Caio Vidor

Utilização de microondas na avaliação da biomassa microbiana do solo

The objective of this work was to determine carbon and nitrogen content in the soil microbial biomass by comparing microwave radiation and chloroform fumigation using the extraction and incubation methods. Two soil samples (Dark-Red Podzolic) were submitted to incubation and extraction after chloroform fumigation and microwave radiation during different periods (2, 5, 10, 15, 20, 30, 40 and 50 min). Two minutes under microwave radiation were sufficient to determine C and N content in the soil biomass using incubation and extraction procedures. These values were similar to those obtained by chloroform fumigation. The coefficients of variation in the soil samples submitted to microwave radiation extraction were reduced. Thus, this was considered the most adequate procedure for carbon and nitrogen quantification in soil biomass.

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.

Rendimentos de culturas e alterações químicas do solo tratado com resíduos de curtume e crômio hexavalente

This study was carried out in order to evaluate yields of wheat, lettuce and radish, as well as chemical changes in an Oxisoil due to the addition of tannery waste and hexavalent chromium. Microplots in a greenhouse, which consisted of 60 L plastic pots, received the following treatments: control; lime + NPK; primary tannery sludge + PK; chrome-tanned leather shavings + lime + NPK; finished leather shreds + lime + NPK; Cr6+ + lime + NPK; Cr6+ + lime + cattle manure; lime + cattle manure. The sludge contained 8.5 g kg-1 Cr and was applied at rates of 8.8 t ha-1. The leather shavings contained 17.1 g kg-1 and the shreds, 19.4 g kg-1 Cr. These wastes were applied at rates of 4.4 and 3.8 t ha-1, respectively. The Cr6+ (K2Cr2O7) and the cattle manure rates were 100 mg kg-1 and 20 t ha-1, respectively. Tannery sludge plus PK increased the soil pH (5.1 to 5.8), the soil N (1.26 to 1.51 g kg-1), and the soil Ca (4.1 to 5.9 cmolc dm-3) .Wheat, lettuce and radish yields in this treatment were similar to the ones obtained with lime plus NPK. Chromium concentrations in the soil and crops cultivated with tannery sludge varied from 40.7 to 71.2 and from 0.08 to 2.71 mg kg-1, respectively. These values were considered normal. Additions of chrome-tanned leather shavings and finished leather shreds did not decrease the crop yields or change Cr concentrations in soil or plants. Cr6+ applications caused an intoxication of the plants which provoked a yield drop in wheat and lettuce of 91 and 86 %, respectively, in comparison to lime plus NPK. The toxic effect of Cr6+ decreased when cattle manure was added.

Atividade de microrganismos solubilizadores de fosfatos na presença de nitrogênio, ferro, cálcio e potássio

(3) Resumo n A capacidade e o potencial de solubilizaAao de 21†isolados de microrganismos solubilizadores de fosfatos (Bacillus, Pseudomonas, Enterobacteriaceae, Penicillium, Aspergillus e Paecilomyces) fo- ram avaliados em cultivos em meio de cultura Glicose-Extrato de Levedura contendo diferentes fosfatos (Ca, Al ou Fe), na presenAa de fontes de N (peptona, amUnio e nitrato) e teores de Fe, Ca e K. O†crescimento e a atividade solubilizadora variaram em funAao do tipo de microrganismo e dos fatores nutricionais. Em†relaAao ‡s fontes de N, a presenAa de amUnio favoreceu a solubilizaAao em seis isola- dos; destes, trŒs solubilizaram somente nesta fonte. O†nitrato diminuiu a atividade solubilizadora, re- duzindo ou inibindo a solubilizaAao. Para a maioria dos microrganismos, a atividade solubilizadora nao foi afetada pelas variaAies nos teores de ferro. Baixos teores de Ca e K limitaram o crescimento de cinco isolados que apresentam caracterIsticas de amplo crescimento (Aspergillus). Em†dois desses iso- lados, a solubilizaAao de fosfato de Ca foi favorecida. VariaAies na capacidade e no potencial de solubilizaAao dos microrganismos, em resposta ‡s condiAies do meio de cultura, indicam que o proces- so ocorre com eficiŒncia variAEvel ou sugerem a presenAa de diferentes mecanismos de solubilizaAao. Termos para indexaAao: fUsforo, microrganismos do solo, solubilizaAao, nitrato, amUnio. Phosphate solubilizing activity of microorganisms in the presence of nitrogen, iron, calcium and potassium Abstract n Twenty-one isolates of phosphate solubilizing microorganisms (Bacillus, Pseudomonas, Enterobacteriaceae, Penicillium, Aspergillus and Paecilomyces) were evaluated for their solubilizing capacity and potential in broth media (Glucose-Yeast Extract) amended with different types of phos- phates (Ca, Al or Fe), in the presence of N sources (peptone, ammonium and nitrate) as well as concen- trations of Fe, Ca and potassium. Microbial growth and phosphate solubilizing activity varied accord- ing to the microorganism and the nutrient supplied. Ammonium increased solubilization activity of six isolates and three of these solubilized only in this source. Nitrate decreased solubilizing activity and in some instances, completely inhibited solubilization. In general, the solubilizing activity of microbial isolates was not affected by different concentrations of iron. Low concentrations of Ca and K limited the growth of five isolates that characteristically form large colonies (Aspergillus). Solubilization of calcium phosphate was increased by two of these isolates. Variations in the phosphate solubilizing capacity and potential of microorganisms as a response to the conditions in the growth medium indi- cate that the process occurs with variable efficiency or suggest the presence of different mechanisms of solubilization.

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.

Potencial poluidor de rejeitos carboníferos: II- efeitos da recuperação com camadas de solo sobre as plantas e a população microbiana

The landscape recomposition with soil layer and the introduction of plants have been used as an alternative to minimize the environmental impact caused by coal mining. The main concern for this practice is the low avaibility of soil from surface horizons and economic viability, consequently it is basic to determine the minimum soil layer thickness to be disposed on the reject. An experiment was carried out with addition of soil (Paleudult) layers with different thickness disposed on the surface of coal rejects, and in subsurface positions, and soil mixed with rejects, concerning effects on biomass yield of white clover (Trifolium repens L.), corn (Zea mays L.), and oat (Avena strigosa L.) as well as on soil microbial abundance. It was established that a soil layer of 10cm thickness was the minimum necessary for clover and oat growth. Toxic concentrations of heavy metals in plants were not detected. However, soil microbial population represented by bacteria, fungi and actinomyces showed a lower density due to the high acidity that ocurred mainly in subsurface layers.

Potencial poluidor de rejeitos carboníferos. I - Caracterizaçäo química da água de lixiviaçäo

The quality of water, air, soil, vegetation and fauna have been affected by the increasing explotation of coal and consequently increasing of rejects that have been accumulated, causing adverse effects on the environment of a region in Rio Grande do Sul State, Brazil. An experiment was carried out to evaluate the chemical composition of leached water as a consequence of soil layers with different thickness disposed on PVC columns in the surface of coal rejects, in subsurface positions, and soil mixed with rejects. The leachates were collected in 1993, during (Zea mays L.) corn and white clover (Trifolium repens L.) growth; in 1995, before and after oat growth (Avena strigosa L.); and in 1996 after corn growth. Leached water had a high electrical conductivity value because its low pH maintened in solution part of the elements dissolved from the residues. High concentrations of S, Fe, Mn, Zn, Ni and Pb were detected in the leached water that can be considered as a potential pollutant of natural water streams.

Erros potenciais na estimativa da mineralização do nitrogênio do solo

The occurrence of organic N was delermined m experiments on N mineralization in ten soils from Rio Grande do Sul State, Brazil. The incubation-leaching method, with CaCI2 0,01 mol L-1, was used and the leveis of mineral, total and soluble organic nitrogen in the extract measured. Periodic leaching of the soil removed a considerable portion of the soluble organic N and thus underestimating the nitrogen mineralization in the soil.