Use of a model to optimize the interaction between frequency and severity of intermittent defoliation and to provide a fundamental comparison of the continuous and intermittent defoliation of grass

Abstract

A previously described model of grass growth was used to analyse the effect of the severity of defoliation and the duration of the subsequent regrowth on the overall balance between photosynthesis, gross tissue production and leaf death and so on the amount that could be harvested/consumed per hectare under intermittent defoliation. Maximum yield per hectare was shown to be achieved whenever the fluctuations in LAI during regrowth and defoliation led lo the same low average LAI that was previously shown to give maximum yield (amount harvested/consumed per hectare) under continuous grazing. Thus, it is suggested that production under both continuous and intermittent defoliation may best be characterized, and diverse managements may be rationalized, on the basis of the average sward state, the average achieved. The analysis leads us to reconsider some widely held concepts of the growth and utilization of grass applied in both agronomic and ecological theory, and the provision of practical guidelines for management.

Sward structure and herbage yield of rotationally stocked pastures of 'Marandu' palisadegrass [Brachiaria brizantha (A.Rich.) Stapf] as affected by herbage allowance

“…In a companion study performed on the same pastures (Peternelli, 2003), mean tiller population densities at the end of the 2003 grazing season were 1,658, 1,413, 1,217 and 1,087 tillers m -2 for 5, 10, 15 and 20%-HAL. Under continuous stocking, both herbage production and utilization seem to be linked to a specific sward condition, such as LAI or LI, and in practice, these structural guidelines can often be "translated" to sward height (Parsons et al, 1983). Results of the present study, however, suggest that the relationship between LI and sward height can change over time, and that at least under intermittent defoliation regimens this association should be used with caution, as already pointed out by Parsons et al (1988) and Busque & Herrero (2001).…”

“…It is not clear, however, whether these associations hold true in swards under intermittent defoliation, as the dynamics of successive cycles of defoliation followed by regrowth make for a wide range of sward conditions over short periods of time. It is uncertain, for example, whether LAI and LI can be accurately estimated by measurements of sward height in intermittently grazed swards (Parsons et al, 1988). The diverse conditions of sward structure produced by manipulation of HAL and regrowth period can help identify relationships between sward height and LI that support new management guidelines for palisadegrass under intermittent grazing.…”

“…In steady-state stands, such as in continuously stocked pastures, the role of sward structure as it relates to canopy LI and to leaf area index (LAI) is recognized as key in establishing cause-effect relationships involving agronomic responses to management (Parsons et al, 1983). It is not clear, however, whether these associations hold true in swards under intermittent defoliation, as the dynamics of successive cycles of defoliation followed by regrowth make for a wide range of sward conditions over short periods of time.…”

Modificações na estrutura vertical de pastos de capim-xaraés sob lotação intermitente por bovinos

“…4). A interceptação de luz pelo dossel, fator chave na realização da fotossíntese, no crescimento e no desenvolvimento das plantas, depende não somente do índice de área foliar do pasto, mas das propriedades ópticas das folhas, assim como do seu arranjo espacial no centro do dossel (Parsons, 1988 No ano 1, o efeito dos CP foi quadrático (P<0,05), com valores de 10,85% no CP 1 e de 18,95 no CP 4. Já no ano 2, houve efeito (P<0,05) linear, com valores de 19,27% no CP 1 e de 27,0% no CP 4, confirmando o exposto acima sobre a aceleração do processo de senescência sob condições menos favoráveis ao desenvolvimento das plantas.…”

Compensação tamanho/densidade populacional de perfilhos em pastagens de Cynodon spp.

“…Parsons et al (1988) compararam efeitos de métodos aparentemente antagônicos de manejo da desfolha (i.e. lotação contínua e lotação rotacionada) sobre alguns parâmetros fisiológicos relacionados com os processos responsáveis pelo acúmulo de forragem e obtiveram resultados similares, indicando a existência de mecanismos compensatórios que tendem a anular possíveis vantagens comparativas de um método sobre outro.…”