Clesio Gianello

Potencial de mineralização do nitrogênio em solos do Rio Grande do Sul

Nitrogen mineralization potential (No) for ten Rio Grande do Sul, Brazil, soils was studied with corn grown on 20 kg pots for 45 days, as compared with nitrogen mineralized in aerobic incubation for 32 weeks. No values ranged from 108.6 to 210.8 mg kg-1, being similar to the total nitrogen mineralized. Mineralization velocity was higher during the first four weeks, and overall mineralization rate varied from 0.2985 to 0.3181 week-1 among soils. The correlation coefficient between corn absorbed nitrogen and mineralization potential was significant (0.886), indicating that this can be used as an index for soil nitrogen availability to plants.

Empirical models to predict soil nitrogen mineralization

Modelos empiricos sao equacoes matematicas que podem ser ajustadas a resultados experimentais. Esses modelos podem ser utilizados para avaliar ou predizer fenomenos observados ou dados experimentais e auxiliar no desenvolvimento de praticas adequadas de manejo do solo. Desse modo, o presente trabalho teve por objetivo comparar oito modelos matematicos descritos na literatura, utilizando como dados experimentais o N mineralizado de dez solos do Rio Grande do Sul, acumulado durante 32 semanas de incubacao. O N mineralizado foi obtido experimentalmente em um experimento de incubacao, seguido de lixiviacao com CaCl2 0,01mol L-1. O N mineral foi determinado no comeco do periodo de incubacao e ao final da 2a, 4a, 8a, 16a e 32a semanas. Entre os modelos testados, o melhor ajuste do N mineralizado foi obtido com os modelos exponenciais simples, ao passo que a obtencao desses ajustes nos modelos exponenciais duplos esteve condicionado ao aumento de parâmetros na equacao. Em funcao dos resultados observados e das condicoes experimentais, conclui-se que a hipotese em que os modelos exponenciais duplos estao baseados, isto e, na presenca de dois compartimentos de nitrogenio suscetiveis a mineralizacao, foi rejeitada.

Frações de fósforo em estrumes e sua eficiência como adubo fosfatado

Manures used as phosphorus sources may have different efficiencies from those of commercial soluble fertilizers. These efficiencies may vary according to the manure origin and to the proportions of its total P in different chemical fractions. A greenhouse experiment was conducted in order to estimate the efficiencies of dairy cattle and chicken manures as phosphorus source, in comparison to triple superphosphate (TSP), as well as to relate these efficiencies to their P fractions. The treatments were: control, without fertilizer or manure; three rates of P, applied as TSP (6.6, 13.2 and 19.7 mg kg-1 soil); and a single phosphorus application rate of 15.3 mg kg-1 soil, from 11 samples of both cattle and chicken manures. Treatment responses were evaluated cultivating millet during 27 days after P application, in pots filled with a Kandiudult soil. Manure P fractions were determined by sequential extractions. The Efficiency Index (EI), estimated by the TSP equivalence, was 0.84 ± 0.071 for chicken manure, significantly lower than that for cattle manure, 0.94 ± 0.095. There were no statistical differences in EI among manures samples of the same animal species. Considering all samples, EI was positively correlated with proportions of labile P (extracted with resin and NaHCO3) and total inorganic P and negatively correlated with proportions extracted with NaOH and HCl and with total organic P. There was no association between EI and the total P content in the manures.

Interpretação de resultados analíticos de fósforo pelos extratores Mehlich-1 e Mehlich-3 em solos do Rio Grande do Sul

Multielement soil extractant solutions are used by several soil testing laboratories to determine the plant availability of several nutrients by the same extractant, to decrease costs and labor. The Mehlich-1 (M1) and Mehlich-3 (M3) solutions are often used for this purpose. In this study, they were used to evaluate soil P availability using 360 soil samples of the State of Rio Grande do Sul (Southern Brazil). The correlation coefficients between the P concentrations extracted by these solutions were strongly associated and highly significant. The P concentrations extracted by the M3 solution were on average 50 % higher than those extracted by M1. The soil clay content affected the P extraction capacity of the M3 solution, requiring an adjustment table for the interpretation of the P value by this method, as proposed here.

Soil Nitrogen Availability Evaluated by Kinetic Mineralization Parameters

Abstract Mathematical models can be used to test or predict observed phenomena or experimental data in order to assist the development of suitable tillage practices. This article describes the kinetic nitrogen (N) mineralization parameters for the corn crop in soils from Rio Grande do Sul State, Brazil. Experiments were carried out to determine the total N mineralized over 32 weeks of incubation and the uptake by corn (Zea mays L.) plants 45 days after planting. A comparison of the experimental results with the kinetic parameters calculated using eight different algorithms showed that mineralized or potentially mineralizable N (No) was best described by the active N fraction of N mineralization. The active fraction and No, described by a hyperbolic equation, were the best predictive parameters for nitrogen availability to corn. Potentially mineralizable N could not be estimated adequately in this experiment by the double exponential models and by its parameters described as labile and recalcitrant or easily and not easily mineralizable N. The conclusion is that no different fractions estimated by mathematical equations make up the organic N content during the incubation period employed here, and that this property is best estimated by the No concept.

Comparative study of five hydrolytic methods in the determination of soil organic nitrogen compounds

Abstract An evaluation of the effectiveness of five methods for the determination of major organic‐nitrogen (N) fractions was made. The methods tested included the reflux method of Bremner (Method 1), the method of Yonebayashi and Hattori (Method 2), a successive reflux method of Gonzalez‐Prieto (Method 3), a modified method of Gonzalez‐Prieto (Method 4), and an adjustment method employing linear regression equations (Method 5). Total hydrolyzable‐N, ammonium‐nitrogen (NH4‐N), amide‐N, hexosalnine‐N, α‐amino‐N, and unidentified N were determined in the hydrolysates. The results indicated that Method 2 was the best method with a recovery value for hydrolyzed N of 60.5% of total soil N. Continuous refluxing for 12 h (Method 1) was ineffective for the determination of hexosamine N, whereas Methods 3 and 4 were satisfactory, but yielded lower recovery amounts than Method 2. Method 5 failed to estimate the proper value and new equations were formulated.

Tannery and coal mining waste disposal on soil

Tannery residues and coal mine waste are heavily polluting sources in Brazil, mainly in the Southern States of Rio Grande do Sul and Santa Catarina. In order to study the effects of residues of chrome leather tanning (sludge and leather shavings) and coal waste on soybean and maize crops, a field experiment is in progress since 1996, at the Federal University of Rio Grande do Sul Experimental Station, county of Eldorado do Sul, Brazil. The residues were applied twice (growing seasons 1996/97 and 1999/00). The amounts of tannery residues were applied according to their neutralizing value, at rates of up to 86.8 t ha-1, supplying from 671 to 1.342 kg ha-1 Cr(III); coal waste was applied at a total rate of 164 t ha-1. Crop yield and dry matter production were evaluated, as well as the nutrients (N, P, K, Ca, Mg, Cu and Zn) and Cr contents. Crop yields with tannery sludge application were similar to those obtained with N and lime supplied with mineral amendments. Plant Cr absorption did not increase significantly with the residue application. Tannery sludge can be used also to neutralize the high acidity developed in the soil by coal mine waste.

Mercury (II) removal by resistant bacterial isolates and mercuric (II) reductase activity in a new strain of Pseudomonas sp. B50A

This study aimed to isolate mercury resistant bacteria, determine the minimum inhibitory concentration for Hg, estimate mercury removal by selected isolates, explore the mer genes, and detect and characterize the activity of the enzyme mercuric (II) reductase produced by a new strain of Pseudomonas sp. B50A. The Hg removal capacity of the isolates was determined by incubating the isolates in Luria Bertani broth and the remaining mercury quantified by atomic absorption spectrophotometry. A PCR reaction was carried out to detect the merA gene and the mercury (II) reductase activity was determined in a spectrophotometer at 340 nm. Eight Gram-negative bacterial isolates were resistant to high mercury concentrations and capable of removing mercury, and of these, five were positive for the gene merA. The isolate Pseudomonas sp. B50A removed 86% of the mercury present in the culture medium and was chosen for further analysis of its enzyme activity. Mercuric (II) reductase activity was detected in the crude extract of this strain. This enzyme showed optimal activity at pH 8 and at temperatures between 37 °C and 45 °C. The ions NH4(+), Ba(2+), Sn(2+), Ni(2+) and Cd(2+) neither inhibited nor stimulated the enzyme activity but it decreased in the presence of the ions Ca(2+), Cu(+) and K(+). The isolate and the enzyme detected were effective in reducing Hg(II) to Hg(0), showing the potential to develop bioremediation technologies and processes to clean-up the environment and waste contaminated with mercury.

Avaliação da disponibilidade de fósforo no solo para a cultura do milho

In order to evaluate soil phosphorus availability to plants, the extraction methods: Mehlich-1, exchange resins in beads (RE), encapsulated (RC) and as membrane (RM) and iron oxide impregnated filter papers with 75% field capacity (D1) and waterlogged conditions (D2) were studied in Rio Grande do Sul State, Brazil, in 1994, in a greenhouse experiment with six soils fertilized with four phosphate rates and cultivated with corn (Zea mays L.) for 28 days. Determination coefficients between plant absorbed phosphorus and the amounts determined by the extraction methods were: 0.85 (Mehlich-1), 0.82 (RE), 0.84 (RC), 0.89 (RM), 0.75 (D1) and 0.70 (D2). Soil phosphorus contents extracted by the exchange resin methods were highly correlated (r=0.98), as well as with the amounts extracted by the D-1 method (r = 0.89). The results indicated that the studied methods are equally effective for predicting P availability to the corn plants.

Isolamento e seleção de micro-organismos resistentes e capazes de volatilizar mercúrio

Mercury (Hg) occurs in the environment as a natural and anthropogenic element, and through the years the accumulation of mercury has affected the integrity of ecosystems and human health. This study presents a screening of microorganisms resistant to organic and inorganic mercury, the determination of the minimum inhibitory concentration of Hg, the estimation of the mercury volatilization by selected microorganisms and the dynamics of volatilization. Eight Gram-negative bacteria resistant to high concentrations of mercury (60 to 210 mg L-1) were selected, and these isolates showed ability to volatilize the metal. The dynamics of the volatilization of the Proteus mirabilis M50C demonstrated that in only 4 h of incubation it was possible to volatilize 72% of the mercury present in the culture. The results showed promising application for bioremediation strategies.