ABSTRACT:Water is the most important resource for agricultural production. The understanding of water competition mechanisms may lead to the development of new control strategies or coexistence with certain weed species, especially in situations where water is scarce. The objective of this work was to evaluate the competition between cowpea and weeds by water under the effect on plant growth. It was carried out experiment in greenhouse in the period from September to November 2015, in a randomized complete block design, with four replications. The treatments were arranged in factorial 5 x 2, with the first factor corresponding to the competition arrangements between the species (V. unguiculata + C. benghalensis; V. unguiculata + W. indica; V. unguiculata, C. benghalensis and W. indica in monoculture), and the second of water regimes (irrigated and water deficit). The water deficit reduces the growth of cowpea plants, C. benghalensis and W. indica. The competition between plants increases the effects of temporary water deficit in the soil. The W. indica leaf is the organ most affected by the water deficit. The weed specie W. indica has greater capacity competition for water with V. unguiculata than C. benghalensis. Key words: Commelina benghalensis; interference; Vigna unguiculata; Waltheria indica; water stressCompetição entre feijão-caupi e plantas daninhas por água: Efeito no crescimento das plantas RESUMO: A água é o recurso mais importante para a produção agrícola. O entendimento dos mecanismos de competição por água pode propiciar o desenvolvimento de novas estratégias de controle ou convivência com determinadas espécies de plantas daninhas, principalmente nas situações em que a água é escassa. Objetivou-se com este trabalho avaliar a competição entre feijão-caupi e plantas daninhas por água sob o efeito no crescimento das plantas. Foi realizado experimento em casa de vegetação no período de setembro a novembro de 2015, em delineamento em blocos casualizado, com quatro repetições. Os tratamentos foram arranjados em fatorial 5 x 2, com o primeiro fator correspondente aos arranjos de competição entre as espécies (feijão-caupi + trapoeraba; feijão-caupi + malva-branca; feijão-caupi, trapoeraba e malva-branca em monocultivo), e o segundo dos regimes hídricos (irrigado e déficit hídrico). O déficit hídrico reduz o crescimento das plantas de feijão-caupi, Commelina benghalensis e Waltheria indica. A competição entre plantas aumenta os efeitos do déficit hídrico temporário no solo. A folha de W. indica é o órgão mais afetado pelo déficit hídrico. A espécie daninha W. indica tem maior capacidade de competição por água com o feijão-caupi do que a C. benghalensis. Palavras-chave: Commelina benghalensis; interferência; Vigna unguiculata; Waltheria indica; estresse hídricoCompetition between cowpea and weeds for water: Effect on plants growth Rev. Bras.
The capacity of a weed to adapt to the restriction of growth factors is directly related to its ability to compete for those resources with the cultivated species. An experiment was conducted to evaluate the effect of water restriction on the growth and biomass partitioning of four species of weeds. The experimental design used randomized blocks, with five replications. The treatments were arranged in a 4 x 2 factorial, with the first factor being the weed species (Waltheria indica, Crotalaria retusa, Cleome affinis and Commelina benghalensis) and the second, two water regimes: daily irrigation (Irr) and water restriction (WR). The number of leaves, leaf area, dry mass of the plant and its parts (root, stem and leaf), and the mass distribution among different organs (roots, leaves and stems) were determined. The water deficit in the soil increased the root dry matter for C. retusa, W. indica and C. benghalensis, however, it did not alter the mass of the stem of the weeds. C. retusa and W. indica suffered a reduction on the number of leaves, leaf area, dry matter of the leaves and the plant dry matter under water deficit. W. indica and C. retusa had a reduction on the percentage of biomass allocated to the leaves, and an increment on the percentage of the roots mass, while C. benghalensis and C. affinis had an increase only on the roots mass.
The success of the intercropping among cultivated species depends on the adoption of practices that provide, in due course, greater competitive ability of a species over another. The objective of this study was to evaluate the use of glyphosate herbicide in the suppression of Brachiaria (signalgrass) intercropped with maize. The experiment was conducted in a randomized complete block design with four replications. The treatments were arranged in a 5 x 2 + 2 factorial arrangement, the first factor corresponding to the doses of glyphosate (48, 96, 144, 240, 480 g ha-1 of the acid equivalent (a.e)) and the second one to the vegetative stages of the signalgrass at the time of application (2 and 4 tillers). Two controls were added to the treatment list, comprising controls without herbicide application and hand removal of the signalgrass. The number of plants, tillers and dry matter of signalgrass was reduced with glyphosate. The increase of the glyphosate doses enhanced the injure to the forage plants, mainly when the compound was sprayed at the two-tiller vegetative stage. The dry matter of maize plants increased proportionally to the glyphosate dose. However, the height of the maize plants was not affected. The grain mass and productivity of maize grain increased with increasing dose of glyphosate. The maize yield was negatively influenced on the untreated control. Glyphosate at 96 and 144 g ha-1, when applied at 2 and 4 tiller stage, respectively, reduces the growth of signalgrass and does not affect the maize grain yield.
-The commercial mixture of imazethapyr and imazapic herbicides has been used for the control of red rice and several other species of weeds found in rice crops; this system called Clearfield. However, its use may limit the succession of non-tolerant crops for long residual activity. The research objective with this work was to determine the persistence of imazethapyr, imazapic and their mixture in three soils in the Brazilian state of Tocantins. Three experiments were conducted in a completely randomized design with four replications, each corresponding to the evaluated soil (Haplic Plinthosol (FX), red-yellow Latosol (LVA) and Haplic Gleysol (GX)). The treatments were arranged in a split plot design, with the allocated plots herbicides (imazethapyr and imazapic alone and commercial mixture) and the plots allocated the 11 evaluation times (1, 15, 30, 45, 60, 75, 90, 105, 120, 135, 150 days after treatment (DAT)), and a control without application. Contacted up long residual effect of imazethapyr and commercial mixture of imazethapyr and imazapic, regardless of assessed soil. After 150 days of applying herbicides or the commercial mixture, their residues in the soil also inhibited approximately 94% of the mass of the dry matter accumulation of the indicator plants. When imazapic was applied alone, there was a higher dry matter accumulation of the indicator plants, indicating less residual effect of this herbicide in the soil and this was attributed to the lower dose of this herbicide applied. The attributes of the soil pH, texture and iron oxides were what most affected the persistence of the herbicides. It can be concluded that the persistence of imazethapyr and imazapic is too long in the Brazilian state of Tocantins soils and the use of these herbicides in the region should be avoided due to the high risk of the occurrence of carryover,or be well planned, as land use in rotation for susceptible crops. (1, 15, 30, 45, 60, 75, 90, 105, 120, 135 Keywords
-The chemical control of weed is a necessary practice in large-scale agriculture. However, when herbicides are used in the wrong way, they can remain into soil for long periods and/or be leached in its profile, and they may even contaminate groundwater. In this research, clomazone leaching in soil samples collected from different Brazilian regions was estimated by biological method. To do so, columns containing soils were used, and samples were collected every 5 cm. After preparing columns and applying a 1,500 g a.i. ha -1 clomazone dose, rain simulation was performed. Sorghum was used in order to detect the herbicide. More than 60% similarity was found for the studied variables; it was chosen to use only data referring to toxicity percentage. Clomazone did not cause reduction in sorghum cultivated in Organosol, thus indicating a strong herbicide sorption in this soil. Increased pH in Oxisol reduced leaching. More rainfall caused increased herbicide leaching in Oxisol (pH 5.1) and Quartzarenic Neosol. The highest leaching occurred in soils with lower pH and lower organic matter content. It is possible to conclude that, in soils with higher organic matter content, clomazone has lower risks of being leached.Keywords: herbicide, mobility in soil, environmental impact. RESUMO -O controle químico das plantas daninhas é prática consolidada na
-The objective of this work was to evaluate the initial growth and the physiological characteristics of eucalypt submitted to different managements of signalgrass. The experiment was conducted in a protected environment, using a randomized blocks design with five repetitions. The treatments were arranged in a (5 x 2) + 1 factorial design, and the first factor corresponded to the types of weed management (no control; chemical control keeping the signalgrass shoot on the soil; chemical control with removal of the signalgrass shoot; mechanical control keeping the signalgrass shoot on the soil, and mechanical control with removal of the signalgrass shoot); the second factor corresponded to the two weeds species (U. brizantha and U. decumbens) and a control relative to the eucalypt in monoculture. The eucalypt growth was not affected by the presence of the Urochloa species until 50 days after treatments (DAT). However, the coexistence of these species with eucalypt for 107 DAT reduced the collar diameter, total dry matter, and the leaf area, but did not alter the characteristics related to photosynthesis and transpiration. The control method adopted, with removal or maintenance of the signalgrass shoot, regardless of species, did not change the initial eucalypt growth. It can be concluded that the coexistence of eucalypt with Urochloa decumbens or Urochloa brizantha for 105 days reduces the eucalypt growth. However, the use of chemical or mechanical control, with or without removal of signalgrass residue, were effective methods to prevent interference of these weeds.Keywords: control methods, physiological variables, initial growth, Urochloa (syn. Brachiaria), eucalypt. RESUMO -O objetivo deste trabalho foi avaliar o crescimento inicial e as características fisiológicas do eucalipto submetido a diferentes manejos do capim-braquiária. O experimento foi realizado em ambiente protegido, no delineamento de blocos casualizados com cinco repetições. Os tratamentos foram arranjados em esquema fatorial (5 x 2) + 1, sendo o primeiro fator correspondente aos tipos de manejo da planta daninha (ausência de controle, controle químico mantendo no solo a parte aérea do capim-braquiária, controle químico retirando a parte aérea do capim-braquiária, controle mecânico mantendo no solo a parte aérea do capim-braquiária e controle mecânico retirando a parte aérea do capim-braquiária) o segundo às espécies de capim-braquiária (Urochloa brizantha e Urochloa decumbens), além de uma testemunha referente ao eucalipto em monocultivo. O crescimento do eucalipto não foi alterado pela presença das espécies de capim-braquiária até os 50 dias após a aplicação dos tratamentos (DAT
-The initial slow growth and short stature of carrot can allow that weeds settle in crop areas, requiring the management of these plants for productivity not to decrease. Nevertheless, weeds control has been difficult because there are few herbicides available for weeds control in postemergence of carrots. Two experiments in the field were carried out to evaluate selectivity of metribuzin applied in postemergence of carrots. A experimental randomized block design was utilized with four repetitions. Treatments consisted of metribuzin doses (0, 144, 288, 432, 576, 720, 960 and 1,200 g ha -1 ), applied in postemergence of carrots of the Nantes variety. Roots productivity was evaluated and percentage of commercial roots and no-commercial roots was calculated. Metribuzin has not caused visual symptoms of intoxication in carrots. Doses lower than 432 g ha -1 of metribuzin do not reduce the total productivity of roots, independent of the application period. Any doses of metribuzin changed the percentage of commercial and noncommercial roots. It is concluded that metribuzin is selective for carrots of the Nantes variety in postemergence applications at doses of 432 g ha -1 .
-Knowledge of herbicides sorption by colloids predicts its movement in the soil profile and its effectiveness in controlling weeds and crops poisoning when directly applied to the soil. This knowledge becomes even more important for herbicides which have long persistence in the soil. In this research, clomazone sorption was estimated by the biological method in Brazilian soil samples with different physical and chemical characteristics, cultivated with sugarcane crops. As an indicator of the presence of clomazone in the soil, Sorghum bicolor was used. The data relating to assessments of poisoning and accumulation of dry matter of the plants were subjected to multivariate analysis of similarity among variables. After that, clomazone doses that caused 50% of intoxication in sorghum plants grown (C 50 ) as well as sorption ratio (SR) of the herbicide in different soil types were estimated. There was similarity greater than 80% for data regarding the percentage of intoxication and accumulated dry matter, with the option to use only those related to the first variable. RS and C 50 were higher in Organosol and lower in red-yellow Latosol with and without changing the pH. It was concluded that the clomazone dose to be recommended must be differentiated for different soils, since the value of clomazone sorption in the soil is dependent on its attributes, and the organic matter content is of the utmost importance.Keywords: herbicide retention, herbicide behavior in the soil, pollution potential, herbicides impact. RESUMO -O conhecimento
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