Herbicide retention by mulching in soybean, under no-tillage system

O objetivo deste trabalho foi avaliar a retenção pela palhada, das misturas imazaquin+pendimethalin e sulfentrazone+metribuzin, aplicadas em pré-emergência, no sistema de plantio direto de soja. Os experimentos foram conduzidos na sede do lAPAR em Londrina-PR, na safra 1998/99, utilizando-se palha de aveia-preta (Avena strigosa) como cobertura morta. O delineamento dos experimentos (em número de dois), foi o de blocos ao acaso com cinco repetições. Os tratamentos foram constituídos pelas doses de herbicidas: zero; 0,5 N; N; 1,5 N e 2 N, sendo N a dose normal recomendada para a cultura (no caso, 150 g/ha de imazaquin + 1200 g/ha de pendimethalin e 350 g/ha de sulfentrazone + 360 g/ha de metribuzin). Utilizou-se a cultivar de soja FT-2000. Os herbicidas foram aplicados com pulverizador de precisão propelido a CO2, munido com barra de seis bicos Teejet Flat Spray em leque, 80.02, distanciados 50 em entre sí, vazão de 200 l/ha. Vinte e quatro horas após a aplicação dos herbicidas, os experimentos receberam 48,3 mm de lâmina de água. No dia seguinte, foram amostrados palha e solo em todas as parcelas para análise cromatográfica de resíduos. ôs resultados mostraram que a lâmina de água promoveu a lixiviação de praticamente todo o imazaquin da palha para o solo, o que não ocorreu com o pendimethalin, que ficou todo retido na palha. O sulfentrazone também foi lixiviado para o solo, sendo que 50% do metribuzin aplicado foi detectado no solo após a chuva. The objective of this trial was to study the mulch retention of the herbicide mixtures imazaquin + pendimethalin and sulfentrazone + metribuzin applied in pre-emergence for soybean under no-tillage system. The experiment was settled in Londrina-PR, Brazil, with black oat (Avena strigosa) mulch. A randomized complete block design was used. The treatrnents comprised the following rates of herbicides: zero, 0.5 N, 1.0 N, 1.5 N and 2.0 N (N=normal rate of the herbicide). ln the present study, N=150 g/ha imazaquin + 1200 g/ha pendimethalin and 350 g/ha sulfentrazone + 360 g/ha metribuzin. After twenty four hours ofherbicide applications, 48.3 mm ofwater was applied in the experiments. ln the next day, samples ofsoil and straw were taken for chromatographic analysis purposes. The results showed that 100% of imazaquin and sulfentrazone leached from the straw to the soil. Approximately 50% of metribuzin and 100% of pendimethalin were retained by the oat straw.

Influence of environmental factors on tenuazonic acid production by Epicoccum sorghinum: An integrative approach of field and laboratory conditions

Sorghum is the fifth most cultivated and consumed grain in the world. However, this grain is frequently contaminated with toxins from fungi. The present study evaluated the effects of environmental factors on tenuazonic acid (TeA) production by Epicoccum sorghinum in the field and in controlled laboratory conditions. In this study, 50 sorghum grain samples were collected from summer and autumn growing seasons and analyzed for TeA contamination using LC-MS/MS. To further understand the ecophysiology of this fungus, an isolated strain of E. sorghinum from the field was investigated for its development and TeA production under controlled environmental conditions in the laboratory. In the ecophysiological investigation, the effects of water activity (0.90, 0.95, 0.99) and temperature (18, 22, 26 and 30?°C) were evaluated on the radial growth, enzymatic production and expression of TAS1, which is the gene involved in TeA production. Results showed that in the field, the summer season presented the highest TeA average level in the grains (587.8??g/kg) compared to level found in the autumn (440.5??g/kg). The ecophysiological investigation confirmed that E. sorghinum produces more actively TeA under environmental conditions simulating the summer season. Optimum growth, maximum TAS1 gene expression, and higher extracellular enzymatic production were observed at 26?°C with a water activity of 0.99. Pearson correlation analyses showed that the production of TeA highly correlates with fungal growth. The present study demonstrates that abiotic factors in a combined approach of field and laboratory conditions will assist in predicting the driving environmental factors that could affect growth of E. sorghinum and TeA production in sorghum grains

Quebra de dormência em sementes de Commelina benghalensis

Com o objetivo de estudar alguns aspectos relacionados à dormência das sementes de trapoeraba (Commelina benghalensis L.), dois experimentos foram conduzidos em condições de laboratório. No primeiro experimento, realizado em 1989, utilizaram-se sementes aéreas e subterrâneas oriundas de Paranavaí-PR e apenas sementes aéreas oriundas de Jaboticabal-SP, todas recém-colhidas, nas modalidades de grandes e pequenas (separadas de acordo com seu peso). Os tratamentos de quebra de dormência foram. escarificação mecânica com lixa; escarificação química com ácido sulfúrico; choque térmico úmido; choque térmico seco, além da testemunha. No segundo experimento, realizado em 1990, utilizaram-se sementes do mesmo lote do experimento anterior, após um ano de armazenamento em câmara a 10o C, sem qualquer tratamento de semente, visando verificar a germinação das sementes. Os resultados indicaram que: 1) o ácido sulfúrico foi o tratamento que proporcionou as maiores porcentagens de germinação (P.G.) e os maiores índices de velocidade de germinação (I.V.G.) em todos os tipos de sementes estudadas; 2) a P.G. e o I.V.G. das sementes recém-colhidas aumentam após um ano de armazenamento; 3) as sementes grandes apresentam maior P.G. e maior I.V.G. que as sementes pequenas; 4) as sementes colhidas em Paranavaí, apresentaram uma tendência de maior P.G. e maior I.V.G. que as colhidas em Jaboticabal.The objective of this work was to study some aspects related to the dormancy of Commelina benghalensis seeds. Two experiments were conducted under laboratory conditions. ln 1989 freshly harvested aerial and underground seeds from Paranavaí, PR, and aerial seeds from Jaboticabal, SP, were divided by their weight into large and small. Except for a control the seeds were subjected to dormancy breaking treatments: mechanical scarification with abrasive paper; chemical action with sulphuric acid; hot water; dry heating. ln 1990 a further experiment, without dormancy breaking treatment, was conducted with seeds from the same lot, after one year in cold storage at 10o C. The results over a 30-day period were: I) sulphuric acid induced the highest germination (P.G.) and the highest speed of germination index (S.G.I.) in all kinds of seeds studied; 2) the P.G. and the S.G.I. of the seeds seem to increase during storage; 3) the larger seeds showed higher P.G. and S.G.I. than the smaller ones; 4) the seeds from Paranavaí showed a tendency of higher values of P.G. and S.G.I. than those from Jaboticabal