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

Abstract

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. Key words: Brachiaria brizantha, nitrogen, sward structure, sward height, grazing management Características estruturais de pastos de capim-marandu submetidos à lotação contínua e ritmos de crescimento contrastantes RESUMO: 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 ...

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

“…In spite of the small variation in spatial distribution of the morphological components along the vertical profile of the swards, those subjected to the slower rhythms of growth (non-fertilised or fertilised with 150 kg ha -1 of N) had a more vertical architecture (higher foliage angle) than those subjected to faster rhythms of growth (fertilised with 300 and 450 kg ha -1 of N) (Mesquita et al, 2010). Modifications in foliage angle are a result of variations in the arrangement of morphological components in both vertical and horizontal dimensions of the sward, consisting in an important structural response, particularly to competition for light.…”

“…Although LBD and SBD increased with the increase in growth rhythm of plants, the proportion between these two morphological components in sward herbage mass did not vary significantly, with values of the LBD:SBD ratio of 0.72, 0.70, 0.68 and 0.74 for non-fertilised and swards fertilised with 150, 300 and 450 kg ha -1 of N, respectively. In a concomitant experiment in the same area, Mesquita et al (2010) found that the acceleration of the growth rhythm of plants by nitrogen application triggered an important plastic response in terms of herbage accumulation characterised by proportional increments in the proportion of leaf and stem in sward herbage mass and small changes in sward structure, suggesting a "compensating mechanism" of sward responses to variations in growth rhythm when subjected to steady state management conditions.…”

“…Gastal and Nelson (1994) commented that nitrogen can generate a three to four fold increase in leaf elongation rate (LER), suggesting that this is the main morphogenetic response to nitrogen fertiliser application. Although LER is the characteristic determining acceleration of the growth rhythm of plants, tiller population density (TPD) plays an important role in increasing herbage bulk density and herbage mass on nitrogen fertilised swards (Fagundes et al, 2006;Mesquita et al, 2010). Nitrogen application increases the proportion of growing tillers and, consequently, augments the tillering process (Cruz and Boval, 2000).…”

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

“…6 to Jul.30, 2007) and another during summer 2008(Feb. 22 to Mar. 19, 2008, which were periods of low and high growth rates of plants, respectively (Mesquita et al, 2010). In order to perform this kind of evaluation, it was necessary to know the time of appearance of each tiller generation, which was the reason why measurements of this experiment were performed on tillers tagged every 28 days following a protocol for evaluating tiller dynamics and demography in a concomitant experiment in the same experimental area (Caminha et al, 2010).…”

Frequencies and intensities of defoliation in Aruana guineagrass swards: morphogenetic and structural characteristics

“…The results available for Brazilian conditions, obtained in recent years for tropical forage plants, both under continuous (Mesquita et al, 2010;Pereira et al, 2010) and intermittent stocking conditions , in experiments characterized by strict control of the forage sward structure have shown high potential for forage production and animal performance. The objective of this experiment was to study the effects of different frequencies and intensities of grazing on the morphogenetic and structural characteristics of tillers on pastures of Panicum maximum Jacq.…”