Profundidade de amostragem do solo para avaliação do enxofre disponível em pomar de limão siciliano (Citrus limon Burm.)

On a medium-textured Dark-Red Latosol (Typic Hapludox), in which increasing levels of sulfate were established by the application of different rates of phosphogypstim (0, 1, 2 e 4 t/ha), a study was carried out to obtain information about the depth of soil samples collected in order to evaluate the S-SO4-2 availability for the Sicilian lemon (Citrus limon Burm.) grafted on "Volkameriano" rootstocks. Sulfate contents at different depths (0-5, 5-10, 10-20, 20-40, 40-80 and 80-120 cm) were determined, by using the NH4OAc 0,5 M in HOAc 0,25 M extractor, 6,12 and 24 months after phosphogypsum application. Sulphur content in the leaves of the lemon plants were also determined at the same dates. Analytical data obtained and the correlation studies that followed, showed that the Sicilian lemon extracted sulphur mainly from the layer 0-20 cm and, therefore, this layer is considered representative for soil sample collection, with the purpose of estimating the available sulphur for Sicilian lemon trees.Em um Latossolo Vermelho Escuro, textura média, no qual foram estabelecidos diferentes teores de enxofre, através da aplicação de doses crescentes de gesso agrícola (0, 1, 2 e 4 t/ha), estudou-se a profundidade adequada para coleta de amostras de terra para avaliação do S-SO4-2 "disponível" para o limão siciliano (Citrus limon Burm.) enxertado sobre porta enxerto Volkameriano. As quantidades de sulfato no solo, extraídas pelo NH4OAc 0,5 M em HOAc 0,25 M, foram determinadas aos 6, 12 e 24 meses após a aplicação do produto nas seguintes profundidades: 0-5, 5-10, 10-20, 20-40, 40-80 e 80-120 cm. As quantidades de enxofre nas folhas do limão siciliano foram também determinadas na mesma época. Os dados obtidos e os estudos de correlação que se seguiram demonstraram evidências de que o limão siciliano teria, no período considerado, extraído enxofre, principalmente, da camada de O a 20 cm de profundidade, e assim sendo, fornece indícios de que esta deve ser a camada amostrada para fins da avaliação deste importante elemento nesta cultura

Controle das perdas de amônia durante a compostagem de estercos com adição de fosfogesso e superfosfato simples

With the purpose of evaluating the effectiveness of phosphogypsum and simple superphosphate in controlling ammonia losses by volatilization during the process of manure composting, an experiment was carried out in closed flasks of 1.6 liter, in which different rates (50, 100, 150 and 200 kg.t-1) of phosphogypsum and simple superphosphate were mixed with a substrate composed of equal amounts (on weight basis) of fresh chicken manure and cattle manure. Ammonia lost by volatilization was determined after 7, 14, 21, 28 and 35 days by trapping the gas in sulfuric acid solution placed in a small glass vial which, in turn, was maintained inside the volatilization flask The remaining acid after the exposure to ammonia was determined by titration with 0.025N NaOH. The amount of ammonia lost by volatilization from the samples decreased with the addition of both products, but for all rates applied, phosphogypsum was more efficient than simple superphosphate. The reduction in volatilization increased with the rate of application of both additives. There was an evidence that the reduction of ammonia loss was due to the presence of gypsum in the additives.Com o propósito de avaliar a eficiência do gesso agrícola e do superfosfato simples em controlar as perdas de amônia por volatilização durante o processo de compostagem de estéreos, foi conduzido um experimento em frascos de vidro fechados de 1,6 litro de capacidade, nos quais diferentes quantidades (50, 100, 150 e 200 kg.t-1) daqueles materiais foram misturadas com um substrato composto de uma mistura de partes iguais (em massa) de estéreos frescos de galinha e de bovino. A amônia perdida por volatilização foi determinada após 7, 14, 21, 28 e 35 dias, coletando-se o gás em solução de ácido sulfúrico encerrada em pequeno recipiente o qual era, por sua vez, colocado no interior do frasco. O ácido remanescente após o período de exposição à amônia era determinado por titulação com solução de NaOH 0,025N. A quantidade de amônia perdida do estéreo por volatilização diminuiu com a adição de ambos os materiais estudados, mas para todas as doses aplicadas o gesso agrícola foi mais eficiente do que o superfosfato simples. Os decréscimos da volatilização foram tanto maiores quanto mais elevadas eram as doses de ambos os aditivos. Houve evidências de que a redução das perdas de amônia deveu-se à presença do gesso nos materiais estudados

Rhizosphere pH and phosphorus forms in an Oxisol cultivated with soybean, brachiaria grass, millet and sorghum

Plants have shown different responses to fertilization with rock phosphate, including responses through alteration of the attributes of rhizospheric soil. The objective of this study was to evaluate soil pH alterations and alterations in the contents of forms of phosphorus in the rhizosphere of soil fertilized with rock phosphate as a result of cultivation of species of plants. An experiment was developed under greenhouse conditions to evaluate alterations in the pH and in the forms of phosphorus in the rhizosphere of an Oxisol fertilized with rock phosphate and cultivated with four species. Treatments consisted of the cultivation of four species of soybean - Glycine max (L.) Merrill, brachiaria grass - Brachiaria brizantha Hochst Stapf, millet - Pennisetum glaucum (L.) R. Brown, and sorghum - Sorghum bicolor (L.) Moench grown in PVC columns filled with soil and divided with a nylon screen (25 µm mesh) to impede root growth in part of the column. After 45 days of cultivation, the soil was divided into the layers of 0-1, 1-2, 2-3, 3-4, 4-5, 5-7, 7-9, and 9-14 mm from the rhizoplane and air dried to determine pH and P contents through Hedley fractionation. In the 1-2 and 2-3 mm layers, soybean cultivation caused an increase in pH when compared to the control treatment (without plants). In the other layers, there were no alterations in pH due to cultivation of plants. The cultivation of millet, brachiaria grass, and sorghum reduced the inorganic P content in the most labile forms only in the 0-1 mm layer from the rhizoplane