Sistemas de manejo de plantas daninhas no desenvolvimento e na produtividade da soja

Abstract

RESUMOA escolha do momento adequado para a dessecação da cobertura vegetal antecedente à semeadura é fundamental para o êxito da cultura da soja cultivada no sistema de plantio direto. Neste contexto, o objetivo do trabalho foi o de avaliar dois sistemas de manejo de plantas daninhas: imediatamente antes da semeadura (sistema "Aplique-Plante" -AP) e o manejo antecipado (MA), composto por duas aplicações. No MA, a primeira aplicação de glyphosate (1240 g ha -1) foi entre 30 e 35 dias antes da semeadura da cultura, e a segunda às vésperas da semeadura. Para o AP, as aplicações com 1.080 a 1.260 g ha -1 de glyphosate foram realizadas 48 horas antes da semeadura. Os trabalhos foram desenvolvidos na safra 2003/2004, em seis localidades no Estado do Paraná: Sertãozinho, Campo Mourão, Iretama, Pitanga, Boa Esperança e Mamborê, em áreas com grande densidade de infestação de plantas daninhas antes da semeadura direta da soja. Foram realizadas avaliações referentes ao controle das plantas daninhas e desenvolvimento e produtividade da cultura. Com a utilização do MA foi proporcionado maior controle das plantas daninhas após a emergência da cultura. As plantas de soja nas áreas AP estavam com menor altura, em comparação às no MA, evidenciando-se atraso no crescimento. Verificou-se redução de produtividade em todas as localidades onde se adotou o manejo AP, com reduções entre 15% e 50%.Palavras-chave: dessecação, Glycine max, plantas daninhas, manejo integrado, semeadura direta. ABSTRACT BURNDOWN SYSTEMS ON GROWTH AND GRAIN YIELD IN SOYBEANS IN PARANÁ STATE, BRAZILThe choice of the adequate moment for the desiccation of the green cover that precedes the sowing is fundamental for the success of no-till soybeans. This context, the work was aimed to study two burndown systems: desiccation immediately before sowing (AP) and anticipated desiccation (MA), composed by two burndown herbicide applications. For MA, the first application of glyphosate (1240 g ha -1) occurred between 30 and 35 days before the sowing of the crop, and the second was done just before sowing. For AP, the applications (1080 to 1260 g ha -1 of glyphosate) occurred within 48 hours prior to sowing. The trials were developed in 2003/2004 growing season, in six localities in Paraná State: Sertãozinho, Campo Mourão, Iretama, Pitanga, Boa Esperança, and Mamborê, in areas with high density of weeds preceding no-till soybean sowing. Evaluations related to weed control and soybean development and grain yield were performed. MA burndown systems provided improved control of weeds after crop emergence. Soybean plants from AP areas were shorter, in comparison to ME, evidencing a delay in the shoot growth. Reduction of grain yield was verified for all localities when AP burndown system was adopted, with reductions between 15% and 50%.Key words: desiccation, Glycine max, weeds, integrated management, no-till.

Corn and soybean yields as affected by cover crops and herbicide timing under no-tillage system

“…This could be associated with the amount of straw on the soil surface, because a large amount of straw can affect plant growth and affect yield and yield components (Monquero et al, 2010;Nascente and Crusciol, 2012;Nascente et al, 2013b). Constantin et al (2009) found that soybeans emerging on soil with a big amount of cover crop biomass had their productivity reduced. They showed that in addition to cover crops shadow, there are other factors such as the demand for nitrogen by the microorganism decomposing straw and allelopathic effects.…”

“…Also Monquero et al (2010) reported that 20 days or more are the best time to desiccate B. brizantha before planting soybeans to avoid yield loss. Constantin et al (2009) and Nascente and Crusciol (2012) suggest that cover crop desiccation should be done with more than 10 days before planting to avoid possible yield reduction caused by the herbicide.…”

“…As B. brizantha is less sensible to glyphosate and take more days to die, it is very important to wait two to three weeks between desiccation and planting of annual crops. Also Constantin et al (2009) reported that it is necessary to have an interval between glyphosate application and corn planting to prevent corn grain loss. This interval can avoid the herbicide remobilization to the corn plants and the possible allelopathic effect of cover crops or nitrogen immobilization, as well as provide rapid and vigorous development of succeeding crops.…”

“…Furthermore, according to Coupland and Lutman (1982) in glyphosate applications near the planting time, there is the possibility of root exudation of herbicides from cover crops to corn or soybean, especially if the roots of cover crops treated with herbicide are numerous and close to the roots of crops. Research showed that the best time to dry out the weeds or cover crops ranges between seven and 20 days before planting soybeans or corn (Constantin et al, 2009;Nunes et al, 2009;Monquero et al, 2010;). …”

Weed Incidence After Soybean Harvest in No-Till and Conventional Tillage Croprotation Systems in Roraima’s Cerrado

“…The competition with weeds is one of the factors that most affect the development and productivity of soybean cultures, since they hinder harvesting and are a shelter for pests and diseases and harmful allelopathic actions, causing a decrease of up to 80% in the culture productivity (Constantin et al, 2009;Correia and Durigan, 2010). The identification of weeds in planting areas allows verifying the qualitative and quantitative differences of the found species (Santos et al, 2016).…”