Renan Rodrigues Braga

Determinação de espécies bioindicadoras de resíduos de herbicidas auxínicos

Herbicides that present soil residual activity may become a problem in agricultural crops due to the possibility ofcrops successors intoxication. It is hard to detect residues of hormonal herbicides using the bioassay technique, dueto the variation in the growth response of the indicator plant. The objective of this work was to select plants andvariables susceptible to the herbicides 2,4-D and picloram for soil residue indication..T o make it possible, two bioassayswere performed,, where each of them consisted of 60 treatments in a factorial scheme with the combination of threeplant species (Lycopersicon esculentum, Cucumis sativus and Beta vulgaris), two substrates (sand and soil sample)and 10 subdoses of herbicide (0, 3, 6, 12, 22.5, 47, 94, 187.5, 375 and 750 g ha

ALOCAÇÃO DE MATÉRIA SECA E CAPACIDADE COMPETITIVA DE CULTIVARES DE MILHO COM PLANTAS DANINHAS 1

The competitive ability of crops against weeds depends on factors related to their ability to maintain productivity or eliminate them in a situation of interference. This study aimed to evaluate the effects of competition between three varieties of maize and six weed species on the growth and dry mass allocation by plants. A factorial scheme 3 x 6 + 9 was arranged consisting of a combination of three genotypes of maize (DKB 390 YG, variety and hybrid AL 25 SHS 4080) in competition with six weed species (Bidens pilosa, Cenchrus echinatus, Brachiaria brizantha, Commelina benghalensis, Brachiaria plantaginea and Euphorbia heterophylla), plus nine treatments corresponding to the maize and weed cultivars under no competition. Both treatments were designed in randomized blocks with four replicates and each pot (containing 5 dm3) was an experimental unit. The period of coexistence among the maize and weed cultivars was 60 days after emergence, and thereafter the plant material collected was evaluated to assess the dry mass distribution among different organs (roots, leaves and stems). The maize cultivars presented lower dry mass accumulation when in competition with the weed species. The leaves and stems were the main organs negatively affected. On the other hand, the roots of the competing species were, in general, the most affected. AL 25 genotype was the least tolerant maize variety in competition with weeds and B. plantaginea was the least competitive weed. B. brizantha and C. benghalensis proved to be the species with the greatest capacity to compete with maize.

Eficiência nutricional de cultivares de feijão em competição com plantas daninhas

Apesar do ciclo efetivamente rapido do feijoeiro, a habilidade no uso dos nutrientes adicionados por ocasiao do plantio e cobertura pode ser prejudicada pela presenca de determinadas especies de plantas daninhas. Objetivou-se com este trabalho avaliar os efeitos da competicao entre tres cultivares de feijao (IPR Colibri, IPR Eldorado e Perola) e seis especies de plantas daninhas (Euphorbia heterophylla, Bidens pilosa, Cenchrus echinatus, Amaranthus spinosus, Commelina benghalensis e Brachiaria plantaginea) no acumulo de N, P e K pelas plantas e na eficiencia nutricional do feijoeiro. O experimento foi realizado em condicoes controladas de temperatura e umidade, em delineamento de blocos casualizados, com quatro repeticoes. O periodo de convivencia entre os cultivares de feijao e as plantas daninhas foi de 45 dias apos emergencia da cultura. Os cultivares de feijao apresentaram reduzido acumulo relativo de N, P e K quando estavam em competicao, sendo o sistema radicular o principal orgao afetado negativamente. O cultivar IPR Colibri foi o que menos tolerou a competicao com plantas daninhas e E. heterophylla foi a especie com menor poder de competicao, enquanto A. spinosus e B. plantaginea foram as mais competitivas com a cultura do feijao. A eficiencia nutricional do feijoeiro variou conforme o genotipo de feijao e a especie infestante.

Ocorrência de plantas daninhas no sistema lavoura-pecuária em função de sistemas de cultivo e corretivo de acidez

Os estudos das interacoes entre plantas daninhas, culturas e sistemas de plantio podem proporcionar o entendimento de novas formas de implantacao, recuperacao e renovacao das pastagens. Assim, objetivou-se estudar a fitossociologia de plantas daninhas em implantacao de pastagem por meio da integracao lavoura-pecuaria, em cultivo safrinha. Admitindose a necessidade de aplicacao de corretivo, os tratamentos resultaram da combinacao de dois sistema de plantio (semeadura direta e aracao seguida pela gradagem) e quatro doses de corretivo da acidez (0, 1/3, 1/2 e 1 vezes a recomendacao). Observou-se que plantas do genero Sida apresentam maiores indices de valor de importância em todos os tratamentos. As especies Sida urens e Sida rhombifolia foram as mais representativas. Os indices de valor de importância do genero Sida foram crescentes com as doses do corretivo, apresentando valores maximos com metade da dose recomendada de calcario, com posterior decrescimo. Ocorreram, tambem, especies toxicas aos animais de pastejo, alem de gramineas e leguminosas forrageiras, que podem ser beneficas ao sistema. As especies de gramineas perenes apresentaram maiores valores de importância em plantio convencional do que em plantio direto, possibilitando o uso de herbicidas especificos para o primeiro sistema. Comparando o plantio direto com o plantio convencional, o indice de similaridade foi igual a 81,1%, o que e considerado alto. Em geral, o plantio convencional apresentou ainda maior densidade de plantas daninhas que o plantio direto.

Fitossociologia de plantas daninhas em cultivos de feijão sobre diferentes manejos de herbicidas

Knowledge on changes in weeds communities caused by weeds management practices is important when effective strategies for the control of these species are set. A field experiment was conducted to assess the effects of herbicides applications with different sprayer boom heights on the weeds dynamics and beans yield. A 3x4+1 factorial arrangement was adopted, comprised of the combination of three herbicides (fomesafen. fluazifop-p-butyl and a mixture of both) and four different boom heights (0.20; 0.30; 0.40 and 0.50 m above target) and one control (non-weeded check). Thirty days after application (DAA), the following phytosociological indices were determined: relative frequency, relative density, relative dominance, and importance value. Sixty days DAA, yield rates were determined. Prior to the experiment installation, 22 species were identified in the entire experimental area. The species Alternanthera tenella , C helidonium majus , D igitaria horizontalis and Bidens pilosa dominated the area where there was no weed control. Reduced boom heights for application of fomesafen diminished the importance of dicot species. In the plots with fomesafen + fluazifop-p-butyl applications, the number of dicot weeds was greater than the other species, with predominance of A. tenella e B. pilosa . In general, the similarity index between the different herbicides and different boom heights was low, which indicates that the treatments used result in different weeds populations. Bean crops reduces the weeds diversity, and the application of herbicides has a positive effect on weeds infestation, with consequent gains in productivity.

Crescimento inicial da cultura da mandioca em sistema de policultivo

One of the main reasons why farmers in different regions prefer polycultures is that very often you can get higher yields in an area sown in polyculture than in monoculture with an equivalent area. Thus in systems polycultures the plants are in a state of permanent competition causing a reduction in plant growth consorts. The competition affects the production quantitatively and qualitatively, because it changes the efficiency of utilization of environmental resources such as water, light and nutrients, settling between culture and plants of other species existing on site. This competition also occurs between individuals of the same species or between biotypes prevalent in the area. Thus, the aim of this study was to evaluate the growth of two cultivars of cassava intercropped with crops of corn, beans and green manure (gaundu dwarf beans). Treatments consisted of the consortium is cassava ( Manihot esculenta ), IAC-12, with green manure, dwarf pigeonpea ( Cajanus cajan ), maize ( Zea mays ) and beans ( Phaseolus vulgaris ) beyond cropping of cassava with and without weed control. The development of cultivars was negatively influenced by weed infestation. Cultivation in consortium with two cultivars of maize, beans and faba bean dwarf caused no significant effects on cassava as compared to the same crop grown in single system with weeding.