Rhodic Ferralsol Research Articles

Chemical migration during soil water retention curve evaluation

Wetting and drying (W-D) cycles can induce important elemental migrations in soils. The main purpose of this work was to study the possible existence of soil chemical elemental migrations in samples submitted to repeated W-D cycles during evaluations of soil water retention curve (SWRC). The experimental measurements were carried out by Atomic Absorption Spectrometry (AAS) for Ca(2+), Mg(2+) and K(+) on samples of three different Brazilian tropical soils (Geric Ferralsol, Eutric Nitosol and Rhodic Ferralsol). Results demonstrate an increase in the electrical conductivity of the water extracted from the samples and significant losses of Ca(2+), Mg(2+) and K(+) during the applications of up to nine W-D cycles. It was also observed differences in SWRC for all soils when samples submitted to the application of several W-D cycles were compared with samples not submitted to it. These differences occurred at the region of both structural and textural pores. A possible explanation for these results could be the soil chemical migration during the sequences of W-D cycles, which can affect the soil structure development.

Biochemical and physiological responses of sugarcane cultivars to soil water deficiencies

For sugarcane (Saccharum spp.) crops, the effects of an environmental stress, especially water deficiency, may cause severe productivity reduction, inferring negatively in the sugarcane industry. The tolerance of two sugarcane cultivars to a lack of water was made by analyzing the levels of the osmoprotectors, trehalose and free proline, and the biometrical variables of their initial growth. Biochemical and physiological responses of the cultivars, when subjected to water stress, were assayed to determine how these plants tolerate drought. The study was conducted in an acclimatized greenhouse (29.7 ± 4.3oC and 75.0 ± 10.1% relative humidity) during 100 days and was divided into random blocks using a factorial 2 × 3 × 2 design (sugarcane cultivars × water availability × time periods) with four replicates. Forty days after germination, sugarcane was planted in pots (12 dm³) containing topsoil material taken from a medium textured Rhodic Ferralsol, submitted to three levels of water availability (WAS): 55% (control), 40% (moderate stress) and 25% (severe stress), for 60 days. The effect of the WAS on the accumulation of trehalose and free proline was detected in both cultivars, although it was found to be more distinctive for the cv. IAC91-5155. Trehalose and free proline are biochemical and physiological indicators of water deficiency. The cv. IAC91-5155 had altered growth and allocation of biomass when subjected to severe water stress conditions. The univariate and the multivariate analysis of the biochemical and physiological responses, presented by the IAC91-5155 cultivar, indicate relative tolerance to drought conditions.

Lixiviação de nutrientes em solo cultivado com aplicação de água residuária de suinocultura

Objetivou-se neste trabalho avaliar os impactos do percolado em lisímetros de drenagem com a aplicação de diferentes taxas de água residuária de suinocultura (ARS) durante o ciclo da cultura da soja. Conduziu-se o experimento no Núcleo Experimental de Engenharia Agrícola da UNIOESTE, em solo foi classificado como Latossolo Vermelho distroférrico. A área dispunha 24 lisímetros de drenagem, na qual se semeou a cultura da soja, cultivar CD 214. Porém, sete dias antes da semeadura, em única aplicação foram aplicadas ao solo quatro taxas de ARS (0, 100, 200 e 300 m³ ha-1) sete dias antes da semeadura, em uma única aplicação, combinadas com duas adubações na semeadura (com adição e sem adição da adubação recomendada na semeadura) e três repetições por tratamento. Foram realizadas três coletas do percolado em cada parcela experimental, a primeira aos 40 dias após a semeadura (DAS), a segunda aos 72 DAS e a terceira no final do ciclo da cultura (117 DAS). Avalioram-se pH, cálcio, magnésio, potássio, fósforo e nitrogênio total. Com base nos resultados observou-se que os valores de pH e Mg no percolado não sofreram influência pela aplicação de ARS e adubação. As concentrações de K+, P e Ca+2 no percolado foram maiores para taxas mais elevadas de ARS.

Characterization of a Brazilian clayey soil submitted to conventional and no-tillage management practices using pore size distribution analysis

In this paper is presented the use of soil water retention curves (SWRC) to investigate modifications in pore size distribution (PSD) of a Rhodic Ferralsol submitted to two different long term management practices: no-tillage (NT) and conventional tillage (CT). Soils from both treatments were investigated in 3 different depths, 0–10, 10–20, and 20–30cm and matric potential values that varied from 0 to −780kPa. The obtained results showed trimodal PSDs for both treatments, indicating well structured soils. The obtained results suggested that soil under conventional tillage CT and no-tillage NT: (a) first, have modified their structure depending on the treatment they were submitted; (b) second, have their macroporosity reduced to larger depths; and (c) third, have their microporosity largely altered, mainly at the surface, presenting the soil under NT a large microporosity for all investigated depths.

Adsorção de fósforo em frações argila na presença de ácido fúlvico

Os ácidos orgânicos podem ser adsorvidos aos coloides do solo, favorecendo maior disponibilidade de P às plantas. Por meio de isotermas, avaliou-se a influência de ácido fúlvico (AF) sobre a adsorção de P na fração argila de dois Latossolos Vermelhos (LVdf e LVd), caulinita natural pouco cristalizada (KGa2), goethita (Gt) e hematita (Hm) sintéticas. As isotermas de adsorção de P ajustadas pelo modelo de Langmuir na presença de AF foram adequadas somente para a região de baixa concentração de P. De maneira geral, a presença de AF incubado nas frações argila estudadas foi capaz de reduzir a adsorção de P. Na fração argila do LVdf, a adsorção de P em baixas e altas concentrações desse nutriente teve pequena influência da sequência de incubação de P com AF, enquanto para a fração argila do LVd as sequências de incubação com P e AF influenciaram a adsorção de P. A redução da adsorção de P sobre a fração argila da KGa2 em baixas concentrações de P nas isotermas não dependeu da sequência de incubação de P e AF, e sim da presença do AF. Na região de altas concentrações de P, a sequência de incubação de P e AF influenciou a adsorção desse elemento. A adsorção de P sobre Gt foi dependente da sequência de incubação com AF, e a incubação prévia do AF promoveu redução da adsorção de P. A sequência de incubação do P e AF na Hm influenciou a adsorção de P quando em baixas e altas concentrações nas isotermas. Os menores valores de adsorção de P ocorreram com a incubação de P juntamente ao AF ou incubação de AF precedida da do P.

Availability of soil water under tillage systems, mulch management and citrus rootstocks

The increased availability of soil water is important for the management of non-irrigated orange orchards. The objective of this study was to evaluate the availability of soil water in a Haplorthox (Rhodic Ferralsol) under different tillage systems used for orchard plantation, mulch management and rootstocks in a "Pêra" orange orchard in northwest Paraná, Brazil. An experiment in a split-split-plot design was established in 2002, in an area cultivated with Brachiaria brizantha grass in which three tillage systems (no tillage, conventional tillage and strip-tillage) were used for orchard plantation. This grass was mowed twice a year between the rows, representing two mulch managements in the split plots (no mulching and mulching in the plant rows). The split-split-plots were represented by two rootstocks ("Rangpur" lime and "Cleopatra" mandarin). The soil water content in the plant rows was evaluated in the 0-20 cm layer in 2007 and at 0-20 and 20-40 cm in 2008-2009. The effect of soil tillage systems prior to implantation of orange orchards on soil water availability was less pronounced than mulching and the rootstocks. The soil water availability was lower when "Pêra" orange trees were grafted on "Cleopatra" mandarin than on "Rangpur" lime rootstocks. Mulching had a positive influence on soil water availability in the sandy surface layer (0-20 cm) and sandy clay loam subsurface (20-40 cm) of the soil in the spring. The production of B. brizantha between the rows and residue disposal in the plant rows as mulch increased water availability to the "Pêra" orange trees.

Área superficial específica, porosidade da fração argila e adsorção de fósforo em dois latossolos vermelhos

A porosidade da fração argila é muito importante para entendimento dos fenômenos físico-químicos que estão relacionados com a área superficial específica das partículas sólidas. Por meio de isotermas de adsorção e dessorção com N2, avaliaram-se a área superficial específica (S BET) e a porosidade das frações argila de Latossolos Vermelhos do Estado de Mato Grosso do Sul, sendo um distroférrico (LVdf) e outro distrófico (LVd), além de caulinita natural (KGa2), goethita (Gt) e hematita (Hm) sintéticas. Resultados referentes à S BET e à porosidade das partículas foram relacionados à adsorção máxima de P (Pmáx) determinada pela isoterma de Langmuir. A classe de poros predominante nas frações argila avaliadas foi de mesoporos. As frações argila extraídas dos solos e KGa2 adsorveram quantidades semelhantes de P por unidade de área, mas diferentes das quantidades de P adsorvido por Gt e Hm. Tal diferença, possivelmente, deu-se em função da quantidade e distribuição dos grupamentos OH em superfície, bem como imperfeições superficiais dos materiais. Os óxidos de Fe e de Al e outros materiais amorfos das frações argila extraídas dos solos foram mais importantes que a caulinita para a adsorção de P. A caulinita, embora sendo o filossilicato de maior representatividade nas frações argila de LVDf e LVD, teve menor importância sobre a adsorção de P.

Impacts of limestone and nitrogen top dressing application on the potassium content in the soil profile and marandu-grass leaf concentration

The objective of this experiment was to evaluate the effects of nitrogen doses (0, 100, 200, 300, and 400 kg ha-1 year-1), with or without dolomitic lime covering application, on the potassium (K) soil content at depths varying form 0 to 5, 5 to 10, and 10 to 20 cm, and the potassium concentration in the plant. The experiment was carried out in a rhodic ferralsol with a slightly rolling relief, in a 5 × 2 factorial arrangement, in a complete randomized block design, with four replications. Nitrogenated fertilization caused a linear increase in the potassium concentration in the plant and also in the mineral content in the 0-5 cm soil layer. An effect of competitive inhibition occurred between the potassium and calcium absorption, and potassium and magnesium absorption. Although a significant fraction of potassium returned to the soil surface layer through the forage residue due to the increase in dry matter production caused by nitrogenated fertilization, the increase in the potassium concentration in the plant due to the doses of nitrogen demonstrated the importance of considering the potassium supply to the plant, when the forage mass is intensified through nitrogenated fertilization.

The impact of soil management on aggregation, carbon stabilization and carbon loss as CO 2 in the surface layer of a Rhodic Ferralsol in Southern Brazil

Soil aggregation and organic carbon accumulation are two intrinsically linked phenomena. Soils under natural vegetation and conservation tillage systems generally have higher aggregation indices and total organic carbon (TOC) stocks in the surface layers than soils under conventional management (ploughing). From the point of view of the emission of carbon dioxide (CO 2), C stabilization and loss in the surface layer is relevant. The objective of this study was to investigate the effect of no-tillage (NT) and conventional tillage (CT) on TOC stabilization and loss through soil aggregation in the topsoil. Soil aggregation, TOC stocks, and fluxes of CO 2 of samples from a Rhodic Ferralsol under NT and CT in a long-term field experiment in Southern Brazil were measured. A natural forest site was also evaluated as reference to the management sites. Emissions of CO 2 were measured in laboratory incubation experiment on bulk soil samples and on soil aggregate size fractions, previously separated by dry sieving, in intact and destroyed (crushed to <0.250 mm) state. The soil under NT had larger aggregates and larger proportion of the soil in greater aggregate size classes than CT. Total organic carbon stocks were higher under NT both in bulk soil samples and macroaggregates than under CT. Under laboratory conditions the bulk soil samples from NT showed higher emission rates of CO 2 (CO 2BS = 18.3 kg C ha −1 h −1) than from CT (CO 2BS = 2.3 kg C ha −1 h −1) due to the overall higher TOC stocks. The TOC that was lost by CO 2 emission due to the oxidation of readily decomposable macroaggregate-protected SOM in NT (ΣΔCO 2 = 79.4 kg C ha −1 h −1) was, however, also higher than under CT (CT: ΣΔCO 2 = 29.1 kg C ha −1 h −1). The TOC stabilized by macroaggregation in NT was also more than the TOC lost by CO 2 emission from the bulk soil (ΣΔCO 2-CO 2BS = 61.1 kg C ha −1 h −1), and the difference between these two was higher under NT than under CT (ΣΔCO 2-CO 2BS = 26.8 kg C ha −1 h −1), showing that NT in fact accumulates more TOC in the soil by protecting it within the macroaggregates. The natural forest had higher TOC stock and emission rates than the tilled soils, however it also stabilized more TOC. Thus, no-tillage in its effect on carbon stabilization, is between the natural ecosystem and CT, representing a soil management system that seems to be an efficient on the way path to the recuperation of soil after conventional management systems.

Pore system changes of damaged Brazilian oxisols and nitosols induced by wet-dry cycles as seen in 2-D micromorphologic image analysis

Soil pore structure characterization using 2-D image analysis constitutes a simple method to obtain essential information related to soil porosity and pore size distribution (PSD). Such information is important to infer on soil quality, which is related to soil structure and transport processes inside the soil. Most of the time soils are submitted to wetting and drying cycles (W-D), which can cause important changes in soils with damaged structures. This report uses 2-D image analysis to evaluate possible modifications induced by W-D cycles on the structure of damaged soil samples. Samples of three tropical soils (Geric Ferralsol, GF; Eutric Nitosol, EN; and Rhodic Ferralsol, RF) were submitted to three treatments: 0WD, the control treatment in which samples were not submitted to any W-D cycle; 3WD and 9WD with samples submitted to 3 and 9 consecutive W-D cycles, respectively. It was observed that W-D cycles produced significant changes in large irregular pores of the GF and RF soils, and in rounded pores of the EN soil. Nevertheless, important changes in smaller pores (35, 75, and 150 µm) were also observed for all soils. As an overall consideration, it can be said that the use of image analysis helped to explain important changes in soil pore systems (shape, number, and size distribution) as consequence of W-D cycles.

Effect of ionic strength on adsorption of As(III) and As(V) on variable charge soils

The study was to investigate the adsorption behavior of arsenite (As(III)) and arsenate (As(V)) on two variable charge soils, i.e., Haplic Acrisol and Rhodic Ferralsol at different ionic strengths and pH with batch methods. Results indicated that the amount of As(III) adsorbed by these two soils increased with increasing solution pH, whereas it decreased with increasing ionic strength under the acidic condition. This suggested that As(III) was mainly adsorbed on soil positive charge sites through electrostatic attraction under the acidic condition. Moreover, intersects of As(V) adsorption-pH curves at different ionic strengths (a characteristic pH) are obtained for both soils. It was noted that above this pH, the adsorption of As(V) was increased with increasing ionic strength, whereas below it the reverse trend was true. Precisely the intersect pH was 3.6 for Haplic Acrisol and 4.5 for Rhodic Ferralsol, which was near the values of PZSE (soil point of zero salt effect) of these soils. The effects of ionic strength and pH on arsenate adsorption by these soils were interpreted by the adsorption model. The results of zeta potential suggested that the potential in adsorption plane becomes less negative with increasing ionic strength above soil PZSE and decreases with increasing ionic strength below soil PZSE. These results further supported the hypothesis of the adsorption model that the potential in the adsorption plane changes with ionic strength with an opposite trend to surface charge of the soils. Therefore, the change of the potential in the adsorption plane was mainly responsible for the change of arsenate adsorption induced by ionic strength on variable charge soils.

Carbon stocks of a Rhodic Ferralsol under no-tillage in Southern Brazil: spatial variability at a farm scale

The objective of this study was to determine, at a farm level, the spatial variability of organic carbon stock (CS) at different depths on a field of 1 soil type in long-term (13-year) crop production under no-tillage. The crop rotation comprised soybean [Glycine max (L.) Merr.] alternating with maize (Zea mays L.) in the summer season. For the winter season, wheat (Triticum aestivum L.) was cropped in rotation with black oat (Avena sativa L.), a cover crop. The 12.5-ha field was sampled at a density of 6.25 samples/ha. Within the coarse grid, 2 dense grids with 20-, 10-, and 5-m spacing were established. Soil samples were collected at all grid nodes and analysed for soil organic carbon and bulk density. The CS at 0–0.05, 0.05–0.10, and 0.10–0.20 m was corrected for equal soil mass. Geostatistics was used for the estimation of spatial distribution of CS at 3 soil depths. We found that CS variation was low to medium (CV 6.7–19.4%). The variograms of CS at all depths were best fitted by spherical models and showed ranges of 120 m, except at 0–0.05 m (range 109 m). At 0–0.20 m depth, CS was 15.2–24.5 t/ha (CV 8.2%, range 120 m). The use of geostatistics reveals a powerful tool for the spatial estimation of CS at depth of a Rhodic Ferralsol under no-tillage, and demonstrated CS variation on a 12.5-ha area, even though soil and crop management were the same for &gt;10 years.

Qualidade física do solo em pastagem adubada e sob pastejo contínuo

O objetivo deste trabalho foi avaliar a qualidade física do solo em pastagens submetidas ao pastejo contínuo. As pastagens foram formadas com capim-coastcross (Cynodon dactylon) consorciado ou não com a leguminosa amendoim forrageiro (Arachis pintoi). A pastagem consorciada recebeu os tratamentos de 0, 100 e 200 kg ha-1 de nitrogênio (N) por ano e a pastagem sem consórcio recebeu 200 kg ha-1 de N por ano, no total de quatro tratamentos. O experimento foi implantado em 2002, em Latossolo Vermelho distrófico, em Paranavaí, PR, em delineamento de blocos ao acaso, com duas repetições. A taxa de lotação animal foi controlada em função da oferta de forragem, entre 2002 e 2007. Em março e novembro de 2007 foram coletadas amostras indeformadas de solo, nas camadas 0-75 e 75-150 mm de profundidade, para determinação da densidade, porosidade e capacidade de armazenamento de ar e de água do solo. O pastejo em sistema de lotação contínua, com controle da taxa de lotação animal em função da produção de forragem, não comprometeu a qualidade física do solo. A capacidade de armazenamento de água do solo é um indicador sensível para se avaliarem os efeitos da intensificação da utilização da pastagem sobre a qualidade física do solo.

Improved estimation of biological nitrogen fixation of soybean cultivars (Glycine max L. Merril) using 15N natural abundance technique

Biological nitrogen fixation (BNF) of 17 soybean cultivars was comparatively estimated by the δ15N natural abundance technique using two non-nodulation soybeans (Clay and Chippewa) as reference plants. A field study was established on the experimental farm of the University of Abomey-Calavi, Benin on a typical “terre de barre” soil classified by Food and Agriculture Organization-United Nations Educational, Scientific and Cultural Organisation as Rhodic Ferralsol. A nitrogen-free pot trial was also carried out using soil substrate sampled from the Atlantic Ocean beach. In the N-free medium, N content of the whole soybean cultivars ranged from 2.6 to 8.1 mg N per plant compared with an average of 1.8 mg N per plant observed with the non-fixing soybeans. Plant δ15N of the nodulating soybeans ranged from −2.7756‰ (Jupiter) to 0.1951‰ (Conquista), while the non-nodulating cultivars Chippewa and Clay had 2.67‰ and 9.30‰, respectively. Percentage and amount of N derived from air (Ndfa) were significantly different (P < 0.01) among soybean cultivars, and values depended highly on the selected reference plants. When Clay was used as the reference plant, the average percentage Ndfa was 1.4 times higher than when Chippewa was the reference plant. Both reference plants consistently ranked promiscuous soybean cvs. TG× 1894 3F and TG× 1908 8F as the best cultivars and cv. TG× 1888 29F as the least in percentage Ndfa, suggesting that any of the reference plants could be used in δ15N method for assessing N2-fixation. The two identified promiscuous soybean cultivars with greatest capacity to fix N could be included in a soybean extension program for West African farming systems.

Soil porous system changes quantified by analyzing soil water retention curve modifications

Soil water retention curves (SWRCs) relate soil water pressure head ( h) to soil water content ( θ) and can also be used to find information regarding soil pore distribution. To analyze SWRCs in relation to pore size distribution (PSD), changes due to wetting and drying (W–D) cycles were studied in three different tropical soils (Geric Ferralsol, GF; Eutric Nitosol, EN; Rhodic Ferralsol, RF), using three different treatments: T 0, the control with samples not submitted to W–D cycles; T 3, samples submitted to three consecutive W–D cycles; T 9, samples submitted to nine consecutive W–D cycles. Log-normal PSD equations for each treatment were obtained using the S-theory. For the GF soil, the pressure heads separating structural and matrix domains ( h s) were 17.7, 12.2 and 14.7 kPa for T 0, T 3, and T 9, respectively. These values are equivalent to pore radia of 8.4 μm ( T 0), 12 μm ( T 3), and 10 μm ( T 9). For the RF soil, h s values were 8.5 kPa ( T 0), 20.5 kPa ( T 3), and 15.1 kPa ( T 9), equivalent to radia of 18 μm ( T 0), 7.3 μm ( T 3), and 9.9 μm ( T 9); and finally, for the EN soil, h s were 18.1 kPa ( T 0), 9.1 kPa ( T 3), and 13.5 kPa ( T 9), equivalent to radia of 8.2 μm ( T 0), 16 μm ( T 3), and 11 μm ( T 9). It was found that the soil structure presented important changes in PSD due to W–D cycles for all the investigated soils. It was also observed that the W–D cycles increased the S inf (slope of SWRC) value for the GF soil for all treatments; S inf did not substantially change in all treatments for the EN soil; S inf decreased between T 0 and T 3, and T 0 and T 9 for the RF soil. According to the S-theory, it is possible to infer that W–D cycles improved the soil structure of GF, made the RF soil structure worse and did not substantially change the EN soil structure.

Fluxes of nitrous oxide from soil under different crop rotations and tillage systems in the South of Brazil

The zero tillage (ZT) system is used in a large area (>24 Mha) of crop production in Brazil. This management system can contribute to soil C sequestration, but many studies in other countries have registered greater nitrous oxide emissions under ZT compared to conventional tillage (CT), which may reduce greenhouse gas mitigation benefits. The aim of this study was to estimate the emission of N2O from cropping systems under conventional and zero tillage in an 18-year-old experiment conducted on a Rhodic Ferralsol in the South of Brazil. Fluxes of N2O were measured over two years using static-closed chambers in the two tillage systems with three crop rotations. Soil water filled pore space (%WFPS) and soil mineral N were monitored along with rainfall and air temperature. Estimates of N2O emissions were obtained by integrating the fluxes with time and also by applying the IPCC direct emission factor (EF1 = 1%) to the amounts of N added as fertilisers and returned as crop residues. Fluxes of N2O were relatively low, apart from a short period at the beginning of measurements. No relationship between N2O fluxes and %WFPS or mineral N were observed. Nitrous oxide emissions were not influenced either by tillage system or crop rotation. For the crop rotation receiving high rates of N fertiliser in the second year, field-measured N2O emissions were significantly underestimated by the IPCC emission factor 1 (EF1). For the other treatments measured N2O emissions fell within the EF1 uncertainty range, but always considerably lower than the EF1 estimate, which suggests IPCC EF1 overestimates true N2O emissions for the Ferralsol under evaluation.

The mechanism of chromate sorption by three variable charge soils

Adsorption of chromate and desorption of the pre-adsorbed chromate were studied using three representative variable charge soils from the south of China. The mechanisms of the adsorption were discussed based on the hydroxyl release and the change of ζ potential during the chromate adsorption. The adsorption and desorption of chromate followed the same order: the Hyper-Rhodic Ferralsol > the Rhodic Ferralsol > the Haplic Acrisol. The adsorption and the desorption both increased with elevation of the equilibrium chromate concentration and decreased with increasing of the soil solution pH. The percentage of the specific adsorption of chromate was 54.0–59.4%, 54.3–60.3%, and 43.9–46.2% for the Hyper-Rhodic Ferralsol, the Rhodic Ferralsol, and the Haplic Acrisol, respectively; the percentage of the electrostatic adsorption was 40.0–46.6%, 39.7–45.8%, and 50.8–56.5% for the three soils, respectively. These findings suggest that both the specific adsorption and the electrostatic adsorption contributed to the chromate adsorption by the variable charge soils. The hydroxyl release during the chromate adsorption shared the same trend with the adsorption envelopes, and decreased with increasing of pH. This is attributed to the exchange of chromate with the hydroxyl on the soil particle surfaces and the formation of a chemical bond between chromate and the surface. Our results indicate that the adsorption of chromate resulted in a shift of ζ potential-pH curves of the soil colloids to negative values, which suggests that the adsorption increased the negative surface charge and decreased the surface potential of the soil colloids.

Comparação de métodos de determinação de carbono orgânico total no solo

O teor de C orgânico total do solo (COT) pode ser determinado por métodos que se baseiam nos princípios de combustão a seco e combustão úmida. Ambos apresentam inconvenientes, principalmente o de combustão úmida, que exige grande quantidade de reagentes, gerando, por conseqüência, alta quantidade de resíduos tóxicos que contêm Cr. O método denominado Mebius no bloco de digestão (Mebius no bloco) permite a diminuição do uso de dicromato de potássio em análises de solo. Nesse sentido, o presente estudo objetivou verificar a precisão e exatidão do método Mebius no bloco em relação a outros de combustão úmida e o de combustão a seco. O trabalho foi realizado na Universidade Federal de Santa Maria, em duas etapas: os teores de COT foram determinados em 18 amostras de duas camadas (0-5 e 5-10 cm) de um Latossolo Vermelho distrófico típico com diferentes usos. Os métodos usados foram Walkley-Black, Mebius modificado, Mebius no bloco e por captura de CO2; os teores de COT foram determinados por combustão a seco e Mebius no bloco em 75 amostras coletadas nos horizontes A1 (0-7,5 e 7,5-15 cm), A2, E e Bt de um Argissolo Vermelho-Amarelo distrófico abrúptico submetido a cinco sistemas de manejo e três repetições. A precisão apresentada pelos métodos de combustão úmida é similar e com coeficiente de variação abaixo de 10 %, com exceção do método de captura de CO2, que apresentou valores de COT inferiores aos dos demais e com maior coeficiente de variação. O método Mebius no bloco permite processar maior número de amostras por tempo, com menor consumo de reagentes, e seus resultados apresentam boa precisão (coeficiente de variação menor que 2,60 %) entre os métodos de combustão úmida testados. Um fator de correção de 1,14 deverá ser aplicado aos resultados obtidos pelo método Mebius no bloco para equivaler aos obtidos por combustão a seco (analisador elementar de carbono).

Micro-morphological analysis of the effect of sampling by the volumetric ring method on soil structure

This report investigates the effect of sampling by the volumetric ring method on pore size number and shape distributions. Soil porosity was analyzed using the micromorphological image analysis technique, which helped to explain soil structure changes near the border of samples collected in cylinders and provided detailed information about pore shape, number, and size distribution variations along the samples. Compaction due to sampling affects mainly large irregular and rounded pores of the soils utilized in this study. When evaluating inaccuracies in density measurements due to the compacted regions caused by the sampling device the average soil bulk density for each soil resulted in the ranges of 1.72 ± 0.05 g.cm −3 for Geric Ferralsol soil, 1.66 ± 0.03 g.cm −3 for Eutric Nitosol soil and 1.33 ± 0.05 g.cm −3 for Rhodic Ferralsol soil, respectively. When calculating the average soil bulk density over smaller regions, e.g. in the center of each sample (area of 17.14 mm 2 ) results reduced to 1.64 ± 0.05 g.cm −3 with Geric Ferralsol soil, 1.56 ± 0.03 g.cm −3 with Eutric Nitosol soil and 1.29 ± 0.10 g.cm −3 with Rhodic Ferralsol soil, respectively. These results clearly indicate the effect of sampling by the volumetric ring method. The use of image analysis was essential to explain compaction differences close to the border of the samples collected using cylinders (volumetric ring method) and provided detailed information about pore shape and size distribution variations within soil samples. The results are useful as indicators of the consequences of sampling on the quality of soil samples.

Micromorphological analysis to characterize structure modifications of soil samples submitted to wetting and drying cycles

Abstract The physical characteristics of the soil surface are of extreme importance in relation to energy and matter transfer processes between the atmosphere and the soil. Soil internal structure changes can be due to natural or artificial causes and one important natural process is the alternation of wetting and drying (W–D) processes, which induce swelling and shrinking of soil particles, causing modifications in pore size and shape. To study the consequence of these W–D events on possible modifications in pore size distribution, pore number, and pore shape of soil samples collected in metal rings pore image analysis was used. Samples were taken from profiles of three soils of different characteristics, named as Geric Ferralsol (GF), Eutric Nitosol (EN), and Rhodic Ferralsol (RF). Confined volumetric samples (50 cm3) were submitted to none (T0), three (T1), and nine (T2) subsequent W–D cycles. Image cross sections of resin impregnated soil permitted the micrometric and macrometric characterization of changes in soil structure induced by sequences of W–D cycles. Duncan's statistical test indicated that there were significant differences (α = 0.05) among treatments for all soil samples. General conclusions indicate that total pore area increased for all soils after repeated W–D processes, specifically 19.0 to 28.9% for GF, 5.9 to 11.7% for EN, and 13.0 to 17.2% for RF. Main changes of pore diameter occurred in pores larger than 500 μm, and minor changes were observed in the total number of these pores. It is demonstrated that soil samples undergo important changes in their structures after repeated W–D cycles. The information presented here is very important for the evaluation of soil water retention curves and other soil hydric properties, because soil samples used in these procedures are collected in rings and frequently submitted to several W–D cycles.