Sourgrass (Digitaria insularis) is one of the main species causing significant losses in Brazilian soybean production systems. Thus, this paper aimed to evaluate sourgrass interference on soybeans grown under Cerrado conditions. Three field experiments were conducted, of which the first two (E1 and E2) simulated sourgrass after pre-sowing burndown, using plants already emerged by the time soybeans were sown; whereas the third (E3) simulated both sourgrass and soybeans emerged simultaneously. Both E1 and E2 were conducted in a randomized complete block design (RCBD) with five treatments based on sourgrass infestation densities (0, 2, 4, 6, and 8 plants m-2) and four replications. In turn, E3 was also carried out in an RCBD but with treatments arranged in a 2 x 5 factorial and four replications. The first factor comprised two soybean cultivars, while the second was sourgrass density levels, just as in E1 and E2. The results showed that increasing sourgrass densities reduced soybean yield regardless of the plant growth stage when the crop was sown. Yield losses were higher when sourgrass plants were already established by the time soybean was sown. Soybean yield losses reached up to 80% under higher sourgrass infestation levels.
Herbicide management for the control of sourgrass and mission grass and forCongo grass suppression Manejo de herbicidas para o controle de capim-custódio, capim-amargoso e supressão de capim-ruziziensis
The advance of intercropping has generated the need for studies that evaluate methods of suppression of forage grasses in order to not harm the development of the commercial culture. The aim of this study is to evaluate the sensitivity of forage grasses to post-emergence herbicide application. To this end, an experiment was carried out in a greenhouse using a randomized complete block design in a 4 x 9 factorial scheme with four replicates. The first factor consisted of the forage grasses Urochloa ruziziensis, Panicum maximum cv. BRS Tamani, P. maximum cv. BRS Quênia, and P. maximum cv. BRS Zuri. The second factor consisted of the combination of eight herbicide treatments applied at post-emergence in association with atrazine (1200 g a.i. ha -1 ), besides a control treatment, without application. P. maximum cv. BRS Quênia was the least sensitive to post-emergence herbicide application. Tembotrione (42 and 84 g a.i. ha -1 ) and mesotrione (48 and 96 g a.i. ha -1 ) have potential for suppression of U. ruziziensis. Tembotrione (84 g a.i. ha -1 ), glyphosate (200 g a.i. ha -1 ), and nicosulfuron (7.8 g a.i. ha -1 ) have potential for suppression of the cv. BRS Quênia, and tembotrione (42 g a.i. ha -1 ) and mesotrione (96 g a.i. ha -1 ) have potential for the suppression of BRS Tamani. The P. maximum cv. BRS Zuri presented a higher plant height, shoot dry matter, and root dry matter than the other forages evaluated. For this forage, the use of nicosulfuron herbicides at post-emergence, regardless of the dose, reduced the shoot dry matter by 70%.
Soybean-maize succession is the main annual cropping system used in Brazilian cerrado. However, due to water restrictions, the cultivation of maize (off-season crop) is not viable after cultivation of late maturing soybean cultivars and/or when late soybean seeding occurs due adverse weather conditions. In this scenario, the use of cover crops can be a good option to benefit soil health and consequently the soybean yield in the next crop season. The objective is to evaluate the effects of cover crops on biomass inputs, nutrient cycling, and nematode control during the off-season in the Cerrado biome. The study was conducted for three years in two locations in the state of Goiás. We evaluated five options of cover crops after soybean cultivation: 1) Mix of cover crops (Pennisetum glaucum, Crotalaria spectabilis, and Urochloa ruziziensis), 2) P. glaucum, 3) C. spectabilis, 4) U. ruziziensis 5) U. brizantha cv. Marandu, and 6) U. brizantha BRS Paiaguás. The results revealed that Pennisetum glaucum (9633 and 6958 kg ha-1 in Montividiu and Rio Verde) and U. brizantha cv. Marandu (8015 kg ha-1 in Rio Verde) produced the highest amount of biomass on average over three years. The treatments soybean/Crotalaria spectabilis and soybean/Pennisetum glaucum reduce the population of the nematodes. However, the use of a more diversified system such as the mix of cover crops provided a greater soybean yield, soil coverage and a high concentration and release of nutrients during the soybean cycle. Being one important alternative for ensure agricultural sustainability in the Cerrado.
A infestação de capim-amargoso (Digitaria insularis) é responsável por grande parte dasperdas de produtividade em lavouras de soja (Glycine max). Entretanto, pouco se temestudado sobre a interferência desta espécie na produção de grãos para sementes. O objetivodeste estudo foi avaliar a interferência de capim-amargoso sobre a qualidade de sementes desoja. Um experimento foi instalado para estudar cinco densidades de capim-amargoso (0, 2,4, 6 e 8 plantas m-2) em duas cultivares (Garra IPRO® e ST797 IPRO®). Os danos na maiordensidade avaliada (8 plantas m-2) foram de perda de 16% no número de sementes normais,32% a mais de sementes mortas e 16% de perda na germinação para a cultivar ST797IPRO®. A cultivar Garra IPRO® não apresentou diferenças nestas variáveis, sugerindomelhor habilidade competitiva em relação a cultivar ST797 IPRO®. Quanto maior ainfestação de capim-amargoso na soja, maiores as chances de perda na qualidade desementes. O nível de dano às sementes pela presença de capim-amargoso depende dahabilidade competitiva de cada cultivar.
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