Marcio Roberto Soares

Contribution of Soil Organic Carbon to the Ion Exchange Capacity of Tropical Soils

ABSTRACT Highly weathered soils represent about 3 billion ha of the tropical region. Oxisols represent about 60% of the Brazilian territory (more than 5 million km2), in areas of great agricultural importance. Soil organic carbon (SOC) can be responsible for more than 80% of the cation exchange capacity (CEC) of highly weathered soils, such as Oxisols and Ultisols. The objective of this study was to estimate the contribution of the SOC to the CEC of Brazilian soils from different orders. Surface samples (0.0 to 0.2 m) of 30 uncultivated soils (13 Oxisols, 6 Ultisols, 5 Alfisols, 3 Entisols, 1 Histosol, 1 Inceptisol, and 1 Molisol), under native forests and from reforestation sites from São Paulo State, Brazil, were collected in order to obtain a large variation of (electro)chemical, physical, and mineralogical soil attributes. Total content of SOC was quantified by titulometric and colorimetric methods. Effective cation exchange capacity (ECEC) was obtained by two methods: the indirect method—summation—estimated the ECECi from the sum of basic cations (Ca+ Mg+ K+ Na) and exchangeable Al; and the direct ECECd obtained by the compulsive exchange method, using unbuffered BaCl2 solution. The contribution of SOC to the soil CEC was estimated by the Bennema statistical method. The amount of SOC varied from 6.6 g kg−1 to 213.4 g kg−1, while clay contents varied from 40 g kg−1 to 716 g kg−1. Soil organic carbon contents were strongly associated to the clay contents, suggesting that clay content was the primary variable in controling the variability of SOC contents in the samples. Cation exchange capacity varied from 7.0 mmolc kg−1 to 137.8 mmolc kg−1 and had a positive correlation with SOC. The mean contribution (per gram) of the SOC (1.64 mmolc) for the soil CEC was more than 44 times higher than the contribution of the clay fraction (0.04 mmolc). A regression model that considered the SOC content as the only significant variable explained 60% of the variation in the soil total CEC. The importance of SOC was related to soil pedogenetic process, since its contribution to the soil CEC was more evident in Oxisols with predominance of Fe and Al (oxihydr)oxides in the mineral fraction or in Ultisols, that presented illuviated clay. The influence of SOC in the sign and in the magnitude of the net charge of soils reinforce the importance of agricultural management systems that preserve high levels of SOC, in order to improve their sustainability.

Copper adsorption as a function of solution parameters of variable charge soils

Effects of pH and ionic strength (I) on copper (Cu) adsorption and the driving force of the reaction in variable charge soils were evaluated from batch studies. Experimental results of Cu adsorption fitted Langmuir model. According to adsorption isotherms, Cu affinity (KL) was greater in the subsoil (0.061-0.468 L kg-1) than in the topsoil samples (0.169-0.359 L kg-1). Maximum adsorption (Adsmax) ranged from 1114-2422 mg kg-1 (topsoil) to 1002-1334 mg kg-1 (subsoil). Strong dependence of Cu adsorption on the pH was observed in subsoil samples. Adsorption edges showed sharply increase of Cu adsorption (20-90%) in the 4.0-5.0 pH range. Copper adsorption changed with increase in I and indicated different metal retention mechanisms (outer- and inner-spheres). Adsorption reaction was favorable and spontaneous, as indicated by negative values of the free energy variation (ΔG) and the separation factor KR < 1. Soil-solution interface and Cu adsorption were also thermodynamically described by a theoretical approach.

Zinc adsorption in highly weathered soils

The objective of this work was to assess the effects of pH and ionic strength upon zinc adsorption, in three highly weathered variable charge soils. Adsorption isotherms were elaborated from batch adsorption experiments, with increasing Zn concentrations (0-80 mg L -1 ), and adsorption envelopes were constructed through soil samples reactions with 0.01, 0.1 and 1 mol L -1 Ca(NO3)2 solutions containing 5 mg L -1 of Zn, with an increasing pH value from 3 to 8. Driving force of reaction was quantified by Gibbs free energy and separation factor. Isotherms were C-, H- and L-type and experimental results were fitted to nonlinear Langmuir model. Maximum adsorption ranged from 59-810 mg kg -1 , and Zn affinity was greater in subsoil (0.13-0.81 L kg -1 ) than in the topsoil samples (0.01-0.34 L kg -1 ). Zinc adsorption was favorable and spontaneous, and showed sharply increase (20-90%) in the 4-6 pH range. No effect of ionic strength was observed at pH values below 5, because specific adsorption mechanisms predominated in the 3-5 pH range. Above pH 5, and in subsoil samples, Zn was adsorbed by electrostatic mechanisms, since ionic strength effect was observed. Despite depth and ionic strength effects, Zn adsorption depends mainly on the pH.

Effect of Ionic Strength and pH on Cadmium Adsorption by Brazilian Variable‐Charge Soils

Batch adsorption experiments were conducted to assess the effects of pH and ionic strength (I) on cadmium (Cd) adsorption by two Brazilian Oxisols. Adsorption envelopes were constructed through soil sample reactions with 0.01, 0.1, and 1 mol L−1 calcium nitrate [Ca(NO3)2] solutions containing 5 mg L−1 of Cd, with an increasing pH value from 3 to 8. The adsorption increased drastically with increasing pH, varying from 20 to 90% in a narrow pH range (4–6 in topsoil and 5–6 in subsoil). Gibbs energy (ΔG) for Cd adsorption was negative, and the phenomenon became more thermodynamically spontaneous with an increase in pH. Under the standard 0.01 mol L−1 I and at pH close to natural, the ΔG values ranged from −796 to −3427 J mol−1. No effect of I was observed on the ΔG values for Cd adsorption at pH values less than 6. At values greater than pH 6, sharp changes in the Cd adsorption pattern were observed on subsoil samples. The only soil attribute significantly correlated with the spontaneity of Cd adsorption was the effective cation exchange capacity, ECEC (r = 0.97; p < 0.1).

Adsorção de boro em solos ácricos em função da variação do pH

Boron (B) adsorption by soils affects its bioavailable contents and contamination potential. The objectives of this study were: (a) to investigate the effects of pH variation on B adsorption by topsoil and subsoil samples from an Anionic Rhodic Acrudox (RA), an Anionic Xanthic Acrudox (XA) - both with a positive balance of charge in Bw horizon - and a Rhodic Kandiudalf (RK); (b) to evaluate the ability of the Langmuir model of simulating the experimental results of B adsorption; and (c) to correlate chemical, physical and mineralogical soil attributes with the values of maximum adsorption (Adsmax) and affinity coefficient (KL), derived from the isotherms. To quantify the amount of adsorbed B, batch experiments were carried out using a 0.01xa0molxa0L-1 NaCl solution as a support electrolyte containing 0.1; 0.2; 0.4; 0.8; 1.2; 1.6; 2.0 and 4.0xa0µgxa0mL-1 of B. An increase of B adsorption was observed after raising the pH (between 3.5 and 8.0) and the initial concentration of added B. Larger amounts of B were adsorbed in topsoil samples from RK and in Bw positively charged horizons from acric Oxisols. Boron adsorption was represented by type-C (linear) and type-L (exponential) isotherms and well fitted by the Langmuir model. Adsmax and KL, estimated by nonlinear regressions, were not correlated with the pH. At a natural pH, the organic matter (OM) and clay contents influenced Adsmax most in the topsoil samples. In the subsoil layers, Adsmax was negatively correlated with OM contents and positively correlated with gibbsite contents. At a natural pH, the contents of free and amorphous Fe (hydr)oxides were correlated with KL xa0values from subsoil samples. After pH increase, the oxide contents were correlated with Adsmax values from the topsoil samples.

Adsorção de selênio em latossolos

Selenium (Se) retention by soil colloids is an important process to maintain the environmental quality. Little information is available on Se adsorption in highly weathered tropical soils, and there are few numerical parameters that can be used as references to aid on adoption management strategies in contaminated areas. Increasing amounts of Se (5, 10, 25, 50, 100 and 250 mg L-1), added as Na2SeO3, were equilibrated with samples of ten Brazilian Oxisols [three Typic Hapludoxes (TH-1, TH-2 and TH-3), two Rhodic Eutrudoxes (RE-1 and RE-2), two Xanthic Hapludoxes (XH-1 and XH-2), one Rhodic Hapludox (RH), one Rhodic Acrudox (RA) and one Anionic Acrudox (AA)]. Adsorption isotherms were obtained and the experimental results fitted to Langmuir and Freundlich models. The Langmuir equation fitted better to the experimental data than the Freundlich model. All isotherms had an L-type (exponential) shape, except for TH-1 and TH-2, which had a C-type (linear) shape. Selenium Adsmax varied between 135 mg kg-1 (TH-3) and 2.245 mg kg-1 (XH-1) and the affinity constant (KL) varied from 0.002 (TH-2) to 0.326 L kg-1 (TH-3). Affinity constant (Kf) values between 13.7 (TH-2) and 180.1 L kg-1 (AA) were obtained from the Freundlich model. A high Se retention potential was observed on RH and on acric Oxisols (AA and RA), while qualitative parameters indicated RE-2, RH, TH-3 and RA as Oxisols with high Se affinity. No correlations were observed between soil attributes and Langmuir parameters. The Freundlich coefficient (Kf) correlated with clay content (r = 0.42*) and with anion exchange capacity (AEC) (r = 0.64*).

Nickel Adsorption by Variable Charge Soils: Effect of pH and Ionic Strength

The effects of pH and ionic strength (I) on Ni adsorption in variable charge soils were evaluated by laboratory batch experiments. Experimental results fitted the Langmuir model. Maximum adsorption (Adsmax) ranged from 260-2818 mg kg-1 (topsoil) to 532-1541 mg kg-1 (subsoil). Nickel affinity (KL) was higher in the subsoil samples (0.022-0.236 L kg-1) than in topsoil (0.003-0.049 L kg-1). Adsorption envelopes showed sharp increase in Ni adsorption (20-90%) in the 4.0-6.0 pH range. Nickel adsorption was affected by I and specific adsorption predominated in the 3.0-5.0 pH range, while above pH 5.0, it was adsorbed by electrostatic mechanisms. Negative values of free energy variation (ΔG) and the separation factor KR<1 indicated that Ni adsorption reaction was favorable and occurred spontaneously, especially when pH increase. Chemical and mineralogical soil attributes should be considered as criteria for selecting the areas for disposal of residues containing Ni to minimize the impact on the environment.

Effects of the addition of functional electrical stimulation to ground level gait training with body weight support after chronic stroke

BACKGROUNDnThe addition of functional electrical stimulation (FES) to treadmill gait training with partial body weight support (BWS) has been proposed as a strategy to facilitate gait training in people with hemiparesis. However, there is a lack of studies that evaluate the effectiveness of FES addition on ground level gait training with BWS, which is the most common locomotion surface.nnnOBJECTIVEnTo investigate the additional effects of commum peroneal nerve FES combined with gait training and BWS on ground level, on spatial-temporal gait parameters, segmental angles, and motor function.nnnMETHODSnTwelve people with chronic hemiparesis participated in the study. An A1-B-A2 design was applied. A1 and A2 corresponded to ground level gait training using BWS, and B corresponded to the same training with the addition of FES. The assessments were performed using the Modified Ashworth Scale (MAS), Functional Ambulation Category (FAC), Rivermead Motor Assessment (RMA), and filming. The kinematics analyzed variables were mean walking speed of locomotion; step length; stride length, speed and duration; initial and final double support duration; single-limb support duration; swing period; range of motion (ROM), maximum and minimum angles of foot, leg, thigh, and trunk segments.nnnRESULTSnThere were not changes between phases for the functional assessment of RMA, for the spatial-temporal gait variables and segmental angles, no changes were observed after the addition of FES.nnnCONCLUSIONnThe use of FES on ground level gait training with BWS did not provide additional benefits for all assessed parameters.

Characterization of the soil fertility and root system of restinga forests

The Restinga vegetation consists of a mosaic of plant communities, which are defined by the characteristics of the substrates, resulting from the type and age of the depositional processes. This mosaic complex of vegetation types comprises restinga forest in advanced (high restinga) and medium regeneration stages (low restinga), each with particular differentiating vegetation characteristics. The climate along the coast is tropical (Koppen). Of all ecosystems of the Atlantic Forest, Restinga is the most fragile and susceptible to anthropic disturbances. Plants respond to soil characteristics with physiological and morphological modifications, resulting in changes in the architecture (spatial configuration) of the root system. The purpose of this study was to characterize the soil fertility of high and low restinga forests, by chemical and physical parameters, and its relation to the root system distribution in the soil profile. Four locations were studied: (1) Ilha Anchieta State Park, Ubatuba; (2) two Ecological Stations of Jureia-Itatins and of Chauas, in the municipality of Iguape; (3) Vila de Pedrinhas in the municipality of Ilha Comprida; and (4) Ilha do Cardoso State Park, Cananeia. The soil fertility (chemical and physical properties) was analyzed in the layers 0-5, 0-10, 0-20, 20-40 and 40-60 cm. In addition, the distribution of the root system in the soil profile was evaluated, using digital images and the Spring program. It was concluded that the root system of all vegetation types studied is restricted to the surface layers, 0-10 and 10-20 cm, but occupies mainly the 0-10 cm layer (70 %); that soil fertility is low in all environments studied, with base saturation values below 16 %, since most exchange sites are occupied by aluminum; and that restinga vegetation is edaphic.

Incorporação de régua para medida de profundidade no projeto do penetrômetro de impacto Stolf

The Stolf impact penetrometer is a dynamic cone penetrometer to measure soil resistance, in use since its release in 1982. In the original design, a centimeter scale to measure penetration depth was engraved on the proper penetration rod. The idea was to make the equipment easier to understand for farmers and to allow direct readings on the penetration rod while also avoiding additional parts. The purpose of this study was to incorporate a millimeter ruler to enable the operator to read the depth at eye level, to avoid squatting and to increase the reading accuracy. The equipment use and reset procedure of the depth reading (zero) were described and illustrated. The two reading types were compared in terms of sampling time, using a randomized block design. A significant difference (t test, 1 %) was observed, resulting in 21 % less time spent for readings on the ruler. Besides increasing the reading accuracy and reducing the sampling time, the users preferred the new design, which was finally incorporated into the commercial model. A retrospective of the technical development of the penetrometer is presented; this study represents the first modification of the project, which had remained unaltered for 30 years.