Effect of intensity of defoliation on regrowth of pasture

Abstract

A pasture association comprising short-rotation ryegrass, red clover, and white clover was subjected to three different intensities of defoliation by cutting down to 1, 3, and 5 in.A t 4-day intervals over a period of 32 days, nleasurements were taken of herbage d r y matter yield, the leaf area per unit area of ground, and the percentage of light penetrating to a level 1 in. above the ground surface.Where pasture was defoliated to 1 in., light interception was almost complete (95 per cent. or. over) approximately 24 days a f t e r cutting, whereas pastures defoliated to 3 in. and 5 in. intercepted almost all the incident light 16 and 4 days a f t e r cutting respectively.A t these stages of growth the leaf area was approximately 5 sq. f t per sq. f t of ground and the herbage yield approximately 1450 lb dry matter per acre, regardless of treatment.The r a t e of pasture growth increased until complete light interception was approached, and thereafter a n almost constant maximum rate was sustained.Leaf efficiency (the rate of increase of herbage dry weight per unit area of leaf) was greatly influenced by intensity of defoliation. Efficiency was initially lower following severe defoliation than following less severe treatment. I t increased rapidly to a nlaxiniurn and thereafter declined gradually. Maximum efficiency in the 3 in. and 5 in. cutting treatments was attained when maximum growth yate was first reached. F o r pasture defoliated to 1 in., i t reached a maximum level during the phase of accele~ating growth.

Altura do dossel e interceptação de luz em dosséis de leguminosas forrageiras

“…Em seu trabalho, Brougham (1956) demonstrou que quando o nível de IRFA atinge 95% da luz incidente, o IAF atinge um valor crítico, no qual a taxa de crescimento da cultura (TCC) estaria próxima de um valor máximo e portanto, o processo de rebrotação deve ser interrompido por corte ou pastejo. A altura do dossel é uma medida de fácil obtenção e a tentativa de relacioná-la com a IRFA pode facilitar atividades práticas de manejo dos pastos.…”

“…É empregada, com êxito, como adubação verde, para restauração de terras pobres; sendo, também, utilizada como forragem nos meses de inverno (VILELA, 1998). Quanto aos estudos do uso de forrageiras na produção animal, nos últimos anos, trabalhos estão sendo conduzidos com objetivo de relacionar a altura do dossel com a interceptação de radiação fotossinteticamente ativa pelo mesmo, pois se sabe que quando o dossel intercepta 95% da luz incidente, ele atinge a taxa de crescimento máximo da cultura (BROUGHAM, 1956) e o processo e rebrotação deve ser interrompido por corte ou pastejo.…”

Dynamics of forage accumulation in Elephant grass subjected to rotational grazing intensities

“…The most intense grazing (i.e., to a length of 30 cm) removes higher quantities of forage. Under these conditions, initial regrowth is slow, despite an improved light environment due to increases in the quantity and quality of light within the canopy (Brougham, 1956); this slow growth rate is due to a smaller amount of leaves, which results in a limited photosynthetic capacity after grazing (Parsons & Penning, 1988). Thus, carbon fixation and the production of organic compounds are reduced, which increases the time required to replenish the biomass (Parsons et al, 1983).…”

“…However, the defoliation intensity still needs to be determined. Using severe post-grazing heights can reduce photosynthesis rates in plants and increase apical meristem decapitation, which would increase the time required for the removed leaf area to recover (Brougham, 1956). However, using a severe (high) post-grazing height can also reduce intraspecific light competition by modifying the light environment in the canopy and promoting increased tissue and tiller renewal, thereby resulting in a younger population of tillers.…”

Estrutura do dossel, interceptação de luz e acúmulo de forragem em amendoim-forrageiro (<i>Arachis pintoi </i>Krapovickas &amp; Gregory cv. Belmonte) submetido a estratégias de pastejo rotativo

“…Segundo Verhagen et al (1963) e Pearce et al (1965), a produção de matéria seca é dependente da proporção da luz incidente que é interceptada e de sua eficiência de utilização, portanto dependente do IAF. Brougham (1956) descreveu mais detalhadamente a relação assintótica entre IL e IAF. Com aumento no IAF ocorre aumento da IL e da eficiência de uso da radiação fotossinteticamente ativa, o que ocasiona aceleração da taxa de crescimento em condições favoráveis de ambiente BLASER, 1968;HUMPHREYS, 1966).…”