O objetivo do trabalho foi avaliar os atributos nutricionais e de crescimento do capim-Marandu (Brachiaria brizantha cv. Marandu) submetido a doses de nitrogênio e idades de crescimento. Entre os nutrientes, o nitrogênio destaca-se pelo incremento que é capaz de proporcionar na produção de forragem. O estudo da dinâmica do crescimento e nutrição do capim-Marandu constitui ferramenta importante para o aumento da produção e qualidade dessa planta forrageira. O experimento foi conduzido em casa-de-vegetação, em solução nutritiva, utilizando sílica como substrato. O delineamento experimental utilizado foi o de blocos completos ao acaso, com os tratamentos combinados em fatorial 5x6, com quatro repetições. O capim-Marandu foi submetido a doses de nitrogênio de 28, 112, 210, 294 e 378 mg L-1 e avaliado nas idades de crescimento de 21, 28, 35, 42, 49 e 56 dias após a emergência. As soluções apresentaram proporção constante NO3-:NH4+ de 70%:30% e foram trocadas semanalmente a partir da primeira idade de crescimento. As doses de nitrogênio e as idades de crescimento interagiram significativamente (P<0,05) em todos os atributos nutricionais e de crescimento do capim-Marandu, com exceção do comprimento radicular específico e da taxa de assimilação líquida. As doses de nitrogênio em cada idade de crescimento apresentaram efeito significativo (P<0,05) na produção de massa seca total, massa seca radicular, número de perfilhos, área foliar, comprimento radicular, superfície radicular, concentração de nitrogênio, valor SPAD, razão de área foliar e taxa de crescimento relativo do capim-Marandu. As doses de nitrogênio necessárias para a obtenção da máxima produção de massa seca variaram entre 257 e 304 mg L-1 em função das idades de crescimento. A concentração crítica de nitrogênio determinada nas lâminas de folhas recém-expandidas foi influenciada significativamente (P<0,01) pelas idades de crescimento e variou entre os valores de 33,8 e 12,8 g kg-1 . Os valores SPAD correspondentes às concentrações críticas de nitrogênio foram de 45,0; 45,7; 49,5; 50,2; 45,7 e 35,3 aos 21, 28, 35, 42, 49 e 56 dias, respectivamente. / The objective of this research was to examine nutritional and growth attributes of Marandu grass (Brachiaria brizantha cv. Marandu) under nitrogen rates and growth ages. Among the nutrients, nitrogen stand out by its effects in promoting forage yield. The study of growth dynamic and nutrition of Marandu grass is a important tool to promote the production and quality of this forage plant. The experiment was carried out in glasshouse conditions, with nutrient solution using ground quartz as substrate. The experimental design used was a complete randomized block design, with treatments arranged in a 5x6 factorial, with four replications. The Marandu-grass was grown in nitrogen rates of 28, 112, 210, 294 and 378 mg L-1 and it was evaluated at the ages of 21, 28, 35, 42, 49 and 56 days after seedling emergence. The nutrient solution was prepared with a constant NO3-:NH4+ proportion of 70%:30% and was replaced once a week after the first growth age. Nitrogen rates and growth ages interaction was significant (P<0.05) for all nutritional and growth attributes of Marandu-grass, with exception for the mean net assimilation rate and specific root length. The nitrogen rates in each growth age showed significant effects (P<0.05) on the total dry matter yield, roots dry mass, number of tillers, leaf area, root length, root surface area, nitrogen concentration, SPAD value, leaf area ratio and relative growth rate of Marandu grass. Maximum dry matter production was estimated to occur at nitrogen rates between 257 and 304 mg L-1, depending on plant age. The critical nitrogen concentration determined in the most recently expanded leaf lamina was significantly (P<0.01) influenced by plant ages and ranged from 33.8 to 12.8 g kg-1. SPAD values at the critical nitrogen concentration rates were 45.0; 45.7; 49.5; 50.2; 45.7 and 35.3 for growth periods of 21, 28, 35, 42, 49 and 56 days, respectively.

O objetivo do trabalho foi avaliar os atributos nutricionais e de crescimento do capim-Marandu (Brachiaria brizantha cv. Marandu) submetido a doses de nitrogênio e idades de crescimento. Entre os nutrientes, o nitrogênio destaca-se pelo incremento que é capaz de proporcionar na produção de forragem. O estudo da dinâmica do crescimento e nutrição do capim-Marandu constitui ferramenta importante para o aumento da produção e qualidade dessa planta forrageira. O experimento foi conduzido em casa-de-vegetação, em solução nutritiva, utilizando sílica como substrato. O delineamento experimental utilizado foi o de blocos completos ao acaso, com os tratamentos combinados em fatorial 5x6, com quatro repetições. O capim-Marandu foi submetido a doses de nitrogênio de 28, 112, 210, 294 e 378 mg L-1 e avaliado nas idades de crescimento de 21, 28, 35, 42, 49 e 56 dias após a emergência. As soluções apresentaram proporção constante NO3-:NH4+ de 70%:30% e foram trocadas semanalmente a partir da primeira idade de crescimento. As doses de nitrogênio e as idades de crescimento interagiram significativamente (P<0,05) em todos os atributos nutricionais e de crescimento do capim-Marandu, com exceção do comprimento radicular específico e da taxa de assimilação líquida. As doses de nitrogênio em cada idade de crescimento apresentaram efeito significativo (P<0,05) na produção de massa seca total, massa seca radicular, número de perfilhos, área foliar, comprimento radicular, superfície radicular, concentração de nitrogênio, valor SPAD, razão de área foliar e taxa de crescimento relativo do capim-Marandu. As doses de nitrogênio necessárias para a obtenção da máxima produção de massa seca variaram entre 257 e 304 mg L-1 em função das idades de crescimento. A concentração crítica de nitrogênio determinada nas lâminas de folhas recém-expandidas foi influenciada significativamente (P<0,01) pelas idades de crescimento e variou entre os valores de 33,8 e 12,8 g kg-1 . Os valores SPAD correspondentes às concentrações críticas de nitrogênio foram de 45,0; 45,7; 49,5; 50,2; 45,7 e 35,3 aos 21, 28, 35, 42, 49 e 56 dias, respectivamente. / The objective of this research was to examine nutritional and growth attributes of Marandu grass (Brachiaria brizantha cv. Marandu) under nitrogen rates and growth ages. Among the nutrients, nitrogen stand out by its effects in promoting forage yield. The study of growth dynamic and nutrition of Marandu grass is a important tool to promote the production and quality of this forage plant. The experiment was carried out in glasshouse conditions, with nutrient solution using ground quartz as substrate. The experimental design used was a complete randomized block design, with treatments arranged in a 5x6 factorial, with four replications. The Marandu-grass was grown in nitrogen rates of 28, 112, 210, 294 and 378 mg L-1 and it was evaluated at the ages of 21, 28, 35, 42, 49 and 56 days after seedling emergence. The nutrient solution was prepared with a constant NO3-:NH4+ proportion of 70%:30% and was replaced once a week after the first growth age. Nitrogen rates and growth ages interaction was significant (P<0.05) for all nutritional and growth attributes of Marandu-grass, with exception for the mean net assimilation rate and specific root length. The nitrogen rates in each growth age showed significant effects (P<0.05) on the total dry matter yield, roots dry mass, number of tillers, leaf area, root length, root surface area, nitrogen concentration, SPAD value, leaf area ratio and relative growth rate of Marandu grass. Maximum dry matter production was estimated to occur at nitrogen rates between 257 and 304 mg L-1, depending on plant age. The critical nitrogen concentration determined in the most recently expanded leaf lamina was significantly (P<0.01) influenced by plant ages and ranged from 33.8 to 12.8 g kg-1. SPAD values at the critical nitrogen concentration rates were 45.0; 45.7; 49.5; 50.2; 45.7 and 35.3 for growth periods of 21, 28, 35, 42, 49 and 56 days, respectively.

Diss. (sammanfattning). Uppsala : Sveriges lantbruksuniv., 2003. / Härtill 4 uppsatser.

Accroître la compétitivité des cultures vis-à-vis des adventices est un levier essentiel pour concevoir des systèmes de culture moins dépendants des herbicides. Les légumineuses sont des espèces majeures pour diversifier les systèmes mais elles sont réputées peu compétitives vis-à-vis des adventices. Cependant la variabilité entre espèces en particulier pendant la phase précoce a été peu explorée. Ce travail vise à i) étudier, via deux expérimentations en rhizotrons en serre, les traits impliqués dans la croissance et l’acquisition d’azote (N) en début de cycle chez une gamme d’espèces de légumineuse et les conséquences sur la compétition légumineuse-adventice et à ii) quantifier au champ l’intérêt d’associations légumineuse-non légumineuse (colzalégumineuses, maïs-légumineuses pérennes, la légumineuse étant plante de service) sur la croissance et la composition de la flore adventice. Nous montrons qu’il existe une variabilité entre espèces de capture d’N en début de cycle en lien avec les réserves azotées de la semence et l’exploration racinaire. La croissance et l’acquisition d’N de l’adventice sont impactées différemment selon l’espèce de légumineuse pendant la phase précoce. Les essais au champ montrent l’intérêt de combiner des espèces aux traits complémentaires pour l’utilisation des ressources conduisant à un meilleur contrôle des adventices tout en maintenant la productivité de la culture. Cette étude montre aussi que la composition de la flore est modifiée en fonction de la légumineuse insérée dans le système en lien à la fois avec les traits des légumineuses et les traits de réponse des adventices. / Enhancing crop competitiveness against weeds is a relevant way in order to design cropping system less dependent on herbicides. Legumes are key species in diversified cropping systems but they are known to be low competitive against weeds. However, inter-specific variability especially in the early growth had been little studied. Our work aims to i) study, via two greenhouse experiments in rhizotrons, the traits involved in the growth and nitrogen (N) acquisition for a range of legume species and the impacts on weed-legume competition at the beginning of crop cycle and to ii) quantify under field experiments the interest of legume-non legume intercropping (oilseed rapelegumes, maize-perennial legumes, where legume species were grown as service plant) on weed growth and weed species composition. Our results highlighted the inter-specific variability for soil N uptake in the early growth in relation with seed reserves and rooting exploration. Weed growth and N acquisition are influenced differently as a function of legume species in the early growth. Field experiments show the advantage of species combinations with complementary traits for using resources, leading to better weed control while maintaining crop productivity. This study shows also that weed species composition was modified as a function of legume species in relation with both legume traits and weed traits response.