L. M. da Costa

Mobility of heavy metals as related to soil chemical and mineralogical characteristics of Brazilian soils

In order to better understand the relationship between soil characteristics and mobility of some heavy metals, correlation studies were conducted in samples of unlimed and limed A, B and C horizons of three Brazilian soils, representative of the majority of the tropical soils. A number of chemical and mineralogical characteristics of one Oxisol and two Ultisols were related to the retardation factors (Rf) for zinc (Zn), cadmium (Cd), copper (Cu) and lead (Pb). The retardation factors, obtained in leaching column experiments, were used as an estimate of solute movement in the profile. Soil types and soil horizons were found to influence metal retardation factors which, in turn, correlated better with the chemical than the mineralogical soil characteristics. For the unlimed soil samples, the soil characteristics that significantly correlated with Zn-Rf and Cd-Rf were the sum of exchangeable bases (SB), and soil exchangeable (Ca-KCl) and non-exchangeable (Ca-HCl) calcium contents. These results showed the strong influence of the cation exchange phenomenon on the retention and mobility of these two metals. For Cu and Pb, not only SB, cation exchange capacity (CEC) and Ca-KCl and Ca-HCl but also the organic matter correlated well with the Rf, showing that complex or chelate formation may play an important role in the movement of these elements. The important soil chemical characteristics related to the retardation factors in the limed soil samples were SB for Cd, and Ca-HCl for Cu and Pb, suggesting that precipitation may also influence the mobility and retention of the latter two heavy metals in these soil samples. Soil pH influenced the heavy metals adsorption and movement as shown by the significant correlation with the retardation factors when the combined data for the unlimed and limed soil samples was considered.

Pedogenesis on the uplands of the Diamantina Plateau, Minas Gerais, Brazil: a chemical and micropedological study

Abstract Little is known about the soil distribution on quartzitic uplands of Brazil. The Diamantina Plateau, where deeply weathered oxisols (latosols) and shallow sandy soils occur side by side, represents part of the higher and oldest planation on the quartzitic uplands of Minas Gerais State. We studied representative soils from the Diamantina Plateau to help understand the pedogenesis and landscape evolution of this part of Minas Gerais. We found evidence of a lithological and tectonic control on the distribution of soils in the landscape. Polygenetic oxisols (Acrustox) occur at the top of the landscape at altitudes of 1300 m or more, resting uncomformably on quartzitic saprocks (Xanthic types) or mafic rocks (Rhodic types). They change downslope to in situ Quartzpsamments and Haplorthods. In the B horizon of the Xanthic Acrustox, quartz grains smaller than 0.3 mm are surrounded by gibbsitic plasma, forming subspherical microaggregates. Microaggregates in the Bw horizon of all upland oxisols display inherited features of intense biological activity regardless of the parent material or texture. The nutrient-poor catena of Xanthic Acrustox–Ustic Quartzpsamments–Oxyaquic Haplorthods represents a sequence of increasing hydromorphic conditions downwards, in which clay minerals are destroyed in low pH and ferrolysis. In the poorly drained soils downslope, low pH and eH induce the movement of reduced Fe 2+ and organic matter (OM)-bound Al and Fe both per descendum and through lateral flow downslope. In the bottom, micromorphological features and the chemistry of organic matter indicated that some Bsh horizons represent buried A horizons subjected to post-burial podzolization, corroborating morphological field data. This indicates the pertinence of the study of humic fractions in defining the Bhs (spodic) horizons of Brazilian spodosols.

Magnetic separation and evaluation of magnetization of Brazilian soils from different parent materials

Abstract Ten selected Brazilian soils representative of Oxisols, Ultisols, Alfisols and Inceptisols and derived from gneiss, basalt, sandstone, diabase and itabirite were sampled and examined to provide insight into the behavior of their magnetic minerals. The objective was to measure the magnetization of the sand, silt and clay fractions and to submit the clay fraction to variable magnetic fields to obtain the magnetization curves and to study their magnetic behavior as related to their parent material lithology. The separation procedure using a magnetic separator was done in two different ways: dry separation for the sand and wet separation for the silt and clay fractions. X-ray diffraction patterns of magnetic and nonmagnetic fractions were obtained and the segregation of ferrimagnetic minerals were shown. The magnetization (σs) of the total and the magnetic and nonmagnetic soil fractions was evaluated using a special analytical balance. The σs values obtained varied from 0.03 to 17.72 J T−1 kg−1 for sand; 0.05 to 8.91 J T−1 kg−1 for silt and 0.05 to 2.54 J T−1 kg−1 for the clay fractions. The results from the magnetically concentrated fractions varied in the same fashion but reached higher values. Magnetization curves showed spontaneous magnetization (Ms) values of 0.6 to 3.35 J T−1 kg−1, high field slopes (λ) ranging from 0.17 to 0.77 J T−2 kg−1 and, clearly, the influence of the parent material lithology on the nature of the soil magnetic behavior. Magnetic measurements suggested pathways for ferrimagnetic minerals transformations in soil systems.

Extração fracionada de metais pesados em latossolo vermelho-amarelo

Samples of A and B horizons of a humic red-yellow latosol with a clayey texture were incubated in salt solutions of Cd, Cr, Cu, Ni, Pb and Zn under greenhouse conditions at the Universidade Federal de Vicosa, Brazil, from March to September 1994. The main objectives were to adapt a method for fractional extraction of metals and to evaluate their behavior in soluble, exchangeable, bound to organic matter, bound to Al oxides, bound to Fe oxides, and residual forms. The experiment consisted of two horizons and two concentrations of metal, arranged in a randomized block design with three replications. After 17 hours of incubation, the samples were air dried, homogenized, passed through a 2 mm sieve and stored in plastic bags for subsequent extraction of the metals. The samples were subjected to the methodology of fractional extraction and the evaluation of the treatment with NaOH to characterize the oxides of Al was made. The fractional extraction showed to be adequate for studying the behavior of heavy metals in soil. The Cd was found mainly in the soluble and exchangeable forms and Cr in the more stable chemical forms (bound to Fe oxides and residual); Cu and Pb presented highest affinities towards Fe oxides and organic matter, respectively. Ni was found mainly in the residual form and showed lower affinity for organic matter. The study of Zn behavior was not possible, due to the contamination of extracts stored in flasks with rubber caps. There is still a need to improve a methodology to characterize metals associated with Fe and Al oxides.

Comportamento do algodoeiro herbáceo (Gossypium hirsutum latifolium Hutch.) e controle de plantas daninhas com o uso dos herbicidas diuron e sethoxydim

To verify the behavior of the c. IAC -17, as well as, the control of weeds and competitive aspects of the infesting floristic complexes over the cotton culture under the presence of the herbicides, diuron and sethoxydium, atrial was contucted in Vicosa, Minas Gerais. The soil at the experimental site, Podzolic Red-yellow, had a clay texture wi th 1,38% of organic carbon an low natural fertility. Diuron was applied at pre -emergence time at the rates of 0, 0; 0, 8; 1,6 and 2,4 kg a.i. /ha and sethoxyd im at post-emergence at the rates of 0, 150, 300, 450 and 600 g a.i./ha. The trial was setup in a randomized blocks design with 2 1 treament sunder a factorial scheme (x 5 + 1) . Out of them, 20 composed all the combinations with different dosis of the two herbicides under study plus a relative control weeded with the aind of a mattock. Several traits concerning growth and plant development were evaluated, such as leaf area, leaf area in dex, seed -cotton yield, plant height, stem diameter. By means of syn ecological methods, th e population density, hydrated epigeous phytomase of dominant weed species, and the total of all species were evaluated. Diuron exerted a high control overlati foliates such as Galinsoga parviflora Cav . and Bidens pilosa L., at the rates of 1, 6 an d 2,4 kg a. i. /ha, seth oxydim, even using the lowvest tested rate (150 g. a. i. /h a) fully controled Brachiaria plantaginea (Link.) Hitch. None of th e herbicides was able to control Emilia sonchifolia DC. Th is species although being considered an important weed did not affect the normal crop development because of its low competition ability. The weeds showing highes trates of competition were G. parviflora (due to high population density) an d B. plantaginea, because of its greater aggresivity.

Resistência de espécies e cultivares de algodão (Gossypium spp.) ao herbicida diuron

To determine the resistance of cotton species and cultivars to the herbicide diuron, a green house test was conducted in Vicosa, Minas Gerais. Genotypes of the species Gossypium: hirsutum latifolium Hutch. ( cv IAC 17 and BR 1) , G. hirsutum marie galante Hutch. (cv Veludo C 17) , and G. barbadense brasiliense Hutch. (cv rim-de-boi ) were studied . A split plot in a randomized complete block design was utilized in this experiment. The main plots were the herbicid e dosage (0,0 0, 0,0 48, 0,0 96, 0, 35 7, 0, 71 4 an d 1, 42 8 kg a. i. /h a) applied to the sand subs trat when the plants had one or two true leaves, and the subplot were the genotypes. Each plot was represented by a wood bos (3 7 x 47 x 11/cm) filled with washed sand. The seeds were acid deslinted before planting. To measure the resistance several parameters were observed such as: Phitotoxicity level 15 days after application, plant height, fresh and dry weight of plants, rate of stem elongation and rate of relative growth of aerial part. The results showed that cv IAC 17 and BR -1 were the most resistant to the chemical stress of the herbicide, the cv Veludo C 71 had in termediate resistance being the cv Rim de Boi the kg a . i . /ha was ha rmful to the plants of this cultivar. The results indicates that one should consider the specie and cultivar, before recommend ingthe application of diuron to a cotton field.

Efeitos do controle de plantas daninhas, com herbicidas, na produção e qualidade fisiológica de sementes de feijoeiro (Phaseolus vulgaris L.)

This experiment was planned to evaluate the effect of herbicides on yield and physiological quality of field bean seeds. A trial was carried out on a Cambic yellow Podzolic, terrace fase clay soil, with 2,8% of organic matter. The following treatments were applied: a) mechanically weeded; b) non-weeded; c) EPTC at 5.70 kg a.i./ha; d) trifluralin at 0.75 a.i./ha; e) EPTC 2,00 kg a.i./ha + trifluralin at 0.60 kg a.i./ha; f) nitralin at 1.00 kg a.i./ha e pendimethalin at 1.50 kg a.i./ha. Seed physiological quality was determined by the fo llowing te sts: acce lerated aging, first count germination, standard germination and weight of seed dry matter. The prevalent weeds in the field were Oxalis sp, Galinsoga parviflora and Cyperus rotundus. The standard germination test was not a good method to assess seed vigor. Trifluralin was not detrimental to the accumulation of dry matter in seedlings. The accelerated aging test was effective to differentiate treatments, showing that seeds from non-weeded plots had less vigor than seeds from plots treated with EPTC + trifluralin.