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

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.

The search for cultivation practices that provide increased soybean yield has been recurrent. From this context, the objective of this study was to evaluate the agronomic performance of soybeans with the application of phytosanitary products, as well as the effect of 2,4-D amine subdoses on this crop. Two field experiments were conducted in a randomized block design (RCBD), in a factorial arrangement, with four replications. In the first experiment, one factor corresponded to the soybean post-emergence application of propiconazole, 2,4-D amine, lactofen, imazethapyr and Grainset ® , while the other factor corresponded to the single or sequential application of these products. For the second experiment, one factor corresponded to the application of 2,4-D amine at two phenological stages of soybeans: V4 or V8 (4 and 8 fully expanded trifoliate leaves, respectively), while in the other factor the subdoses of this herbicide were evaluated: 4.03, 8.06, 12.09, 16.12, 20, 15 and 24.18 g a.i. ha -1 . In both experiments, the additional treatment consisted of the control without application. 2,4-D amine applied in subdoses has potential for use in soybeans. The application of 2,4-D amine subdoses promotes changes in morphological parameters of this crop. Increase in the yield of this crop can be obtained with the application of 2,4-D amine in subdoses varying between 16.12 and 20.15 g a.i. ha -1 .

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%.

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.

Sourgrass has a high competitive potential, resulting in yield losses of several crops. With the increase of grain sorghum cultivation in the Cerrado, mainly in the second crop, studies are needed to assess the interference of sourgrass on this crop. The objective of this work was to evaluate the interference of increasing densities of sourgrass on the sorghum crop under Cerrado conditions. The field experiment was carried out in a randomized block design, with four replications. Five treatments, composed of densities of 0, 2, 4, 6, and 8 sourgrass plants per m -2 , were evaluated. To simulate the densities of sourgrass, this species was planted in the predecessor crop (soybean) according to the predicted density in each experimental unit, and later, at the time of sowing the sorghum, the sourgrass plants, which were clogged, were cut, in order to simulate the condition provided by mechanized harvesting. During the evaluation of the effect of the treatments on the sorghum crop, the stand and plant height, stalk diameter, panicle length, mass of 100 grains, and yield were measured. The increase in sourgrass density, in coexistence with sorghum, negatively affects all vegetative and reproductive parameters evaluated in the crop. For each sourgrass plant m -2 , in coexistence with sorghum, there was a reduction in yield equivalent to 445 kg ha -1 . The maximum reduction in sorghum yield observed was 87%, in a condition in which the crop was developed in coexistence at the density of 8 sourgrass plants m -2 .