A.C. Silva

Mapas de infestação de plantas daninhas em diferentes Sistemas de colheita da cana-de-açúcar

The objective of this work was to identify the differences between the seedbank of a sugarcane field harvested mechanically and a that of a burned sugarcane field, using precision agriculture techniques. The soil sampling for seedbank determination were performed using a 2 ha regular sampling grid. The weed infestation maps were obtained by the kriging interpolation technique. The green sugarcane field presented lower weed infestation potential compared to the burnt sugarcane field, specially the monocotyledonous species. However, some dicotyledonous species can be selected, such as the Ipomoea. It was concluded that precision agriculture can be useful tool for determination of weed infestation maps and that sugarcane straw can be used as a suppression factor for various species.

Análise de crescimento de Brachiaria brizantha submetida a doses reduzidas de fluazifop-p-butil

The objective of this work was to evaluate Brachiaria brizantha cv. MG5 growth under reduced rates of fluazifop-p-butyl to allow its intercropping with soybean. The effects of three doses of the herbicide (0, 18,75 and 37.50 g ha-1) on B. brizantha growth were evaluated in eight timings (14, 18, 28, 35, 42, 49, 56 and 70 days after emergence - DAE). The experiment was arranged in a completely randomized design, with four replications. At each timing, the plants were harvested and the biomass of the leaves, stem, roots and leaf area was obtained. Absolute growth rate, relative growth rate, net assimilation rate, leaf area ratio, specific leaf area, stem and leaf weight ratio were calculated using dry biomass and leaf area data. B. brizantha had suppressed the apical dominance by reduced rates of fluazifop-p-butyl inducing greater tillering. The stems presented greater total biomass and stem length was reduced in the plants treated with the herbicide. The plants treated with fluazifop-p-butyl had thinner leaves, reduced leaf area and absolute growth rate, showing that it is possible to use reduced doses of fluazifop-p-butyl only to reduce B. brizantha growth.

Potencial de lixiviação de herbicidas no solo submetidos a diferentes simulações de precipitação

The objective of this work was to evaluate the influence of rainfall on leaching of herbicides recommended for sugarcane crop in Dystrophic Red Latosol. The experiment consisted in spraying trifloxysulfuron-sodium + ametryn (1463 + 37 g ha-1), imazapic (84 g ha-1), imazapyr (200 g ha-1), 1diuron + hexazinone (1170 + 330 g ha-1) and 2diuron + hexazinone (1330 + 160 g ha-1) on top of PVC columns filled with soil. After spraying, simulated rainfall of 20, 40 and 80 mm was applied on top of the columns. Cucumis sativus (cucumber) was used in bioassays to detect herbicide leaching, with evaluations accomplished 14 and 21 days after application of the treatments. After a 20 mm rainfall simulation, it was verified that the trifloxysulfuron-sodim + ametrin mixtures caused decreasing symptoms of toxicity in the 0 to 20 cm plantules, while the other herbicides had an effect up to 10 cm. The 40 mm rainfall made the mixtures1,2 diuron + hexazinone cause severe symptoms in the cucumber plants at 15 cm depth and decreasing symptoms at depths of 20 cm (formulation 2) and 25 cm (formulation 1). The herbicides trifloxysulfurom sodium + ametryn and imazapyr were detected up to 20 cm of depth. The herbicide imazapic caused toxicity up to 15 cm of depth. At 80 mm rainfall, 1diuron + hexazinone caused toxicity up to 30 cm and 2diuron + hexazinone, imazapyr, trifloxysulfuron sodium + ametryn and imazapic presented toxicity up to 25 cm of depth. It was concluded that all the herbicides evaluated tend to be leached under the influence of rainfall or artificial irrigations.

Eficiência de herbicidas pré-emergentes após períodos de seca

This work aimed to study the effectiveness of pre-emerging herbicides after drought periods in two soil types. Two simultaneous experiments were carried out under greenhouse conditions: in the first, the herbicides (trifloxysulfuron-sodium + ametryn - 351 + 99 g ha-1) + (diuron + hexazinone - 1097 + 27,77 g ha-1), trifloxysulfuron-sodium + ametryn - 1463 + 37 g ha-1, diuron + hexazinone - 1170 + 330 g ha-1, imazapyr 200 g ha-1 and imazapic - 122,5 g ha-1 were applied in vases containing samples of Dystroferric Red Latosol (clay texture); in the second, the doses were adjusted in function of the organic matter and clay level of the soil and applied in vases with samples of Distrophic Red Latosol (medium texture). In each experiment, the species Cucumis sativus and Sorghum bicolor were used as bioindicators and 6 drought periods after herbicide applications (0, 10, 20, 40, 60 and 90 days), with four replicates. Intoxication symptoms were observed on the 7, 14 and 21 days after the bio indicators were sown. The herbicides presented greater stability, i.e. greater toxic effects on the bioindicators along the time on soil with higher clay level and organic matter; isoxaflutole and the mixtures (trifloxysulfuron-sodium + ametryn) + (diuron + hexazinone), and diuron + hexazinone showed greater residual effect in both soils affecting the bioindicators100%.

Acúmulo de macro e micronutrientes por soja e Brachiaria brizantha emergida em diferentes épocas

A rotacao entre soja e B. brizantha tem sido muito utilizada na integracao agricultura-pecuaria. Contudo, o banco de sementes formado pela pastagem anterior torna a forrageira uma especie daninha importante no cultivo da soja. Objetivou-se neste trabalho avaliar os efeitos de diferentes epocas de emergencia de B. brizantha em relacao a soja no acumulo de macro e micronutrientes por ambas as especies. O experimento foi realizado em casa de vegetacao, avaliando-se sete epocas de emergencia de B. brizantha em relacao a emergencia da soja, sendo: -21, -14 e -7 dias, as epocas da emergencia da braquiaria antes da emergencia da soja (DA); 0, a emergencia simultânea da soja e da braquiaria; e 7, 14 e 21 dias, as epocas de emergencia da braquiaria depois da soja (DD), alem de duas testemunhas (apenas soja ou B. brizantha), no delineamento experimental inteiramente casualizado. A avaliacao nutricional das plantas foi realizada no estadio de pleno florescimento da soja. Na emergencia simultânea das especies, B. brizantha apresentou maior acumulo de N, P, K, S, Mg, Cu, Mn e Fe, enquanto a soja acumulou mais Ca, Zn e B. A soja obteve vantagem no acumulo dos demais nutrientes quando a forrageira emergiu em torno de 7 DD, com maximo acumulo quando B. brizantha emergiu aos 21 DD.

Mobilidade e persistência de herbicidas aplicados em pré-emergência em diferentes solos

The objective of this work was to verify the mobility and persistence of herbicides applied in pre-emergence on different soils and amounts of sugarcane straw. The herbicides ametryn + clomazone (1,500 + 1,000 g i.a. ha-1), isoxaflutole (187,5 g.i.a. ha-1) and diuron + hexazinone (1,170 + 330 g i.a. ha-1) were applied in soil with clayey and medium texture under the following conditions:on 10 and 15 t ha-1 of sugarcane straw followed by rain simulation ; on the ground and covered with 10 t ha-1 of sugarcane straw; on the ground without straw; and control without herbicide. At 10, 20, 40 and 60 days after herbicide application (DAA), species bioindicators such as sorghum and cucumber were sown. Percentage of phytotoxicity was observed at 21 days after emergence. The mixture ametryn + clomazone applied directly on the soil affected the bioindicator up to 40 DAA; however, after this period, the residual effect was smaller. The sugarcane straw affected the performance of this product negatively. The herbicide isoxaflutole applied directly in the soil presented residual effect up to 60 DAA, with 82.5 and 77.5% of bioindicator control, in soils with clayey and medium texture, respectively, and the presence of 10 and 15 t ha-1 of straw did not alter efficiency up to 20 DAA. The herbicide diuron + hexazinone applied on the soil without straw presented residual effect up to 60 DAA, mainly in soil with clayey texture. With 15 t ha-1 of straw, significant reduction was observed in the effectiveness of this mixture.

Lixiviação de clomazone + ametryn, diuron + hexazinone e isoxaflutole em dois tipos de solo

Objetivou-se neste trabalho avaliar a lixiviacao de herbicidas pre-emergentes recomendados para cana-de-acucar em solos com textura argilosa e media. Os ensaios consistiram na aplicacao de ametryn + clomazone (1.500 + 1.000 g ha-1), isoxaflutole (187,5 g ha-1) e diuron + hexazinone (1.170 + 330 g ha-1) no topo das colunas de solo montadas em tubos de PVC. Foram simuladas precipitacoes pluviais de 10, 20, 40 e 80 mm decorridas 24 h da aplicacao dos herbicidas. Os tubos foram desmontados para a semeadura de Sorghum bicolor e de Cucumis sativus, tres dias apos a simulacao. O herbicida ametryn + clomazone em solo com textura argilosa foi detectado aos 20 e 35 cm de profundidade, nas aplicacoes de 10 e 80 mm de agua, respectivamente. Em solo com textura media, observou-se maior efeito deste herbicida em todas as precipitacoes, em relacao ao argiloso. Com a aplicacao de 40 e 80 mm de agua, o herbicida foi detectado ate 35 cm de profundidade em solo com textura argilosa. O herbicida isoxaflutole aplicado em solo argiloso causou albinismo na parte aerea das plantas ate 15 e 25 cm de profundidade no solo com chuvas de 10 e 80 mm, respectivamente. Em solo com textura media, as maiores simulacoes de chuva possibilitaram detectar este herbicida ate 30 cm. Com a simulacao de 80 mm de chuva, o herbicida diuron + hexazinone foi encontrado aos 30 cm de profundidade em ambos os solos, provocando efeitos toxicos sobre as plantas bioindicadoras de 25 e 60% em solos argiloso e medio, respectivamente. Concluiu-se que todos os herbicidas avaliados tem tendencia a serem lixiviados por influencia das precipitacoes pluviais ou de irrigacoes artificiais, com efeitos mais pronunciados em solos com textura media e com menor teor de materia orgânica.

Interação competitiva de Brachiaria brizantha e B. plantaginea sob doses reduzidas de fluazifop-p-butil, aplicadas em diferentes épocas

The objective of this work was to evaluate the competitive interaction between Brachiaria brizantha and B. plantaginea under reduced rates of fluazifop-p-butyl and different application timings. The experimental design was a randomized complete block, with four replications, arranged in a 6 x 3 factorial, consisting of six doses of fluazifop-p-butyl (7,5; 12,5; 18,75; 31,25; 43,75 and 62,5 g ha-1), applied in three times (14, 24 and 34 days after plant emergence - DAE) and a control without herbicide. The highest dose applied corresponded to 33% of the recommended dose for soybean (187,5 g ha-1). The evaluation of the treatments was accomplished 53 DAE. The plants were grouped into leaves and stems, and their dry biomass obtained. Leaf area, stem number and stem length of both species were determined. B. plantaginea was more susceptible to fluazifop-p-butyl than B. brizantha. It was observed that 25 g ha-1 of fluazifop-p-butyl, applied at 14 DAE allowed maximum B. brizantha dry biomass accumulation and satisfactory control of B. plantaginea. In this application timing the dose of 62.5 g ha-1 controlled both species. Regarding application timing, when treated with reduced doses not intended to achieve full species control, young plants of B. brizantha and B. Plantaginea presented better recovery ability.