-Two experiments were carried out to evaluate the initial plant growth of Eucalyptus urograndis growing in coexistence with Urochloa decumbens and U. ruziziensis. In 100-L box, one plant of U. decumbens or U. ruziziensis grew in coexistence with one plant of E. urograndis clones C219H or H15, respectively, in the distances of 0, 5, 10, 15, 20, 25, 30, 35, and 40 cm from the crop. After 30, 60, 90 (both clones), and 150 days (just for H15), growth characteristics were evaluated. Plants of both clones, growing in weed-free situations, showed a better growth and development than plants that grew in weedy situations, independently of the distance, having the highest plant height, stem diameter, dry mass of stem, and dry mass of leaves. As the same way, the number of branches, number of leaves, and leaf area of the clone C219H were similarly affected. Urochloa ruziziensis reduced the dry mass accumulation of stem and leaves by the rate of 0.06 and 0.32 g per plant, respectively, per each centimeter growing nearest to the crop, while U. decumbens reduced by 0.03 and 0.14 g per plant. The interference of U. decumbens and U. ruziziensis with E. urograndis is more intense when weedy plants grow in short distances from the crop. 0, 5, 10, 15, 20, 25, 30, 35 Keywords: Eucalyptus urograndis, Urochloa decumbens, Urochloa ruziziensis, weed competition. RESUMO -Dois experimentos foram realizados para avaliar o crescimento inicial das plantas de Eucalyptus urograndis crescendo em convivência com Urochloa decumbens e U. ruziziensis. Em vasos de concreto de 100 L, uma planta de U. decumbens ou U. ruziziensis cresceu em coexistência com uma planta de E. urograndis, dos clones C219H ou H15, respectivamente, nas distâncias de

RESUMO - O trabalho teve como objetivo determinar o efeito da adubação nitrogenada de cobertura sobre a comunidade infestante e sobre os períodos de interferência das plantas daninhas na cultura do sorgo granífero ‘882’, em sistema convencional. Foram estudados os períodos de convivência e controle de 0, 7, 14, 32, 42, 57, 72 e 118 dias após a emergência (DAE), totalizando dezesseis tratamentos, dispostos em blocos casualizados, com quatro repetições, em dois níveis de adubação, 0 e 70 kg ha-1 de N. A adubação não alterou a composição da comunidade infestante, destacando-se Raphanus raphanistrum, Cyperus rotundus, Alternanthera tenella e Amaranthus ssp. como as espécies de maior importância relativa. Os períodos críticos de prevenção da interferência (PCPI) do sorgo ‘822’ com e sem adubação foi de 4 aos 72 e 7 aos 90 DAE, respectivamente. A interferência das plantas daninhas reduziu em 31 e 26% a produtividade estimada de 6859,5 e 6417,1 kg ha-1 de grãos do sorgo na presença e na ausência da adubação nitrogenada, respectivamente, sendo que adubação nitrogenada realizada aos 45 dias após a emergência da cultura aumentou em 7% a sua produtividade.Palavras-chave: Sorghum bicolor, competição, nitrogênio. WEED INTERFERENCE PERIODS ON GRAIN SORGHUM CROP WITH AND WITHOUT NITROGEN FERTILIZATION  ABSTRACT - The aim of this work was to determine the effect of nitrogen fertilization on the weed community and on the periods of interference of weeds in the ‘882’ grain sorghum in a conventional system. The periods of coexistence and control were 0, 7, 14, 32, 42, 57, 72 and 118 days after emergence (DAE), totaling sixteen treatments, arranged in randomized blocks, with four replications, at two levels of fertilization, 0 and 70 kg ha-1 of N. Fertilization did not change the composition of the weed community, with the species Raphanus raphanistrum, Cyperus rotundus, Alternanthera tenella and Amaranthus ssp. being the most important at all levels of fertilization. The critical periods of interference prevention (CPIP) of sorghum ‘822’ with and without fertilization were 4 at 72 and 7 at 90 DAE, respectively. Weed interference reduced the estimated yield of 6859.5 and 6417.1 kg ha-1 of sorghum grains by 31 and 26% in the presence and absence of nitrogen fertilization, respectively, and nitrogen fertilization done at 45 days after the emergence of the crop increased its productivity by 7%.Keywords: Sorghum bicolor, competition, nitrogen.