RESUMO Objetivou-se avaliar o efeito do sombreamento arbóreo sobre as características morfogênicas e estruturais dos perfilhos e acúmulo de forragem do capim-Tanganica ( Megathyrsus maximus Jacq. cv. Tanganica). Para tanto, um experimento foi conduzido, de dezembro de 2010 a março de 2012, sob delineamento inteiramente casualizado com quatro tratamentos (níveis de sombreamento) e cinco repetições. Foram avaliados: filocrono (FIL), taxas de alongamento de lâminas foliares (TAlLF) e de colmos (TAlC), número de folhas vivas por perfilho (NFVP), comprimento de lâminas foliares (CLF), comprimento de colmo (CC), densidade populacional de perfilhos (DPP), taxas de crescimento de lâminas foliares (TCLF) e de colmos (TCC), taxa de senescência (TS) e taxa de acúmulo de forragem (TAF). Exceto para TAlLF e NFVP, todas as demais varáveis morfogênicas foram influenciadas (P<0.05), de maneira positiva ou negativa pelos níveis de sombreamento. Exceto na primavera, a DPP aumentou linearmente sob maiores níveis de sombreamento (P<0.05). Em nível de perfilho, exceto na primavera, o CLF aumentou linearmente com o aumento do nível de sombreamento (P<0.05). Além disso, de maneira geral, o CC reduziu de maneira linear com o aumento do nível de sombreamento. Quanto às taxas de crescimento, o verão II e a primavera proporcionaram maiores valores, e as menores taxas foram registradas no outono (P<0.05). Os ajustes das características morfogênicas e estruturais garantiram ao capim-Tanganica ótima adaptação ao ambiente sombreado.

ABSTRACT This study aimed to evaluate the effect of tree shading levels on tillers’ morphogenetic and structural traits, besides the herbage accumulation of Tanganyika grass ( Megathyrsus maximus Jacq. cv. Tanganyika). For that, an experiment was carried out from December 2010 to March 2012, under a completely randomized design, with four treatments (shading levels) and five repetitions. Phyllochron (PHY), leaf and stem elongation rates (LER and SER, respectively), number of leaves per tiller (NLT), leaf blade length (LBL), stem length (ST), tiller population density (TPD), leaf (LGR) and stem growth rates (SGR), senescence rate (SR) and herbage accumulation rate (HAR) were assessed. Excepted by the LER and NLT, the shading levels influenced the other morphogenetic variables (P<0.05), positively or negatively. Except in the spring, the TPD linearly increased because of the shading levels (P<0.05). At tiller level, except in the spring, the LBL linearly increased with the shading levels (P<0.05). In general, the SL linearly decreased with the shading levels. Regarding the growth rates, summer II and spring provided greater values, and the lowest one occurred in autumn (P<0.05). The adjustments of both morphogenetic and structural traits ensured the Tanganyika grass a great adaptation to the shaded environment.

RESUMO A adaptação edafoclimática das variedades e/ou clones de cana-de-açúcar pode garantir maior produtividade de forragem para a alimentação animal. Para tanto, foi elaborado um experimento no campus de Seropédica da Universidade Federal Rural do Rio de Janeiro, para avaliação de duas variedades (RB867515 e RB969017) e dois clones (RB058046 e RB098022) de cana-de-açúcar, sob um delineamento de blocos casualizados, com sete repetições. Foram avaliadas variáveis biométricas, perfilhos m-1, índice de área foliar (IAF), Grau Brix e índice de maturação (IM), além das produtividades de forragem e total durante o cultivo do ciclo de cana-planta. O plantio foi realizado em 08/10/2018 e a colheita em 13/09/2019, aos 323 dias após plantio (DAP). Os dados foram analisados pelo software R, sob blocos ao acaso, e medidas repetidas no tempo para as variáveis biométricas, perfilhos m-1, IAF, Grau Brix e IM. As médias foram comparadas pelo teste Tukey (p < 0,10). O clone RB098022 apresentou 20,2% mais perfilhos m-1 que ambas as variedades. Aos 296 DAP ambos os clones e a variedade RB969017 apresentaram IM maiores que 0,85, caracterizando-os como de ciclo mais precoce do que a variedade RB867515 (IM = 0,91 aos 323 DAP). Maiores produtividades e semelhantes de forragem e total foram verificadas para o clone RB098022 e a variedade RB867515 (médias de 141,6 e 151,2 Mg ha-1, respectivamente). Todos os materiais genéticos se adaptaram às condições edafoclimáticas durante o cultivo decana-planta, sendo recomendado a utilização do clone RB098022 e da variedade RB867515 para a alimentação animal na região da Baixada Fluminense. Todos os materiais genéticos se adaptaram às condições edafoclimáticas durante o cultivo decana-planta, sendo recomendado a utilização do clone RB098022 e da variedade RB867515 para a alimentação animal na região da Baixada Fluminense.

ABSTRACT The edaphoclimatic adaptation of sugarcane varieties and clones can ensure higher forage productivity for animal feed. An experiment was conducted at the Seropédica campus of the Federal Rural University of Rio de Janeiro for the evaluation of two varieties (RB867515 and RB969017) and two clones (RB058046 and RB098022) of sugarcane under a randomized block design with seven replications. Biometric variables, tillers m-1, leaf area index (LAI), Brix degree, maturation index (MI), as well as forage and total yields, were evaluated during the cultivation of the sugarcane-plant cycle. Sugarcanes were planted on 10/08/2018 and harvested on 09/13/2019, totaling 323 days after planting (DAP). The data were analyzed using the R software, under randomized blocks and repeated measurements in time for biometric variables, tillers m-1, LAI, Brix Degree and MI. Means were compared using the Tukey test (p < 0.10). Clone RB098022 presented 20.2% more tillers m-1 than both the other varieties. At 296 DAP, both clones and the variety RB969017 presented MI higher than 0.85, indicating them as an earlier cycle than the variety RB867515 (MI = 0.91 to 323 DAP). Higher and similar forage and total yields were obtained with clone RB098022 and variety RB867515 (means 141.6 and 151.2 Mg ha-1, respectively). All sugarcanes adapted to edaphoclimatic conditions during plant cane cultivation, and it is recommended to use the clone RB098022 and the variety RB867515 for animal feed in the Baixada Fluminense region.

A adubação nitrogenada atua na aceleração do aparecimento e mortalidade de perfilhos, alterando o perfil etário da população. Perfilhos de idades diferentes possuem capacidades distintas de resposta a fatores de meio e de manejo, caracterizadas por variação em suas respostas morfogênicas, o que interfere sobremaneira no acúmulo de forragem. Nesse sentido, as variáveis taxa de aparecimento e alongamento foliar e duração de vida das folhas foram utilizadas como descritores para identificar as classes de idade de perfilhos em pastos de capim-marandu, mantidos a 30cm por meio de lotação contínua e taxa de lotação variável, utilizando-se o procedimento multivariado de análise de agrupamentos (Cluster analysis). Foi utilizado o método da distância média, segundo as médias conjuntas dos caracteres avaliados e, com base nesses resultados, um dendograma foi construído. O agrupamento segundo as características morfogênicas taxa de aparecimento e alongamento foliar e duração de vida das folhas revelou variações significativas entre três faixas etárias: perfilhos jovens (0 a 60 dias), perfilhos maduros (60 a 120 dias) e perfilhos velhos (com mais de 120 dias). A discriminação das faixas etárias de acordo com a dose de nitrogênio seguiu o mesmo padrão de agrupamento, indicando valores de referência para futuros estudos mais detalhados acerca da ecofisiologia do capim-marandu.

Nitrogen fertilization augments tiller appearance and death, modifying the age profile of tiller population. Tillers from different age categories present distinct responses to environmental factors and management practices characterized by variation in their morphogenetic responses, which interfere in the dynamics of the herbage accumulation process. In that context, rates of leaf appearance and elongation and leaf lifespan were used as indicators to identify tiller age categories of continuously stocked marandu palisade grass managed at 30cm and subjected to nitrogen fertilization regimes using cluster analysis. Analysis was based on the average distance method using combined means of the response-variables studied, and the results used to build a dendogram to illustrate the arrangement of the resulting clusters. Three clusters were identified corresponding to the tiller age categories denominated young (tillers with age between 0 and 60 days), mature (between 60 and 120 days) and old (over 120 days). Discrimination of the tiller age categories according to nitrogen fertilization regime followed the same pattern of clustering. The fact demonstrates consistency and indicates the three age categories as reference for detailed studies regarding the ecophysiology of marandu palisade grass.

Nitrogen fertiliser accelerates plant growth and increases herbage utilisation efficiency in continuously stocked temperate grass swards, indicating greater herbage production and harvest efficiency. There is no similar evidence, however, for tropical pastures. In this study we evaluated the morphogenetic responses, the patterns of defoliation and the efficiency of herbage utilisation of continuously stocked marandu palisade grass (Brachiaria brizantha (Hochst. ex A. Rich.) Stapf. cv. Marandu) maintained at 30 cm by cattle and fertilised with nitrogen. Treatments corresponded to four measures of nitrogen application (0, 150, 300 and 450 kg ha–1), and were assigned to experimental units (1,200 m2 paddocks) according to a randomised complete block design, with four replications. There was a seasonal pattern of variation in the morphogenetic responses and in herbage utilisation efficiency (HUE) characterised by higher herbage growth rates and HUE during late spring and summer. Nitrogen fertilisation increased both leaf appearance and elongation rates (around 60 % between non-fertilised and swards fertilised with 450 kg ha–1, p < 0.05), requiring higher stocking rates (average of 1.6, 2.6, 2.9 and 3.1 Animal Unit (adult animal weighing 450 kg) ha–1 for 0, 150, 300 and 450 kg ha–1, respectively) to maintain the management target. Although the frequency of leaf defoliation increased (with no change in defoliation severity - 56.1 ± 1.88 %), the leaf lifespan decreased, resulting in a similar number of defoliations during the leaf lifespan (average of 0.91 ± 0.069). This resulted in increased HUE only for the 150 kg ha–1 treatment relative to non-fertilisation (37.5, 48.1, 44.0 and 44.5 ± 2.25 % for 0, 150, 300 and 450 kg ha–1 N, respectively), indicating that with nitrogen fertilisation rates above 150 kg ha–1, there are compensatory mechanisms related to morphogenetic responses that buffer changes in utilisation efficiency.

The objective of this experiment was to evaluate the structural characteristics of young, mature and old tillers on continuously stocked marandu palisade grass maintained at 30 cm and fertilized with nitrogen. Treatments corresponded to three nitrogen application rates (150, 300 and 450 kg/ha of N) plus control (no fertilization) and were assigned to experimental units (1,200-m² paddocks) according to a completely randomized block design, with four replications. Measurements were performed during fall/winter 2007 and summer 2008. During summer, young tillers showed longer leaves and shorter stems relative to old tillers. During fall/winter, young and old tillers showed shorter leaves, while mature and old tillers showed longer stems. Tiller age interfered with the number of leaves per tiller mainly through variations in the number of expanding and senescing leaves during both fall/winter and summer. The structural characteristics of individual tillers are affected by plant age, with nitrogen favouring the production of leaf tissue in young tillers during summer.

Knowledge regarding morphogenetic characteristics has contributed to the understanding of plant responses to variations in climatic conditions and management practices. However, the original framework has been developed for temperate grass species, and indicates no ontogenetic effect on the expression of morphogenetic traits. Similar information for tropical grass species is scarce, but not less important. This experiment aimed at evaluating the influence of tiller age on the morphogenetic characteristics of continuously stocked marandu palisadegrass swards maintained at 30 cm and fertilized with nitrogen (N). Treatments corresponded to three nitrogen application rates (150, 300 and 450 kg ha-¹ of N) plus the control (no fertilization) and were assigned to experimental units (1,200 m² paddocks) according to a complete randomized block design, with four replications. The following response variables were measured during autumn/winter (Jun. to Jul. 2007) and summer (Feb. to Mar. 2008): leaf appearance rate (LAR), leaf elongation rate (LER) and the age profile of the tiller population. In general, LAR and LER were higher on young (< 2 months old) relative to mature (2 to 4 months old) and old (> 4 months old) tillers during both autumn/winter and summer. During autumn/winter swards were mainly comprised of old tillers (> 4 months old), the opposite happening during summer, when they were mainly comprised of young tillers. Overall, there was no N effect within tiller age categories. Tiller age was an important factor interfering with the morphogenetic responses of marandu palisadegrass, indicating that there is an ontogenetic effect on plant morphogenesis that should be considered further in future studies of this nature

A aceleração do ritmo de crescimento das plantas por meio da adubação nitrogenada altera a velocidade dos processos fisiológicos, atuando sobre o crescimento e a senescência, podendo refletir-se em alterações importantes sobre a estrutura do dossel. Avaliou-se a estrutura do dossel forrageiro de pastos de capim-marandu (Brachiaria brizantha) mantidos a 30 cm de altura por meio de lotação contínua e submetidos a ritmos de crescimento contrastantes de janeiro de 2007 a abril de 2008. Os distintos ritmos de crescimento foram criados por meio da utilização de adubação nitrogenada, segundo os tratamentos: sem adubação (controle), 150, 300 e 450 kg ha-1 de N. A aceleração do ritmo de crescimento dos pastos resultou em aumentos de densidade volumétrica de folhas e de colmos, refletindo em maior IAF e densidade volumétrica total em pastos submetidos aos ritmos de crescimento mais acelerados (adubados com 300 e 450 kg ha-1 de N) relativamente àqueles submetidos a ritmos de crescimento mais lentos (pastos não adubados e/ou adubados com 150 kg ha-1 de N). Variações em densidade volumétrica do material morto estiveram associadas a flutuações estacionais das condições climáticas, e não foram influenciadas pelos ritmos de crescimento avaliados. Na época da seca (outono/inverno e início de primavera), os pastos submetidos aos ritmos de crescimento mais acelerados apresentaram maior proporção de folhas no horizonte superior do dossel. Por outro lado, a estrutura do dossel não variou entre os ritmos de crescimento nas épocas de maior disponibilidade de fatores de crescimento (final de primavera e verão), indicando que quando o controle do processo de pastejo é feito de maneira eficiente, mudanças em estrutura são função basicamente de variações estacionais em condições climáticas e estádio fenológico das plantas.

Acceleration of the growth rhythm of plants using nitrogen fertiliser alters the rates of physiological processes like growth and senescence and may cause significant changes in sward structure, interfering with plant and animal responses. The objective of this experiment was to evaluate sward structure of marandu palisadegrass (Brachiaria brizantha) maintained at 30 cm under continuous stocking and subjected to contrasting rhythms of growth from January 2007 to April 2008. These were generated using or not nitrogen fertiliser, and comprised four experimental treatments as follows: control (non-fertilised), 150, 300 and 450 kg ha-1 of N. Acceleration of the growth rhythm of plants was associated with increases in leaf and stem bulk density, and resulted in larger LAI and total bulk density on swards subjected to faster (fertilised with 300 and 450 kg ha-1 of N) than those subjected to slower rhythms of growth (non-fertilised or fertilised with 150 kg ha-1 of N). Variations in dead material bulk density were associated with seasonal variations in climatic conditions, and were not influenced by growth rhythms. During autumn/winter and early spring (dry period of the year) swards subjected to faster, relative to those subjected to slower rhythms of growth, had larger proportion of leaves on the top horizons. On the other hand, sward structure did not vary among rhythms of growth at times of the year when there was no limitation in the availability of climatic growth factors (late spring and summer), indicating that when control of the grazing process is efficient, changes in sward structure are basically a function of seasonal variations in climatic growth conditions and phenological state of plants.

O objetivo deste trabalho foi avaliar a sobrevivência e a estabilidade da população de perfilhos em pastos de capim-marandu (Brachiaria brizantha) submetidos à lotação contínua e à adubação nitrogenada. Os tratamentos corresponderam a três doses de nitrogênio (150, 300 e 450 kg ha-1) mais o controle (sem adubação), e as unidades experimentais (piquetes de 1.200 m²) foram dispostas segundo um delineamento de blocos completos ao acaso, com quatro repetições. Foram avaliados mensalmente as taxas de sobrevivência, o balanço entre morte e aparecimento de perfilhos entre morte e aparecimento de perfilhos e o índice de estabilidade da população de perfilhos, de janeiro de 2007 a abril de 2008, em cinco épocas. A taxa de sobrevivência, o balanço entre morte e aparecimento e o índice de estabilidade da população de perfilhos variaram com as épocas do ano. Pastos que receberam 450 kg ha-1 de N apresentaram as menores taxas de sobrevivência no verão, contudo, mantiveram a estabilidade da população. Maiores doses de N possibilitam alcançar balanço positivo entre aparecimento e morte de perfilhos mais rapidamente no fim da primavera. O nitrogênio favorece a renovação de plantas e mantém a estabilidade da população de perfillhos desde que fatores como temperatura e precipitação não sejam limitantes.

The objective of this work was to evaluate the survival and stability of tiller population on marandu palisade grass (Brachiaria brizantha) swards subjected to continuous stocking and to fertilization with nitrogen. Treatments corresponded to three nitrogen doses (150, 300 and 450 kg ha-1) plus control (no fertilization), and the experimental units (1,200-m² paddocks) were placed according to a randomized complete block design, with four replicates. Survival rates, balance between tiller death and appearance and tiller population stability indexes were evaluated monthly from January 2007 to April 2008, in five seasons. Survival rates, balance between tiller death and appearance and the tiller population stability indexes varied according to the season. Swards fertilized with 450 kg ha-1 of N showed the lowest tiller survival rates during summers, but maintained population stability. Higher rates of N allow plants to achieve a faster positive balance between tiller death and appearance in late spring. Nitrogen favors plant turnover and keeps population stability as long as factors such as temperature and rainfall are not limiting.

O conceito de alvo de manejo tem sido utilizado recentemente para caracterizar estratégias de manejo do pastejo, mas sua eficiência em permitir controle e monitoramento da estrutura do dossel forrageiro questionada desde que corresponde a uma única característica estrutural, geralmente a altura do pasto. O objetivo deste experimento foi avaliar a estrutura do dossel forrageiro e seus padrões de variação ao longo do ano em pastos de capim-marandu mantidos a 30 cm sob lotação contínua e submetidos a ritmos de crescimento contrastantes de Janeiro 2007 a Abril de 2008. Os tratamentos corresponderam a três doses de aplicação de nitrogênio (150, 300 e 450 kg ha-1 de N) mais o controle (sem adubação), e foram alocados às unidades experimentais segundo um delineamento de blocos completos casualizados, com quatro repetições. Foram avaliadas massa de forragem, composição morfológica, índice de área foliar (IAF), ângulo da folhagem e interceptação luminosa dos pastos. O aumento das doses de aplicação de nitrogênio resultou em maior massa de forragem, proporção de folhas e colmos, e menor proporção de material morto. Estas modificações foram coerentes com o aumento registrado em IAF e a redução em ângulo da folhagem, embora não tenham resultado em variação na interceptação luminosa dos pastos. Apesar da grande amplitude das doses de nitrogênio avaliadas, houve um padrão comum de variação na estrutura dos pastos. No geral, as mudanças nas características estruturais dos pastos geradas pela amplitude de ritmos de crescimento avaliados foram pequenas, indicando que a altura do dossel correspondeu a uma forma eficiente de monitorar e controlar o processo de pastejo e a estrutura do dossel forrageiro.

The concept of sward target has been used recently to characterise grazing management practices, but its efficiency to monitor and control sward structure questioned since it corresponds to a single sward structural feature, usually sward surface height. The objective of this experiment was to evaluate sward structure and its patterns of variation throughout the year on continuously stocked marandu palisadegrass swards maintained at 30 cm and subjected to contrasting rhythms of growth from January 2007 to April 2008. Treatments corresponded to three nitrogen application rates (150, 300 and 450 kg ha-1 of N) plus the control (no N fertilisation), and were allocated to experimental units according to a complete randomised block design, with four replications. Sward herbage mass, morphological composition, leaf area index (LAI), foliage angle and light interception were evaluated. The increase in nitrogen application rates resulted in increased sward herbage mass, proportion of leaf and stem, and reduction in the proportion of dead material. These modifications were in line with the increase in LAI and reduction in foliage angle, although they did not modify sward light interception. Despite the wide range of nitrogen application rates used, there was a common pattern of variation in sward structure. Overall, changes in sward structural characteristics generated by the range of growth rhythms studied were small, indicating that sward height corresponded to an efficient way to monitor and control the grazing process and sward structure, and can be used to define targets of grazing management.