The objective of this work was to exclusively improve the management of wastes constituted mainly by organic solvents, due to the opportunities for improvements in the processing of such substances in the institution where the studies were realized. By means of the tests carried out in the distillation system using acetone as a reference, advantages and disadvantages were found with increasing/decreasing the temperature used in the process. From the use of gas chromatography, it was possible to obtain a more precise control of the quality of the recovered product and also to verify the high efficiency of the distillation process in the separation of the solvent from the other contaminants present in the waste. And in terms of comparison of treatments, distillation proved to be environmentally more sustainable and about 8 times more economical than incineration.

Abstract Best fertilizer management practices such as adopting the right N sidedress timing can reduce N losses by volatilization, thus, raising N-fertilizer recovery and grain yield. To evaluate ammonia (N-NH3 ) losses, N-fertilizer recovery and grain yield as a function of urea sidedress timing in corn, a field study was conducted during the 2011-2012 and 2012-2013 growing seasons, adopting a complete randomized block design with four replications. Treatments consisted of urea sidedress timing (140 kg N ha-1) at V4, V6, V8, V10, and V12 growth stages, plus a control without sidedress N. The largest N losses by N-NH3 volatilization occurred when urea was applied at V10 or V12 growth stages, reaching losses of 35 and 41 % of the total applied N. Although climatic factors influences N-NH3 volatilization process, crop characteristics such as canopy development also seems to affect N-NH3 losses. Nitrogen application at V4 or V6 growth stages resulted in greater N-fertilizer recovery from urea sidedress, reaching values of 53 %. No increase in corn grain yield was observed with N application at different corn growth stages during the two growing seasons evaluated, most likely due to high N mineralization rates from the soil.

OBJECTIVE: The 13C-urea breath test is the main non-invasive test for the diagnosis of Helicobacter pylori infection. The availability of this test throughout the country is limited, mainly due to the difficulty in obtaining the labeled isotope from abroad. Recently, researchers from the Nuclear Energy Center in Agriculture at the University of São Paulo (CENA/USP) succeeded in synthesizing 13C-enriched urea for Helicobacter pylori diagnosis. The aim of the study was to compare the performance of the 13C-urea breath test using 13C-urea acquired abroad with that of a test using 13C-urea synthesized in Brazil. METHOD: Sixty-four dyspeptic patients participated in the study (24 men and 40 women). Initially, the patients performed the 13C-urea breath test using the imported substrate (Euriso-Top, France). Seven to fourteen days later, all the patients repeated the test using the Brazilian substrate. The samples from both examinations were processed in an infrared isotope analyzer (IRIS, Wagner Analisen Technik, Germany), and all delta over baseline (DOB) [%] values above four were considered positive results. RESULTS: Twenty-seven patients (42%) exhibited negative results for Helicobacter pylori infection, and thirty-seven patients (58%) exhibited positive results when tested using the foreign substrate (gold standard). There was a 100% concordance regarding the presence or absence of infection when the gold standard results were compared with those obtained using the Brazilian substrate. CONCLUSIONS: Similar performance in the diagnosis of Helicobacter pylori infection was demonstrated when using the 13C-urea breath test with the Brazilian 13C-urea substrate and the test with the substrate produced abroad. This validation represents an important step toward increasing the availability of the 13C-urea breath test throughout the country, which will have a positive influence on the management of Helicobacter pylori infection.

O enxofre tem papel essencial em plantas, sendo um dos principais nutrientes em diversos processos metabólicos; ele apresenta quatro isótopos estáveis (32S, 33S, 34S e 36S), com abundância natural de 95,00, 0,76, 4,22 e 0,014 % em átomos, respectivamente. Desenvolver um método para determinação isotópica do S por espectrometria de massas de razão isotópica (IRMS) em amostras de solo foi o objetivo deste trabalho. A oxidação de S orgânico a sulfato (S-SO4(2-)) foi avaliada utilizando a oxidação via seca com agentes oxidantes alcalinos. A concentração S-SO4(2-) foi determinada pelo método turbidimétrico, e os resultados mostraram que o processo de conversão foi adequado. A obtenção do gás SO2 foi por decomposição térmica do BaSO4 em uma linha de vácuo a 900 ºC, em presença de NaPO3. A determinação isotópica do S (% em átomos de 34S) foi realizada em um espectrômetro de massa (IRMS). Neste trabalho, a utilização de material marcado (K2(34)SO4) teve como propósito validar o método para determinação isotópica do S; os resultados obtidos foram exatos e precisos, mostrando a viabilidade do método proposto.

Sulphur plays an essential role in plants and is one of the main nutrients in several metabolic processes. It has four stable isotopes (32S, 33S, 34S, and 36S) with a natural abundance of 95.00, 0.76, 4.22, and 0.014 in atom %, respectively. A method for isotopic determination of S by isotope-ratio mass spectrometry (IRMS) in soil samples is proposed. The procedure involves the oxidation of organic S to sulphate (S-SO4(2-)), which was determined by dry combustion with alkaline oxidizing agents. The total S-SO4(2-) concentration was determined by turbidimetry and the results showed that the conversion process was adequate. To produce gaseous SO2 gas, BaSO4 was thermally decomposed in a vacuum system at 900 ºC in the presence of NaPO3. The isotope determination of S (atom % 34S atoms) was carried out by isotope ratio mass spectrometry (IRMS). In this work, the labeled material (K2(34)SO4) was used to validate the method of isotopic determination of S; the results were precise and accurate, showing the viability of the proposed method.

The sulphur take an essential role in plants and it is one of the main nutrients in several metabolic processes. The dry ash oxidation, using alkaline oxidizers agent, is the simplest and most economical form for the oxidation of Organic S to sulfate in plants. The objective of this work is to propose a method for sulfur determination in plants samples using dry ash oxidation and agent oxidizers alkaline. The quantification of S-SO4(2-) in samples was accomplished by turbidimetric method. The results demonstrated that the proposed method for oxidation alkaline was appropriate.

O glifosato é o herbicida de maior participação no mercado mundial, sendo utilizado intensivamente na agricultura há mais de 30 anos, principalmente devido ao custo relativamente baixo e à alta eficiência sobre diferentes espécies. Descreve-se um método para a síntese do glifosato na forma do sal isopropilamina enriquecido no isótopo estável do nitrogênio (15N). A síntese do herbicida-15N foi realizada utilizando-se da reação de fosfometilação com diaquil fosfito e glicina-15N. Os testes foram realizados em microescala e em quantidades equimolares. Foi possível obter um rendimento de 20%. Para testar a eficiência do glifosato sintetizado, realizou-se experimento em câmara de crescimento com a planta daninha Lolium multiflorum (azevém), a qual é eficazmente controlada segundo à bula dos produtos a base do sal de isopropilamina (glifosato). O delineamento experimental foi inteiramente casualizado, com quatro repetições, sendo os tratamentos provenientes de fontes de sal de isopropilamina na dose comercial recomendada do produto (720 g i.a. ha-1). Avaliou-se a produção de fitomassa fresca e seca, da parte aérea e radicular, aos 21 dias após a aplicação (DAA), e a toxicidade dos tratamentos aos 7, 14 e 21 DAA. As fontes de sal de isopropilamina empregados não diferiram, o que deverá permitir sua utilização como traçador isotópico.

Glyphosate is the herbicide with the greatest participation in the world market, and it has been used intensively in agriculture for over 30 years, especially because of its relatively low cost and high effectiveness on different species. This study describes a synthesis method of glyphosate in the form of the isopropylamine salt enriched in the stable nitrogen isotope (15N). The 15N-herbicide synthesis was performed using a phosphomethylation reaction with dialkyl phosphite and 15N-glycine. The tests were conducted at a microscale and equimolar quantities. A 20% yield was obtained at the established conditions. To test the effectiveness of the synthesized glyphosate, an experiment was performed in a growth chamber with the weed Lolium multiflorum (ryegrass), which is mentioned to be effectively controlled as indicated in package inserts ofisopropylamine salt-based products (glyphosate). The experimental design was completely randomized, with four replicates, and treatments consisted of isopropylamine salt sources at the commercial dose recommended for the product (720 g a.i. ha-1). The production of green and dry phytomass of the above-ground part and roots was evaluated 21 days after application (DAA), and the treatment toxicity was evaluated 7, 14, and 21 DAA. The isopropylamine salt sources did not differ, recognizing them as useful isotopic tracers.

O S no solo pode ocorrer como S-orgânico e S-inorgânico, sendo a forma orgânica responsável por 95 % do S na maioria dos solos. A eficiência da oxidação do S-orgânico a sulfato, na determinação de S-total em amostras de solo, foi avaliada com o emprego de métodos de oxidação por via úmida (ácida) e via seca (alcalina). Com o propósito de avaliar o método por via úmida e possivelmente empregá-lo como referência na avaliação do método por via seca, proposto no presente trabalho, fez-se uso de um padrão de referência da National Institute of Standards Tecnology (NIST), Montana Soil (NIST 2710). A oxidação por via seca com agentes oxidantes alcalinos é um dos métodos mais simples para oxidação de S-orgânico à forma de sulfato e foi comparado com o método por via úmida. O objetivo deste trabalho foi desenvolver um método de fácil execução que possibilite a determinação do elemento (S-total) em amostras de solo por turbidimetria. A avaliação da eficiência da oxidação do S-orgânico a sulfato foi realizada com três misturas oxidantes alcalinas: NaHCO3 + Ag2O, mistura Eschka (17 % de Na2CO3, 66 % de MgO e 17 % de K2CO3) e NaHCO3 + CuO. O procedimento na quantificação da concentração de sulfato foi baseado na reação com cloreto de bário e detecção por turbidimetria. A quantificação do S na amostra-padrão, pelo uso do método por via úmida, mostrou-se adequada com boa precisão e exatidão. Deve-se ainda destacar que não foram encontradas diferenças significativas (confiabilidade de 95 %) entre os métodos por via úmida e via seca (mistura oxidante de NaHCO3 e Ag2O) em seis diferentes solos brasileiros, o que possibilita o uso do método proposto por via seca no preparo de amostras de solos para determinação de S total.

Sulfur in the soil occurs in two basic forms, organic and inorganic S. The organic form accounts for 95 % of S in most soils. The effectiveness of organic S to oxidate to sulfate was evaluated for total S determination in soil samples by wet (acid) and dry-ash (alkaline) oxidation methods. To evaluate the wet method and the possible use as a reference when evaluating the dry method proposed here, a reference standard from the US National Institute of Standards and Technology (NIST) was used (Montana Soil - NIST 2710). The dry-ash oxidation process with alkaline oxidizing agents is one of the simplest oxidation methods of organic S to the sulfate form and was compared with the wet process. The objective of the study was to develop a dry method that would be easy to apply and allow the complete conversion of organic S to sulfate in soil samples and later detection by turbidimetry. The effectiveness of organic S oxidation to sulfate was evaluated by means of three alkaline oxidation mixtures: NaHCO3 + Ag2O, Eschka mixture (17 % Na2CO3, 66 % MgO, and 17 % K2CO3), and NaHCO3 + CuO. The procedure to quantify the sulfate concentration was based on the reaction with barium chloride and turbidimetric detection. Sulfur quantification in the standard sample by the wet method proved adequate, precise and accurate. It should also be pointed out that no significant differences were found (95 % reliability) between the wet and dry processes (NaHCO3 and Ag2O oxidation mixture) in six different Brazilian soils. The proposed dry method can therefore be used in the preparation of soil samples for total S determination.

O superfosfato simples é um dos fertilizantes mais utilizados atualmente como fonte de fósforo e uma alternativa para enxofre. O enxofre apresenta quatro isótopos estáveis, 32S, 33S, 34S e 36S, com abundância natural de 95,00; 0,76; 4,22 e 0,014% em átomos, respectivamente. O superfosfato simples marcado com 34S foi obtido a partir da reação química em proporção estequiométrica entre o Ca(H2PO4)2 e o Ca34SO4.2H2O. O Ca34SO4.2H2O foi enriquecido com 5,85 ± 0,01% em átomos de 34S. O Ca(H2PO4)2 foi obtido a partir da reação entre CaCl2.2H2O com o H3PO4. A decomposição térmica do superfosfato marcado para produção do 34SO2 gasoso foi realizada em linha de vácuo a 900ºC na presença de NaPO3. A determinação isotópica do S (% em átomos de 34S) foi realizada no espectrômetro de massas. O rendimento da produção do Ca(H2PO4)2 e do superfosfato simples marcado foi em média 97 e 99%, respectivamente, e a pureza do superfosfato marcado foi estimada como 96%. Não foi observado fracionamento isotópico no processo de produção do superfosfato simples marcado com 34S.

Single superphosphate is currently one of the mostly used fertilizers as an alternative source for phosphorus and sulphur. Sulphur presents four stable isotopes (32S, 33S, 34S, and 36S) with natural abundances of 95.00; 0.76; 4.22; and 0.014% in atoms, respectively. Single superphosphate labeled with the 34S isotope was obtained from a chemical reaction in stoichiometric amounts between Ca(H2PO4)2 and Ca34SO4.2H2O. Calcium sulphate (Ca34SO4.2H2O) was enriched with 5.85 ± 0.01 atoms % of 34S. The Ca(H2PO4)2 reagent was obtained from a reaction between CaCl2.2H2O and H3PO4. The reaction between the Ca(H2PO4)2 thus produced and the labeled Ca34SO4.2H2O compound was then performed to obtain the 34S-labeled single surperphosphate. The thermal decomposition of the labeled superphosphate for the production of gaseous 34SO2 was carried out under a vacuum line at 900ºC in the presence of NaPO3. The isotopic determination of S (atoms % of 34S) was carried out on an ATLAS-MAT model CH-4 mass spectrometer. The production yield of Ca(H2PO4)2 and labeled single superphosphate were approximately 97 and 99% respectively, and the purity level of the labeled single superphosphate was estimated as 96%. No isotopic fractionation was observed in the production process of 34S-labeled single superphosphate.

In this paper, we present procedures for the treatment and final disposal of residual solutions containing chromium, in order to evaluate the effectiveness of chemical precipitation of the metal and the potential of the glass encapsulation technique, using broken laboratory glassware. The results demonstrated that pH-values convenient for chemical precipitation are between 10 - 11. With regard to Cr(OH)3 encapsulation, the leaching and solubilization tests allowed to classify the waste as non-dangerous and non-inert. Finally, it is pointed out that the adoption of waste management practices in universities should be encouraged, helping to train professionals skilled in good laboratory practices.

Com o emprego dos isótopos do carbono (12C, 13C, 14C) da matéria orgânica do solo (MOS) e das plantas, é apresentado um estudo comparativo entre perfis orgânicos de solos formados em depressões de áreas cobertas por ecossistemas de campos e florestas ao sul do estado do Amazonas, visando o entendimento da dinâmica da paleovegetação. A dinâmica da vegetação atual na região foi avaliada utilizando-se estudos fitossociológicos e caracterizações botânica e isotópica (delta13C) das espécies de plantas presentes em duas bordas floresta-campo. Teores de carbono orgânico total foram superiores nas camadas superficiais no campo, quando comparados com a floresta. Dados de delta13C associados à cronologia do 14C indicaram predomínio de plantas C3 no início do Holoceno em ambos os ecótonos. Entre aproximadamente 7.000-3.000 anos AP verificou-se a influência crescente de plantas C4, indicando regressão da floresta com possível presença de um clima mais seco. A partir de aproximadamente 3.000 anos AP os dados sugeriram expansão da floresta provavelmente relacionada ao retorno a um clima mais úmido. A presença de algumas espécies características da borda, como a Sclerolobium paniculatum e Himatanthus sucuuba, nos campos, sugere o atual avanço da floresta sobre os mesmos. Estas espécies estariam sendo as bioindicadoras desse avanço.

This paper presents a comparative study between organic soil horizons formed in depressions located at the forest/savanna boundary in the Southern Amazon Basin. The influence of the paleovegetation dynamics, based on carbon isotope (12C, 13C and 14C) data of soil organic matter (SOM) and plants was evaluated, as well as the present vegetation dynamics, inferred from the modern vegetation structure, composition and phytosociology. The uppermost soil horizon in savanna showed higher total carbon content than in forest. 13C and 14C data from soil samples indicated a predominance of C3 plants in the early Holocene. About 7000 to 3000 14C yr BP the influence of C4 plants increased, indicating savanna expansion probably related to a drier climate in the region. Since approximately 3000 14C yr BP, the carbon isotope data suggest the expansion of forest probably due to a wetter climate. The presence of typical boundary plant species (Sclerolobium paniculatum and Himatanthus sucuuba) in the savanna also suggested present forest expansion.

O gesso agrícola (CaSO4.2H2O) destaca-se como fonte eficiente de cálcio e enxofre e na redução da saturação de alumínio no solo. O 34S como traçador isotópico pode elucidar aspectos importantes no ciclo do enxofre. Para tanto o Ca34SO4.2H2O foi obtido por reação química entre o Ca(OH)2 e solução de H2(34)SO4, realizada sob agitação lenta. O ácido foi produzido por cromatografia de troca iônica, utilizando resina catiônica Dowex 50WX8 e solução eluente de Na2(34)SO4. Após a precipitação foi separado o precipitado e realizada a secagem em estufa ventilada à temperatura de 60ºC. Nos testes, a partir de 2,2 L de H2SO4 0,2 mol L-1 e 33,6 g de Ca(OH)2, foram produzidos em média 73,7 ± 0,6 g de Ca34SO4.2H2O representando um rendimento médio de 94,6 ± 0,8%, com pureza de 98%. A partir do Ca34SO4.2H2O na presença de NaPO3, em linha de alto vácuo, obteve-se o gás 34SO2 utilizado para a determinação isotópica do S no espectrômetro de massas ATLAS-MAT modelo CH-4.

Agricultural gypsum (CaSO4.2H2O) stands out as an effective source of calcium and sulfur, and to control aluminum saturation in the soil. Labeled as 34S it can elucidate important aspects of the sulfur cycle. Ca34SO4.2H2O was obtained by chemical reaction between Ca(OH)2 and H2(34)SO4, performed under slow agitation. The acid was produced by ion exchange chromatography using the Dowex 50WX8 cation exchange resin and a Na2(34)SO4 eluting solution. After precipitation, the precipitate was separated and dried in a ventilated oven at 60ºC. From 2.2 L H2SO4 0.2 mol L-1 and 33.6 g Ca(OH)2, 73.7 ± 0.6 g Ca34SO4.2H2O were produced on average in the tests, representing a mean yield of 94.6 ± 0.8%, with 98% purity. The 34SO2 gas was obtained from Ca34SO4.2H2O in the presence of NaPO3 in a high vacuum line and was used for the isotopic determination of S in an ATLAS-MAT model CH-4 mass spectrometer.

Programas de Gerenciamento de Resíduos Químicos Laboratoriais vêm sendo implantados em várias universidades do país e do mundo, em reconhecimento à necessidade premente de alterar a realidade de descaso para com o ambiente, associado à responsabilidade objetiva do gerador e, principalmente, à consciência de sustentabilidade, em consonância com a Agenda 21. Neste contexto, o presente trabalho relata essa problemática de forma a reunir uma série de informações por meio de revisão da literatura recente, desenvolvendo uma análise crítica e desmistificando alguns (pré) conceitos através de um questionário aplicado aos pesquisadores atuantes nesta área de conhecimento. Esse estudo permitiu, por fim, a proposição de regras básicas a serem adotadas na implementação de um programa de gerenciamento de resíduos laboratoriais.

Laboratory Waste Management Programs have been established in several universities all over the world. These programs are important because they provide the understanding and protection of the environment, encouraging the waste generator's responsibility and, mainly, accomplishing sustainable practice in the laboratory, in accordance with the Agenda 21. In this context, based on a literature review, the present work discusses the subject, introducing some recommendations to be applied in universities. A questionnaire applied to researchers of this area shows important information about the start of the programs, mainly difficulties, among other cares. This study allowed the proposition of basic rules about the establishment of laboratory waste management.

The aim of this work is to establish a program for the treatment of chemical residues and waste waters at the Centro de Energia Nuclear na Agricultura (CENA/USP), for environmental preservation and training of staff. Five tons of stored residues and the ones currently generated in the laboratories have to be treated. Rational use of water is also part of the program. The traditional purification by distillation has been replaced by purification with ion exchange resins. Lower energy consumption and better water quality were achieved.

Sulfato de amônio (SA) e uréia (U) marcados com 15N foram aplicados na cultura do milho, em sucessão à aveia preta (Avena strigosa Schieb.), no sistema plantio direto, 43 dias antes e 31 dias depois da semeadura, na dose de 80 kg ha-1 de N, incorporados a 5-7 cm de profundidade, em sulcos espaçados de 0,8 m, nas entrelinhas do milho. O objetivo foi quantificar o N dos fertilizantes imobilizado no solo (15N-orgânico), no sulco de adubação, e o N-recuperado na planta nos estádios de 5-6 folhas, 11-12 folhas, florescimento e maturação fisiológica. O delineamento experimental foi inteiramente casualizado com parcelas subdivididas e três repetições. As parcelas foram constituídas das fontes U e SA, e as subparcelas, das épocas de aplicação de N. O experimento foi realizado em Latossolo Vermelho ácrico típico fase cerrado subcadocifólio, na Fazenda Floresta do Lobo-Pinusplan, em Uberlândia (MG). Na aplicação em pré-semeadura, a máxima imobilização foi observada aos 19 dias da aplicação do SA (13,3 kg ha-1 ou 16,6 % do N-aplicado) e aos 40 dias da aplicação da U (13,7 kg ha-1 ou 17,1 % do N-aplicado). A maior quantidade de N fertilizante assimilado pela planta ocorreu entre os estádios de 5-6 e 11-12 folhas (44,1 e 23,4 % do N-SA e N-U, respectivamente). Na aplicação em cobertura, a imobilização do N-SA foi inferior a 3,5 % do N-aplicado, enquanto a imobilização do N-U foi de 9,9 kg ha-1 e 7,9 kg ha-1, respectivamente, nos estádios de 11-12 folhas e florescimento. Até o estádio de maturação fisiológica da cultura, 61,8 % do N-SA e 42,0 % do N-U foram recuperados pelo milho. Em média, nos estádios de 11-12 folhas e de florescimento, para cada kg de N-SA imobilizado, as plantas de milho recuperaram 8,0 e 16,7 kg ha-1 de N fertilizante em pré-semeadura e cobertura, respectivamente. Nos tratamentos com U, a média foi de 3,1 kg ha-1, independentemente da época de aplicação. As produtividades de grãos obtidas com SA e U, independentemente da época de aplicação, foram de 7.824 kg ha-1 e 6.977 kg ha-1, respectivamente. Na adubação em pré-semeadura do milho, o SA apresentou maior rapidez na ciclagem do N imobilizado-mineralizado ("turnover"), em relação a U, e, conseqüentemente, causou maior assimilação do N pela cultura. Em cobertura, no sulco de adubação, somente houve imobilização do N-U, retardando a sua assimilação pela planta.

In order to evaluate the amount of immobilized N and the amount of N-fertilizer recovered by corn plants at the stages:5-6 leaves, 11-12 leaves, flowering, and physiologic maturation, ammonium sulfate (AS) and urea (U), labeled with 15N, were applied to maize in a no-till system 43 days before planting and 31 days after planting at a single rate of 80 kg ha-1 of N incorporated at 5-7 cm depth and in a spacing of 0.8 m. Corn was sown after black oat (Avena strigosa Schieb.). The treatments were applied in split-plots set up in the completely randomized design with three replications. The original plots with two N sources were halved for the application time factor (pre-planting and top-dressing application). The field experiment was carried out on a Typic Acrustox on the farm Floresta do Lobo, Uberlandia, state of Minas Gerais. Results show that in pre-planting application treatments the maximum N-AS immobilization occurred 19 days after the fertilizer application (13.3 kg ha-1 or 16.6 % of N applied) whereas the maximum immobilization of N-U occurred 40 days after fertilizer application (13.7 kg ha-1 or 17.1 % of N applied). The highest amount of 15N-fertilizer taken up by corn plants was observed between the stages 5-6 leaves and 11-12 leaves, at ratios of 44.1 % of N-AS and 23.4 % of N-U. The immobilized N in the treatment with top-dressed AS was lower than 3.5 % of the applied N whereas in the treatment with top-dressed U it was 9.9 kg ha-1 and 7.9 kg ha-1 at the stages 11-12 leaves and flowering, respectively. The recovery of N-fertilizer measured at the stage of physiologic maturation in the treatments with AS and U was 61.8 % and 42.0 % respectively. The 15N-fertilizer amounts recovered by corn plants per kg of 15N immobilized in the treatments with AS were 8.0 kg ha-1 and 16.7 kg ha-1 respectively for pre-planting and top-dressing application. Independent of the application time, the ratio N-fertilizer recovery/immobilized N-fertilizer in the U treatments was 3.1 kg ha-1. The highest corn yields were obtained in the AS treatments (grain mean of 7,824 kg ha-1), independent of the application time. The average crop yield in the treatments with U in both application periods was 6,977 kg ha-1. These results show that when the fertilizers were applied at pre-planting the immobilization-mineralization turnover was faster in the AS than in the U treatment. Consequently, the N-assimilation by corn plants was higher in the AS treatments. For top-dressing application, only U was significantly immobilized.

The purpose of this work was the production of ammonium sulfate double labeled with 15N and 34S ((15NH4)2(34)SO4)), employing the ion exchange technique in two different processes. The first one was carried out using Na2(34)SO4 and (15NH4)2SO4 previously enriched. It was possible to obtain about 54g of (15NH4)2(34)SO4 from 70.0g of Na2(34)SO4 and 64.2g of (15NH4)2SO4 . The second method involved the production of H2(34)SO4, by ion exchange, and its subsequent reaction with 15NH3(aq), using a distillation system, to yield 58 g of (15NH4)2(34)SO4 from 43.1 g of H2(34)SO4.