum tuberosum L.)

AbstractThe aim of this study was to analyze the impact that heat treatment with salts and freezing processes on the sensory, instrumental, and physico-chemical characteristics of fried potatoes of the Monalisa cultivar. The potatoes were blanched in distilled water (P); sodium chloride solution (B1); calcium chloride solution (B2), and a solution with both of these salts (B3). They were then pre-cooked and frozen for 24 hours and for 30 days. After frying, sensory characteristics were analyzed (color, texture, flavor, oiliness), along with overall preference and instrumental determinations of texture, color, and oil content. Further tests were conducted on the sample with the best results in the sensory analysis (B1), along with sample P as a control, to determine granule microstructure, carbohydrate fractions, glycemic index, and glycemic load. Blanching B3, despite reducing oil absorption and providing less oiliness, obtained lesser overall preference. Freezing for 30 days increased the lightness, except for when sodium chloride was used, which intensified the color yellow. The use of sodium chloride did not interfere with the type of starch granules, nor with the formation of resistant starch; however, longer freezing time reduced the glycemic index and concentrated the dietary fiber content. All samples exhibited low glycemic index and moderate glycemic loads.

Composition and stability of organic matter fractions in soils under different land use regimes

Soil organic matter (SOM) vitally impacts all soil functions and plays a key role in the global carbon (C) cycle. More than 70% of the terrestric C stocks that participate in the active C cycle are stored in the soil. Therefore, quantitative knowledge of the rates of C incorporation into SOM fractions of different residence time is crucial to understand and predict the sequestration and stabilization of soil organic carbon (SOC). Consequently, there is a need of fractionation procedures that are capable of isolating functionally SOM fractions, i.e. fractions that are defined by their stability. The literature generally refers to three main mechanisms of SOM stabilization: protection of SOM from decomposition by (i) its structural composition, i.e. recalcitrance, (ii) spatial inaccessibility and/or (iii) interaction with soil minerals and metal ions. One of the difficulties in developing fractionation procedures for the isolation of functional SOM fractions is the marked heterogeneity of the soil environment with its various stabilization mechanisms – often several mechanisms operating simultaneously – in soils and soil horizons of different texture and mineralogy. The overall objective of the present thesis was to evaluate present fractionation techniques and to get a better understanding of the factors of SOM sequestration and stabilization. The first part of this study is attended to the structural composition of SOM. Using 13C cross-polarization magic-angle spinning (CPMAS) nuclear magnetic resonance (NMR) spectroscopy, (i) the effect of land use on SOM composition was investigated and (ii) examined whether SOM composition contributes to the different stability of SOM in density and aggregate fractions. The second part of the present work deals with the mineral-associated SOM fraction. The aim was (iii) to evaluate the suitability of chemical fractionation procedures used in the literature for the isolation of stable SOM pools (stepwise hydrolysis, treatments using oxidizing agents like Na2S2O8, H2O2, and NaOCl as well as demineralization of the residue obtained by the NaOCl treatment using HF (NaOCl+HF)) by pool sizes, 13C and 14C data. Further, (iv) the isolated SOM fractions were compared to the inert organic matter (IOM) pool obtained for the investigated soils using the Rothamsted Carbon Model and isotope data in order to see whether the tested chemical fractionation methods produce SOM fractions capable to represent this pool. Besides chemical fractionation, (v) the suitability of thermal oxidation at different temperatures for obtaining stable SOC pools was evaluated. Finally, (vi) the short-term aggregate dynamics and the factors that impact macroaggregate formation and C stabilization were investigated by means of an incubation study using treatments with and without application of 15N labeled maize straw of different degradability (leaves and coarse roots). All treatments were conducted with and without the addition of fungicide. Two study sites with different soil properties and land managements were chosen for these investigations. The first one, located at Rotthalmünster, is a Stagnic Luvisol (silty loam) under different land use regimes. The Ah horizons of a spruce forest and continuous grassland and the Ap and E horizons of two plots with arable crops (continuous maize and wheat cropping) were examined. The soil of the second study site, located at Halle, is a Haplic Phaeozem (loamy sand) where the Ap horizons of two plots with arable crops (continuous maize and rye cropping) were investigated. Both study sites had a C3-/C4-vegetational change on the maize plot for the purpose of tracing the incorporation of the younger, maize-derived C into different SOM fractions and the calculation of apparent C turnover times of these. The Halle site is located near a train station and industrial areas, which caused a contamination with high amounts of fossil C. The investigation of aggregate and density fractions by 13C CPMAS NMR spectroscopy revealed that density fractionation isolated SOM fractions of different composition. The consumption of a considerable part (10–20%) of the easily available O-alkyl-C and the selective preservation of the more recalcitrant alkyl-C when passing from litter to the different particulate organic matter (POM) fractions suggest that density fractionation was able to isolate SOM fractions with different degrees of decomposition. The spectra of the aggregate fractions resembled those of the mineral-associated SOM fraction obtained by density fractionation and no considerable differences were observed between aggregate size classes. Comparison of plant litter, density and aggregate size fractions from soil under different land use showed that the type of land use markedly influenced the composition of SOM. While SOM of the acid forest soil was characterized by a large content (> 50%) of POM, which contained high amounts of spruce-litter derived alkyl-C, the organic matter in the biologically more active grassland and arable soils was dominated by mineral-associated SOM (> 95%). This SOM fraction comprised greater proportions of aryl- and carbonyl-C and is considered to contain a higher amount of microbially-derived organic substances. Land use can alter both, structure and stability of SOM fractions. All applied chemical treatments induced considerable SOC losses (> 70–95% of mineral-associated SOM) in the investigated soils. The proportion of residual C after chemical fractionation was largest in the arable Ap and E horizons and increased with decreasing C content in the initial SOC after stepwise hydrolysis as well as after the oxidative treatments with H2O2 and Na2S2O8. This can be expected for a functional stable pool of SOM, because it is assumed that the more easily available part of SOC is consumed first if C inputs decrease. All chemical treatments led to a preferential loss of the younger, maize-derived SOC, but this was most pronounced after the treatments with Na2S2O8 and H2O2. After all chemical fractionations, the mean 14C ages of SOC were higher than in the mineral-associated SOM fraction for both study sites and increased in the order: NaOCl < NaOCl+HF ≤ stepwise hydrolysis << H2O2 ≈ Na2S2O8. The results suggest that all treatments were capable of isolating a more stable SOM fraction, but the treatments with H2O2 and Na2S2O8 were the most efficient ones. However, none of the chemical fractionation methods was able to fit the IOM pool calculated using the Rothamsted Carbon Model and isotope data. In the evaluation of thermal oxidation for obtaining stable C fractions, SOC losses increased with temperature from 24–48% (200°C) to 100% (500°C). In the Halle maize Ap horizon, losses of the young, maize-derived C were considerably higher than losses of the older C3-derived C, leading to an increase in the apparent C turnover time from 220 years in mineral-associated SOC to 1158 years after thermal oxidation at 300°C. Most likely, the preferential loss of maize-derived C in the Halle soil was caused by the presence of the high amounts of fossil C mentioned above, which make up a relatively large thermally stable C3-C pool in this soil. This agrees with lower overall SOC losses for the Halle Ap horizon compared to the Rotthalmünster Ap horizon. In the Rotthalmünster soil only slightly more maize-derived than C3-derived SOC was removed by thermal oxidation. Apparent C turnover times increased slightly from 58 years in mineral-associated SOC to 77 years after thermal oxidation at 300°C in the Rotthalmünster Ap and from 151 to 247 years in the Rotthalmünster E horizon. This led to the conclusion that thermal oxidation of SOM was not capable of isolating SOM fractions of considerably higher stability. The incubation experiment showed that macroaggregates develop rapidly after the addition of easily available plant residues. Within the first four weeks of incubation, the maximum aggregation was reached in all treatments without addition of fungicide. The formation of water-stable macroaggregates was related to the size of the microbial biomass pool and its activity. Furthermore, fungi were found to be crucial for the development of soil macroaggregates as the formation of water-stable macroaggregates was significantly delayed in the fungicide treated soils. The C concentration in the obtained aggregate fractions decreased with decreasing aggregate size class, which is in line with the aggregate hierarchy postulated by several authors for soils with SOM as the major binding agent. Macroaggregation involved incorporation of large amounts maize-derived organic matter, but macroaggregates did not play the most important role in the stabilization of maize-derived SOM, because of their relatively low amount (less than 10% of the soil mass). Furthermore, the maize-derived organic matter was quickly incorporated into all aggregate size classes. The microaggregate fraction stored the largest quantities of maize-derived C and N – up to 70% of the residual maize-C and -N were stored in this fraction.

Exploring the enzymatic landscape: distribution and kinetics of hydrolytic enzymes in soil particle-size fractions

The location of extracellular enzymes within the soil architecture and their association with the various soil components affects their catalytic potential. A soil fractionation study was carried out to investigate: (a) the distribution of a range of hydrolytic enzymes involved in C, N and P transformations, (b) the effect of the location on their respective kinetics, (c) the effect of long-term N fertilizer management on enzyme distribution and kinetic parameters. Soil (silty clay loam) from grassland which had received 0 or 200 kg N ha(-1) yr(-1) was fractionated, and four particle-size fractions (> 200, 200-63, 63-2 and 0. 1-2 mum) were obtained by a combination of wet-sieving and centrifugation, after low-energy ultrasonication. All fractions were assayed for four carbohydrases (beta-cellobiohydrolase, N-acetyl-beta-glucosammidase, beta-glucosidase and beta-xylosidase), acid phosphatase and leucine-aminopeptidase using a microplate fluorimetric assay based on MUB-substrates. Enzyme kinetics (V-max and K-m) were estimated in three particle-size fractions and the unfractionated soil. The results showed that not all particle-size fractions were equally enzymatically active and that the distribution of enzymes between fractions depended on the enzyme. Carbohydrases predominated in the coarser fractions while phosphatase and leucine-aminopeptidase were predominant in the clay-size fraction. The Michaelis constant (K.) varied among fractions, indicating that the association of the same enzyme with different particle-size fractions affected its substrate affinity. The same values of Km were found in the same fractions from the soil under two contrasting fertilizer management regimes, indicating that the Michaelis constant was unaffected by soil changes caused by N fertilizer management. (C) 2004 Elsevier Ltd. All rights reserved.

Plant roots release phospholipid surfactants that modify the physical and chemical properties of soil

Plant root mucilages contain powerful surfactants that will alter the interaction of soil solids with water and ions, and the rates of microbial processes. The lipid composition of maize, lupin and wheat root mucilages was analysed by thin layer chromatography and gas chromatography-mass spectrometry. A commercially available phosphatidylcholine (lecithin), chemically similar to the phospholipid surfactants identified in the mucilages, was then used to evaluate its effects on selected soil properties. The lipids found in the mucilages were principally phosphatidylcholines, composed mainly of saturated fatty acids, in contrast to the lipids extracted from root tissues. In soil at low tension, lecithin reduced the water content at any particular tension by as much as 10 and 50% in soil and acid-washed sand, respectively. Lecithin decreased the amount of phosphate adsorption in soil and increased the phosphate concentration in solution by 10%. The surfactant also reduced net rates of ammonium consumption and nitrate production in soil. These experiments provide the first evidence we are aware of that plant-released surfactants will significantly modify the biophysical environment of the rhizosphere.

Carbon fractions associated with silt-size particles in surface and subsurface soil horizons

Information on the distribution and behavior of C fractions in soil particle sizes is crucial for understanding C dynamics in soil. At present little is known about the behavior of the C associated with silt-size particles. We quantified the concentrations, distribution, and enrichment of total C (TC), readily oxidizable C (ROC), hotwater- extractable C (HWC), and cold-water-extractable C (CWC) fractions in coarse (63–20-mm), medium (20–6.3-mm), and fine (6.3–2-mm) silt-size subfractions and in coarse (2000–250 mm) and fine (250–63 mm) sand and clay (<2-mm) soil fractions isolated from bulk soil (<2 mm), and 2- to 4-mm aggregate-size fraction of surface (0–25 cm) and subsurface (25–55 cm) soils under different land uses. All measured C fractions varied significantly across all soil particle-size fractions. The highest C concentrations were associated with the <20-mm soil fractions and peaked in the medium (20–6.3-mm) and fine (6.3–2-mm) silt subfractions in most treatments. Carbon enrichment ratios (ERC) revealed the dual behavior of the C fractions associated with the medium silt-size fraction, demonstrating the simultaneous enrichment of TC and ROC, and the depletion of HWC and CWC fractions. The medium silt (20–6.3-mm) subfraction was identified in this study as a zone where the associated C fractions exhibit transitory qualities. Our results show that investigating subfractions within the silt-size particle fraction provides better understanding of the behavior of C fractions in this soil fraction.

Organic matter fractions and soil fertility under the influence of liming, vermicompost and cattle manure

Os efeitos do vermicomposto de esterco de curral associado à calagem em atributos da fertilidade do solo foram avaliados através de experimento em vasos empregando um Latossolo Vermelho, distrófico, textura média. Cinco doses do vermicomposto (equivalentes a 0; 28; 42; 56 e 70 t ha-1, peso seco) e cinco doses de calcário (visando elevar a saturação por bases a: 20; 30; 40; 50 e 60%) foram combinadas em esquema fatorial, sendo as amostras de solo incubadas por 180 dias. Para comparação entre o vermicomposto e o esterco de curral, amostras do mesmo solo receberam o equivalente a 70 t ha-1 do esterco de curral que originou o vermicomposto e as cinco doses de calcário listadas anteriormente. Através do cálculo do Índice de Eficiência Agronômica, foi verificado que o potencial de fornecimento de K e de Mg pelo esterco é maior do que o do vermicomposto, e que o de P, é semelhante. O vermicomposto aumentou os teores de Ca2+ e de matéria orgânica (MO), os valores de pH em CaCl2 e a CTC a pH 7. Com o aumento das doses de vermicomposto houve diminuição do C-ácidos húmicos e aumento do C-humina e com a calagem o C-total não aumentou mas houve diminuição do C-ácidos húmicos.

Soil uses in the sugarcane fallow period to improve chemical and physical properties of two latosols (oxisols)

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Nutrient recycling and physical indicators of an alley cropping system in a sandy loam soil in the pre-Amazon region of Brazil

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Spatial variability of the physical and mineralogical properties of the soil from the areas with variation in landscape shapes

Este trabalho teve como objetivo avaliar a influência das formas do relevo na variabilidade espacial de atributos físicos e suas relações com a mineralogia da argila de um Latossolo Vermelho eutroférrico, utilizando a técnica da geoestatística. Os solos foram amostrados nos pontos de cruzamento de uma malha, com intervalos regulares de 10 m, nas profundidades de 0,0-0,2 m, 0,2-0,4 m e 0,4-0,6 m para os atributos físicos e 0,6-0,8 m para os atributos mineralógicos. Os valores médios para a densidade do solo e resistência do solo à penetração são maiores no compartimento I onde a relação Ct/Ct+Gb é relativamente maior, indicando a presença de maior teor de caulinita. No compartimento II a condutividade hidráulica e a macroporsidade são maiores, influenciados provavelmente pelo predomínio da gibbsita. Portanto, conclui-se que a identificação das pedoformas é muito eficiente para compreender a variabilidade espacial de propriedades do solo. Sendo que, as variações na forma da paisagem promovem variabilidade espacial diferenciada das propriedades físicas e mineralógicas do solo.

Soil microbial biomass and organic matter fractions during transition from conventional to organic farming systems

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Heavy metals availability and fractions in soil amended with biosolid composts

The heavy metals when linked to organic matter have a behavior in the soil that is still little known. This study aimed to evaluate the effect of sewage-sludge-based composts when incorporated in the soil, in relation to heavy metals availability. Five composts were incorporated using sugar-cane bagasse, sewage sludge and cattle manure in the respective proportions: 75-0-25, 75-12.5-12.5, 75-25-0, 50-50-0 and 0-100-0 (composts with 0, 12.5, 25, 50 and 100% sewage sludge). The experiment consisted of 6 treatments (5 composts and a control with mineral fertilization) in randomized blocks with a split-plot design. The control and the treatment of 0% sewage sludge received inorganic nitrogen (N). All the treatments received the same amount of N (8.33 g) K (5.80 g) and K (8.11 g) per pot. Tomato plants were cultivated in 24.0 L pots in a greenhouse in Jaboticabal, SP, Brazil. The concentrations of heavy metals were determined in the soil samples at day 0 after compost incorporation. The higher the sewage sludge doses, the higher heavy metal contents in the soil. Among extractants, Melhlich-1 extracted the highest amount of heavy metals, while DTPA extracted the lowest one. The residual fraction presented the highest heavy metal content, followed by Fe oxides crystalline and amorphous to Cu, Cr and Mn, and Mn oxides, and Fe amorphous to Zn, indicating strong associations to oxides and clays. There were significant positive correlations between Mn contents in the plant and Mn linked to Fe oxide amorphous and crystalline.