Renildes Lúcio Ferreira Fontes

Fracionamento, dessorção e extração química de zinco em latossolos

Knowledge of the chemical forms of Zn in the soil and the relationships with soil available concentrations are important for predicting its behavior. This work aimed to study the influence of zinc on the desorption, extraction and fractioning of Zn in samples from six Oxisols. The soil samples, with and without lime application, were kept incubated for 30 days after receiving Zn doses (0.0, 20, and 40 mg dm-3). After incubation, the micronutrient was extracted with Mehlich-1, Mehlich-3, DTPA and EDTA. Additionally, the samples were fractionated for Zn determination in the fractions: exchangeable, organic matter, manganese oxides, amorphous iron oxides, crystalline iron oxides, and residual fraction, as well as the total concentrations of the micronutrient. The micronutrient desorption was evaluated by successive extractions with cation exchange resin. It was concluded that, without liming, the application of the Zn doses to the soil resulted in retention of Zn mainly in the exchangeable and organic matter fractions. In general, liming reduced the exchangeable contents and increased organic matter, amorphous and crystalline iron, and manganese oxide fractions. Without liming, Zn in the exchangeable fraction was highly correlated with all extractors. With liming, all extractors presented high correlation with Zn in the organic matter fraction. Without liming, Zn lability in the fractions decreased in the order: Ex = OM > MnOx > AFeOx >> CFeOx, for EDTA. Mehlich-1, and Mehlich-3, presented best correlations with the total desorbed zinc amounts, while liming caused absence of Zn desorption.

Mineral composition of two Brazilian corn cultivars as a function of cadmium in the nutrient solution

Abstract Plants from the Brazilian corn (Zea mays L.) cultivars CMS 54 and BR 473 were grown in nutrient solutions with 0.0, 0.05, 0.1, 0.5, and 1.0 mg cadmium (Cd) L‐1 for a ten day period. The experiment was a completely randomized block design with the treatments arranged in a 2×5×3 factorial, two corn cultivars, five Cd rates, and three replications. The influence of the Cd rates on the nutritional status of the corn plants was studied. Samples from roots and shoots were analyzed for their Cd, phosphorus (P), potassium (K), sulfur (S), calcium (Ca), magnesium (Mg), iron (Fe), zinc (Zn), and copper (Cu) contents. At rates above 0.5 mg Cd L‐1, there was an influence of exogenous Cd on the elemental composition of the plants. It seems that with rates above 0.5 mg Cd L‐1, the influence of Cd on the P status of the shoots took place in the CMS 54 but not in the BR 473 cultivar. Similar results for K, Ca, Mg, and S were found. There was competition between the Cd and Zn ions at the absorption sites in the p...

Iron deficiency and zinc toxicity in soybean grown in nutrient solution with different levels of sulfur

Abstract A typical symptom of iron (Fe) deficiency in plants is yellowing or chlorosis of leaves. Heavy metal toxicity, including that of zinc (Zn), is often also expressed by chlorosis and may be called Fe chlorosis. Iron deficiency and Zn toxicity were evaluated in soybean (Glycine max [L.] Merr.) at two levels each of Zn (0.8 and 40 μM), Fe (0 and 20 μM), and sulfur (S) (0.02 and 20 mM). Reduction in dry matter yield and leaf chlorosis were observed in plants grown under the high level of Zn (toxic level), as well as in the absence of Fe. Zinc toxicity, lack of Fe, and the combination of these conditions reduced dry matter yield to the same extent when compared to the yield of the control plants. The symptoms of Zn toxicity were chlorosis in the trifoliate leaves and a lack of change in the orientation of unifoliate leaves when exposed to light. The main symptoms of Fe deficiency were chlorosis in the whole shoot and brown spots and flaccid areas in the leaves. The latter symptom did not appear in plan...

ACCUMULATION AND DISTRIBUTION OF ABOVEGROUND BIOMASS AND NUTRIENTS IN PURE AND MIXED STANDS OF GUACHAPELE AND EUCALYPTUS

ABSTRACT The biomass accumulation and the distribution of nutrients in the different components of the aerial parts (leaves, branch, bark, and wood) of pure and mixed stands of guachapele [Pseudosamanea guachapele (Kunth) Harms] and eucalyptus (Eucalyptus grandis W. Hill ex Maiden) were quantified in Seropédica, Rio de Janeiro State, Brazil. Mixed stands had the highest production of stem tissue (204 m3/ha), in contrast with the pure plantations of each species (78.1 m3/ha for guachapele and 199 m3/ha for the eucalyptus). Total dry biomass of eucalyptus was 1.6 times more than that of guachapele in monoculture and 6.8 times larger than that in the mixed stands. The eucalyptus had 10% less biomass in mixed stands than in pure stands. Despite production of less biomass, the guachapele had more nutrient uptake, accumulating, as a pure stand, 484.68 kg/ha of nitrogen (N), 35.0 kg/ha of phosphorus (P), 274.5 kg/ha of potassium (K), 223.8 kg/ha of calcium (Ca), and 40.7 kg/ha of magnesium (Mg). The eucalyptus plants were more efficient in the utilization of N, P, K, Ca, and Mg than the guachapele and this efficiency was increased in the mixed stands. Among the treatments the litter layer, in the pure stand of guachapele contained the highest quantities of N (273.1 kg/ha) and P (8.2 kg/ha), while the pure stands of eucalyptus of K (22.6 kg/ha), Ca (163.8 kg/ha), and Mg (28 kg/ha).

Critical phosphorus concentrations in potato plant parts at two growth stages

Abstract Adequately evaluating the phosphorus (P) nutritional status of a potato crop is dependent upon sampling the appropriate plant part at a defined growth stage. To establish P critical concentration levels in various potato plant parts (leaves, stems, tubers, leaflets, and petioles) at two growth stages [20 and 50 days after plant emergence (DAE)], an experiment under Brazilian climatic and soil conditions was conducted using seven P treatment levels (0, 40, 80, 160, 320, 640, and 1,280 kg P2O5 ha‐1) applied in a randomized complete block design with four replications. ‘Baraka’ potato tubers were seeded at a spacing of 0.80 x 0.30 m following agronomic cultural practices recommended for this crop. Phosphorus concentrations in all the potato plant parts were significantly affected by the P fertilizer rates applied. The highest correlation between the P concentration in the various plant parts and marketable yield and optimum profit yield was obtained for the petiole taken 20 days DAE. Critical P leve...

Copper availability as related to soil copper fractions in oxisols under liming

The knowledge of the chemical forms of copper in soils and the relationships of these forms with soil copper availability are important for predicting the copper behavior in the soil-plant system. The present work studies the influence of liming on the available contents of copper as well as on the forms of copper fractions in six types of Oxisols. Soil samples, with and without liming, received copper at rates of 0.0, 20.0 and 40.0 mg dm-3 and remained incubated for 30 days. Then, available copper was extracted with Mehlich-1, Mehlich-3, DTPA and EDTA solutions, and analyzed by atomic absorption spectrophotometry. Additionally, soil samples were extracted in a sequential procedure to determine Cu in fractions of soil, as follows: exchangeable-Cu fraction, organic matter-Cu fraction, Mn oxide-Cu fraction, amorphous Fe oxide-Cu fraction, crystalline Fe oxide-Cu fraction, residual-Cu fraction, and the total Cu content in the soil. Soil samples to which Cu was added presented higher Cu retention in the organic matter fraction with a small percentage retained in the exchangeable-Cu fraction. Liming resulted in a decrease of Cu in the exchangeable and organic matter fractions and an increase in the Fe and Mn oxide fractions and in the residual fraction. Without liming, the organic matter fraction presented the highest contribution to Cu content found in the soil extracts obtained with all extractors, except EDTA. For treatments with liming, Cu contents in the organic matter fraction were better correlated to Cu contents in extracts obtained with DTPA and Mehlich-3.

Effects of zinc fungicides and different zinc fertilizer application methods on soluble and total zinc in potato plant shoots

Abstract The experiment was carried out to evaluate the effects of fungicides [with or without zinc (Zn)] and different Zn fertilizer application methods (no fertilizer; soil application; shoot application; soil plus shoot application) on the soluble and total Zn in the dry matter of potato shoots. Zinc fertilizer was applied to the shoots at 20 and 45 days after plant emergence (DAE), immediately before plant sampling. At 25 DAE, Zn fungicide increased soluble and total Zn in the fourth leaf. The same occurred, at 45 DAE, with the Zn fertilizer applied to the shoots. It were not observed significant increases on both soluble and total Zn contents in the fourth leaf of plants that received soil Zn fertilization. Even in the leaves with 262 mg Zn kg‐1, there was no phytotoxicity symptoms. The total Zn concentration at 20 DAE was the best index correlated to potato tuber yield reaching 50.9 mg Zn kg‐1 in the fourth leaf of plants at the highest marketable tuber yield treatment. Plant nutrient element conten...

Aplicação do silício para aumentar a resistência do arroz à mancha-parda

The aim of this study was to evaluate sources and methods of silicon application to improve silicon uptake and the resistance of rice plants (Oryza sativa), cultivar Metica-1, to brown spot (Bipolaris oryzae). Two experiments were carried out in a greenhouse, with an Oxisol soil, in a completely randomized design with eight repetitions. The treatments were wollastonite (calcium silicate) applied via soil and potassium silicate and silicic acid applied to the leaves. The soil-applied silicon increased the foliar silicon content and reduced the severity of brown spot, in contrast to the results observed in the foliar-applied silicon treatments.

Desenvolvimento de mudas de cedro-rosa em solo contaminado com cobre: tolerância e potencial para fins de fitoestabilização do solo

Agricultural, industrial and mining activities are the mainly factors related to soil contamination, as well the reuse of urban and/or animal residues. These activities can produce heavy metals accumulation in soils, which are potentially dangerous chemical elements to environmental quality and to well-being of living beings. Phytoremediation is a technology for rehabilitation of degraded areas which aims the soil decontamination. Forest species can immobilize and export to outside of the system larger amounts of chemical elements from contaminated soil, because they have high biomass production. The objective of this study was to evaluate the Cedrela fissilis development in contaminated soil by heavy metals. With this propose, seedlings were cultivated in greenhouse and in a contaminated soil by Cu (0, 60, 80, 100, 500 mg kg-1) for 105 days. After this period some soil and plant parameters were evaluated. Seedlings of C. fissilis presented crescent increments of dry matter until 100 mg kg-1 of Cu, with reduction of vegetal development in the high doses. In general, it was verified high partition of dry matter to root system than aerial part. Plant Cu contents were correlated with applied doses in the soil. The root bioconcentraction factor of C. fissilis indicates potential capacity of this tree specie to phytostabilization works in contaminated soils.

Determination of molybdenum in soil test extracts with potassium iodide plus hydrogen peroxide reaction

Abstract The potassium iodide and hydrogen peroxide reaction (KI+H2O2) is catalyzed by molybdate. Our objective was to use this reaction to determine molybdenum (Mo) in Mehlich 1 (1:10) soil test extracts. A 350‐nm wavelength and 10‐minute reaction time were selected for the determination and absorbance was linear for 0.0 to 0.15 mg L‐1 Mo. Ten samples of a LEd‐Iturama soil were extracted with Mehlich 1 and Mo determined. These extracts were also mixed and Mo determined on 10 aliquots of the mixture. Molybdenum concentration in the soil had a coefficient of variation (CV) of 23.5%, whereas that for the mixture was 3.95%. The low CV for the mixture indicates good precision for this method. The higher CV for the individual extracts indicates that most of the variation comes from the extraction phase of individual samples. To show the practical utility of the method, Mo maximum adsorption capacities (MoMAC) of 16 soils, primarily Oxisols, from Minas Gerais, Brazil were determined. The MoMAC varied from 0.15 to 2.02 mg g‐1 and there were good correlations between MoMAC and soil clay content as well as between MoMAC and soil organic carbon content. From our experience, use of the KI+H2O2 reaction is a practical method of determining Mo in Mehlich 1 soil test extracts.