Lilian Elgalise Techio Pereira

Morphogenesis on age categories of tillers in marandu palisadegrass

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 ( 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

Structural characteristics of marandu palisadegrass swards subjected to continuous stocking and contrasting rhythms of growth

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.

Estabilidade da população de perfilhos de capim-marandu sob lotação contínua e adubação nitrogenada

O objetivo deste trabalho foi avaliar a sobrevivencia e a estabilidade da populacao de perfilhos em pastos de capim-marandu (Brachiaria brizantha) submetidos a lotacao continua e a adubacao nitrogenada. Os tratamentos corresponderam a tres doses de nitrogenio (150, 300 e 450 kg ha-1) mais o controle (sem adubacao), e as unidades experimentais (piquetes de 1.200 m2) foram dispostas segundo um delineamento de blocos completos ao acaso, com quatro repeticoes. Foram avaliados mensalmente as taxas de sobrevivencia, o balanco entre morte e aparecimento de perfilhos entre morte e aparecimento de perfilhos e o indice de estabilidade da populacao de perfilhos, de janeiro de 2007 a abril de 2008, em cinco epocas. A taxa de sobrevivencia, o balanco entre morte e aparecimento e o indice de estabilidade da populacao de perfilhos variaram com as epocas do ano. Pastos que receberam 450 kg ha-1 de N apresentaram as menores taxas de sobrevivencia no verao, contudo, mantiveram a estabilidade da populacao. Maiores doses de N possibilitam alcancar balanco positivo entre aparecimento e morte de perfilhos mais rapidamente no fim da primavera. O nitrogenio favorece a renovacao de plantas e mantem a estabilidade da populacao de perfillhos desde que fatores como temperatura e precipitacao nao sejam limitantes.

Sward structure of marandu palisadegrass subjected to continuous stocking and nitrogen-induced rhythms of growth

A aceleracao do ritmo de crescimento das plantas por meio da adubacao nitrogenada altera a velocidade dos processos fisiologicos, atuando sobre o crescimento e a senescencia, podendo refletir-se em alteracoes 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 lotacao continua 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 utilizacao de adubacao nitrogenada, segundo os tratamentos: sem adubacao (controle), 150, 300 e 450 kg ha-1 de N. A aceleracao do ritmo de crescimento dos pastos resultou em aumentos de densidade volumetrica de folhas e de colmos, refletindo em maior IAF e densidade volumetrica total em pastos submetidos aos ritmos de crescimento mais acelerados (adubados com 300 e 450 kg ha-1 de N) relativamente aqueles submetidos a ritmos de crescimento mais lentos (pastos nao adubados e/ou adubados com 150 kg ha-1 de N). Variacoes em densidade volumetrica do material morto estiveram associadas a flutuacoes estacionais das condicoes climaticas, e nao foram influenciadas pelos ritmos de crescimento avaliados. Na epoca da seca (outono/inverno e inicio de primavera), os pastos submetidos aos ritmos de crescimento mais acelerados apresentaram maior proporcao de folhas no horizonte superior do dossel. Por outro lado, a estrutura do dossel nao variou entre os ritmos de crescimento nas epocas de maior disponibilidade de fatores de crescimento (final de primavera e verao), indicando que quando o controle do processo de pastejo e feito de maneira eficiente, mudancas em estrutura sao funcao basicamente de variacoes estacionais em condicoes climaticas e estadio fenologico das plantas.

Structural characteristics of tiller age categories of continuously stocked marandu palisade grass swards fertilized with nitrogen

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.

Carbon and nitrogen reserves in marandu palisade grass subjected to intensities of continuous stocking management

Plant organic reserves and sward leaf area index (LAI) influence plant growth, persistency and herbage accumulation in grazed swards. The present study was conducted to describe patterns of variation in herbage accumulation and carbohydrate and nitrogen (N) reserves in shoot and root of marandu palisade grass subjected to intensities of continuous stocking management throughout the year. Treatments corresponded to four levels of grazing intensity – severe (S), severe/moderate (S/M), moderate (M) and lenient (L) – and were implemented in the field using bands of sward surface height (SSH – 10, 20, 30 and 40 cm ± 10%, respectively) maintained through continuous stocking and variable stocking rate. Total N concentration was higher in the shoot relative to the root compartment during autumn, early and late spring. On the other hand, the concentration of non-structural carbohydrates (NSC) and soluble N was higher in the root compartment, regardless of grazing intensity and season of the year. When taking into account the pool of C and N reserves, the shoot compartment represented the main storage organ, since it corresponded to the largest pool of NSC (averages of 0·102 ± 0·0038 and 0·201 ± 0·0088 kg/m² for root and shoot, respectively) and soluble N (averages of 2·7 ± 0·26 and 5·3 ± 0·59 kg/m² for root and shoot, respectively). During late spring, the time of active plant growth, there was a clear contrast in herbage accumulation and sward LAI among grazing intensities, particularly between the severe and lenient grazing treatments. The results show that even with larger pools of soluble N and NSC in the shoot compartment, herbage accumulation was limited by the reduced leaf area of swards subjected to the severe grazing treatment, indicating that under continuous stocking growth seems to be sustained by current assimilates instead of organic reserves. Therefore, targets of grazing management for maximizing herbage accumulation throughout the year should provide adequate combinations between quantity and quality of sward leaf area. This condition was obtained in the severe/moderate and moderate grazing intensities, and corresponded to sward heights between 20 and 30 cm for marandu palisade grass.