Cotton response to mepiquat chloride and temperature

Gibberellin inhibitor growth regulators are used for cotton (Gossypium hirsutum L.) canopy manipulation to avoid excess growth and yield losses. However, under temperatures below or over the optimum for cotton production the effect of mepiquat chloride (MC) has not always been significant. In this experiment, cotton plants were grown in growth chambers to study the response to MC as affected by temperature and to determine if an increase in dose could overcome the temperature effects. Mepiquat chloride was applied at rates of 0, 15 and 30 g ai ha-1 at the pinhead square stage. Plants were then grown under three temperature regimes: 25/15 °C, 32/22 °C, and 39/29 °C (day/night temperatures) for 51 days. Higher temperatures increased plant height, reproductive branches, fruit number, fruit abscission, and photosynthesis per unit area, but decreased leaf area and chlorophyll. The largest effect of MC on plant height was observed when the daily temperature was 32 °C, with nights of 22 °C, which was also best for plant growth. High temperatures not only decreased the effectiveness of MC on plant height control, but also caused lower dry matter and fruit number per plant. Low temperatures (25/15 ºC) decreased cotton growth and fruit retention, but a higher concentration of MC was required per unit of growth reduction as compared with 32/22 ºC. At high temperatures, the rate of MC to be applied must be disproportionately increased, because either plant growth is impaired by high temperature lessening the effect of MC, or degradation of MC within the plant is too rapid

Soybean potassic fertilization in a Dark-Red Latosol sandy loam

Durante três anos foi conduzido um experimento em Latossolo Vermelho-Escuro fase arenosa, no qual foram estudados os efeitos de adubações anuais com 0,40, 80, 160 e 240 kg/ha de K2O, nas formas de cloreto de potássio e sulfato de potássio, aplicados no sulco de semeadura ou em área total com incorporação. Observou-se resposta à adubação potássica a partir do segundo ano de cultivo. As máximas produções sempre estiveram associadas a teores de potássio nas folhas acima de 1,5%. Em anos mais secos que o normal, as aplicações a lanço proporcionaram melhores resultados do que as aplicações em sulcos. Não foram observadas diferenças entre as fontes de potássio utilizadas. Notou-se acentuado decréscimo nos teores de potássio trocável do solo, com o transcorrer do tempo, sendo necessária a aplicação de doses maiores que 80 kg/ha de K2O por ano para manter o nível original. Por outro lado, a aplicação de doses elevadas de potássio levou a uma perda significativa do nutriente por lixiviação.During three years, an experiment was carried out in a Dark-Red Latosol (sandy loam) to study the effects of annual applications of 0, 40, 80, 160 and 240 kg/ha of K2O as potassium chloride and potassium sulphate, applied in the seed rows or spread and incorporated. There was a yield increase due to potassium fertilization since the second year. Maximum yields were associated to potassium levels in the leaves above 1.5% In drier than normal years, the spreading applications led to better results than row applications. There were no differences between potassium sources. A decrease in exchangeable potassium levels in the soil was observed; for this reason, the application of doses bigger than 80 kg/ha of K2O a year was considered necessary to maintain the original potassium level. On the other hand, the fertilization with higher potassium doses led to a significant loss of potassium by leaching

Efeitos da concorrência de ervas daninhas na produção do sorgo granífero

A field experiment was conducted in a "Terra Roxa Estruturada" (Ultisol, clay), during three years (1978/79, 1979/80 and 1980/81) to study the effects of weeding time and number on yield and yield components of grain sorghum cv. Contiouro. The experimental design was a randomized blocks with the following treatments: 1) free weed competition; 2) weeding at 15 days after seedling emergence (DASE); 3) weeding at 15 and 30 DASE; 4) weedingat 15, 30 and 45 DASE; 5) weeding at 15, 30, 45 and 60 DASE; 6) weeding at 30 and 45 DASE; 7) weeding at 30 and 45 DASE; 8) weeding at 45 DASE. The grain yields of the treatments with weeding did not differ significantly among then, but differed from those treatments in plots free of weeds. When grain sorghum was allowed to grow without weed competition there was an increase in head weight and number of panicles per hectare, resulting in higher yields. One weeding 15 DASE was sufficient to get a grain yield as high as that of the treatment with the greatest number of weedings.O presente estudo foi levado a efeito em um solo classificado como Terra Roxa Estruturada, nos anos agrícolas de 1978/79, 1979/80 e 1980/81, com o objetivo de estudar os efeitos da época de execução de carpas e da competição de ervas daninhas com a cultura do sorgo. O delineamento estatístico foi o de blocos ao acaso, com oito tratamentos: 1) sem carpas; 2) carpa aos 15 dias após a emergência do sorgo (DAES); 3) carpas aos 15 e 30 DAES; 4) carpas aos 15,30 e 45 DAES; 5) carpas aos 15, 30, 45 e 60 DAES; 6) carpas aos 30 DAES; 7) carpas aos 30 e 45 DAES; 8) carpa aos 45 DAES. As produções de grãos dos tratamentos que receberam carpas não diferem entre si significativamente, porém foram superiores às do tratamento que não as recebeu. Quando se permitiu ao sorgo desenvolver-se sem a competição do mato, houve aumento de peso e número de panículas por hectare resultando em maior produção de grãos. Uma carpa efetuada 15 dias após a emergência do sorgo foi suficiente para uma produção equivalente a do tratamento que recebeu maior número de carpas.