A análise da fluorescência da clorofila a vem sendo utilizada para melhorar o entendimento dos mecanismos da fotossíntese, bem como, na avaliação da capacidade fotossintética das plantas alterada por estresses bióticos ou abióticos. Objetivou-se com esse trabalho avaliar a sensibilidade de plantas de mandioca à herbicidas com diferentes mecanismos de ação, bem como, os danos causados pela aplicação desses herbicidas no aparato fotossintético destas plantas. Para isso foi realizado um experimento no delineamento em blocos casualizados, com quatro repetições. Os tratamentos foram constituídos da aplicação em pós-emergência da mandioca dos seguintes herbicidas: bentazon, clomazone, fomesafen, fluazifop-p-buthyl, glyphosate, nicosulfuron, chlorimuron, fluazifop-p-buthyl + fomesafen, sulfentrazone, além de uma testemunha sem aplicação. As avaliações de intoxicação visual e fluorescência da clorofila a foram realizadas aos 2, 9, 16 e 23 dias após a aplicação dos herbicidas. Os herbicidas avaliados afetaram de forma diferenciada as plantas de mandioca, sendo que, o glyphosate e sulfentrazone promoveram a morte das plantas. Os herbicidas clomazone, fomesafen, fluazifop-pbuthyl e chlorimuron-ehtyl causaram baixa intoxicação as plantas de mandioca e não afetaram a relação Fv/Fm e a ETR. No entanto, para o nicosulfuron e a mistura fluazifop-p-buthyl + fomesafen os valores da Fv/Fm estiveram abaixo do ideal nas primeiras épocas de avaliação mas as plantas tratadas com esses herbicidas se recuperam. As variáveis fisiológicas avaliadas podem ser utilizadas como forma de avaliar a seletividade de herbicidas a mandioca, pois apresentaram respostas semelhantes aos observados para a intoxicação visual da cultura. Palavras-chave: Manihot esculenta Crantz, fotossíntese, taxa de transporte de elétrons, fluorescência da clorofila a AbstractAnalysis of chlorophyll a fluorescence has been used to improve the understanding of the mechanisms of photosynthesis, as well as in the evaluation of plant photosynthetic capacity altered by biotic or abiotic stresses. The objective of this study was to evaluate the sensitivity of cassava plants to herbicides with different mechanisms of action, as well as the damage caused by the application of herbicides on the photosynthetic apparatus of these plants. An experiment was conducted in a randomized block design with four replications. The treatments were constituted of the application of the following post-1 Dr. em Fitotecnia, Engº Agrº, UFVJM, Universidade Federal dos Vales do Jequitinhonha e Mucuri, Diamantina, MG.

Fitomassa de adubos verdes e cobertura do solo na região do Alto Vale do Jequitinhonha, Minas Gerais Palavras-chave -Cajanus cajan. Canavalia ensiformis. Crotalaria spectabilis. Lablab purpureus. Mucuna deenringianaAbstract -Green manuring is a positive practice that reduces the impact on agricultural production systems aimed at sustainable land use. The objective of this study was to evaluate the performance of six legumes used for green manure, the productivity of biomass, land cover and use of photosynthetic active radiation in the region of the Vale do Jequitinhonha, Minas Gerais, Brazil. The experiment was conducted during March to October, 2010 in randomized block design with four replications. Green manures were used: Crotalaria spectabilis, Canavalia ensiformis, Cajanus cajan, Lablab purpureus, Mucuna deenringiana and Lupinus albus. Green manures had high yields of biomass, however, different peaks of ground cover and radiation interception were observed. The largest accumulations of dry and fresh matter were observed in C. spectabilis followed by C. cajan. Among the species studied, C. ensiformis has a larger growing season, representing great potential for soil covering, and is important for the interception of photosynthetically active radiation.

Crop-weed competition is extensively studied in weed science. The additive design, in which weed density varies and the crop density is kept constant, is the most commonly utilised design in plant competition studies. The additive design is important to calculate economic weed thresholds and improve weed control decision-making. Crop-weed competition studies are usually conducted by weed scientists, who sometimes report misleading conclusions because of lack of statistical knowledge needed for data analysis of such studies. Therefore, the objective of this manuscript is to provide the concept of additive design and demonstrate the model selection approach for describing crop-weed density relationship to non-statisticians. We evaluated three models routinely used in the literature to interpret data from additive designs, including polynomial quadratic, sigmoid and rectangular hyperbola curves. Based on the described statistical criteria, we demonstrated the rectangular hyperbola to be the most appropriate model to describe data from an additive design study looking at Richardia brasiliensis and Commelina benghalensis competition with maize (Zea mays). Moreover, we describe step-by-step how to perform the statistical analysis in R software and interpret the results of crop-weed competition studies. We suggest the use of the rectangular hyperbola as a standardised model for crop-weed competition in additive design.

RESUMO Nos cultivos consorciados, a competição entre as espécies pelos recursos do meio pode inviabilizar o sistema. A intensidade da interferência de uma espécie sobre a outra

Growth of cassava and weed in response to phosphate fertilizerFertilizers may be used to change the competitive relations, favoring the crop species, providing the competing species have different responses to the nutrient application. Thus, the aim of this study was to evaluate the growth of Cassava plant, Bidens pilosa L. and Brachiaria decumbens Stapf, as a function of the amount of P supplied at planting. The experiment was conducted in a greenhouse and the, treatments were arranged in a 3 x 4 factorial, involving the three species studied and four levels of phosphate fertilization (absence of P 2 O 5 , 80 kg ha -1 , 800 kg ha -1 and 4000 kg ha -1 P 2 O 5 , equivalent to 0, 1, 10 and 50 times the phosphorus dose recommended, respectively). A randomized block design was used, with five replications. The application of phosphate fertilizer promoted larger growth of the species evaluated, and cassava had higher growth of the shoot with the increased availability of phosphorus. In general, weeds showed higher responses to lower doses of phosphorus.

-The chemical composition and the accumulation of nutrients in stems, leaves and fruits are essential information to meet the nutritional requirements of a peanut crop. Thus, the goals of the present study were to evaluate the rate of absorption of macro-and micronutrients; identify the critical phases of nutrient absorption in the peanut crop; and perform growth analysis of these plants. For this, an experiment under field conditions using randomized blocks with 15 treatments and four repetitions was assembled. Each treatment corresponded to a sampling time, held from 10 days after planting, until the end of the cycle, which corresponded to 160 days. Peanut plants generally showed higher macro-and micronutrient absorption rates at 110 days after emergence, coinciding with the highest growth rate of the crop. Thus, the higher nutrient absorption rate and increased crop growth rate occurred during the reproductive period, formation of fruit and grain filling.Keywords: Arachis hypogaea L.. Growth rate. Plant nutrition. ABSORÇÃO DE NUTRIENTES E CRESCIMENTO DE PLANTAS DE AMENDOIMRESUMO -A composição química tanto quanto o acúmulo de nutrientes em caule, folhas e frutos são informações imprescindíveis para conhecer as exigências nutricionais da cultura do amendoim. Dessa forma, objetivou-se com o presente estudo avaliar a taxa de absorção de macro e micronutrientes, além de identificar as fases críticas de absorção de nutrientes na cultura do amendoim, bem como, realizar a análise de crescimento dessas plantas. Para isso foi montado um experimento em condição de campo no delineamento experimental em blocos ao acaso, com 15 tratamentos e 4 repetições. Cada tratamento correspondeu a uma época de amostragem, realizadas de 10 em 10 dias após o plantio da espécie, até o final do ciclo da cultura, que correspondeu há 160 dias. Foi observado de modo geral nas plantas de amendoim maior taxa de absorção de macro e micronutrientes aos 110 dias após a emergência, período que coincidiu com a maior taxa de crescimento da cultura. Assim, a maior taxa de absorção de nutrientes e a maior taxa de crescimento da cultura ocorreram durante o período reprodutivo, formação dos frutos e enchimento dos grãos. Palavras-chave:Arachis hypogaea L.. Nutrição de plantas. Taxa de crescimento.

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-Glyphosate is a non-selective herbicide used for weed control in eucalyptus forests. Glyphosate drifts are common and may cause serious damage to crops. An alternative to reduce such effects is to use antidotes capable of protecting eucalyptus. An experiment was conducted to evaluate the effects of the application of liquid fertilizer on eucalyptus plants subjected to a glyphosate drift simulation. The treatments were arranged in a 5 x 5 factorial design. The first corresponding factor was liquid fertilizer (0, 1, 2, 4, and 8 L c.p. ha -1 of Fertiactyl Pós ® ) and the second factor dose of glyphosate drift (0, 360, 720, 1,440, and 2,160 g e.a. ha -1 ). The products were applied together so that the spray did not reach the upper third of the plants. At 7, 28, and 49 days after application (DAA), the percentage of intoxication of eucalyptus was evaluated. At 56 days DAA, height, leaf area, leaf nutrient contents, and shoot and root dry matter were determined. Higher doses of glyphosate (1,440 and 2,160 g ha -1 ) caused intoxication levels above 90% at 28 and 49 DAA without using liquid fertilizer. The combination of 2,160 g ha -1 of glyphosate with 8.0 L ha -1 of liquid fertilizer resulted in an estimated eucalyptus dry matter 7% higher than in the control and 97% higher than using 2,160 g ha -1 of glyphosate without the liquid fertilizer. We conclude that the liquid fertilizer was effective in suppressing the harmful effects caused by glyphosate on eucalyptus plants. Keywords