Effects of postgrazing residue on morphogenetic and structural characteristics of Tifton 85 pastures

Abstract

The ideal time to start grazing is when pastures reach 95% light interception. The use of residual leaf area index (rLAI) to time the interruption of grazing under intermittent grazing has recently been studied in forage species in different climatic conditions in Brazil. However, studies evaluating the formation and development of leaves and tillers through morphogenetic and structural variables in functional rLAI are still lacking for Tifton 85 pastures. Therefore, the objective of this study was to evaluate the effects of varying rLAI in successive grazing cycles on morphogenetic and structural characteristics of Tifton 85 pasture grazed intermittently by sheep. Morphogenetic and structural characteristics were evaluated in three grazing cycles under three rLAI conditions (0.8, 1.6, and 2.4). The regrowth interval (time taken to return to 95% light interception) of pastures increased from 21.33 to 29.66 days with decreasing rLAI. The leaf appearance rate increased at a rate of 0.02 leaves tiller -1 day -1 and the number of live leaves per tiller increased by 0.41 with decreasing rLAI. Phyllochron, leaf elongation rate, final leaf length, leaf senescence rate, and stem elongation rate decreased linearly with decreasing rLAI. The number of live leaves per tiller was lower (7.97) in the third grazing cycle, probably owing to the higher senescence rate observed that same cycle, while the other variables had higher values. The 2.4 rLAI condition promotes excessive stem elongation, reduced leaf appearance, lower number of live leaves per tiller, and increased senescence of leaves, while the 0.8 and 1.6 rLAI conditions promote desirable morphogenetic and structural characteristics, which correlate directly with forage quality. In order to avoid excessive forage losses, grazing must occur preferentially by the end of March, when climatic conditions still support the appropriate development of the plants. Key words: Grazing cycles. Leaves appearance. Light interception. Residual leaf area index. Stem elongation. ResumoO momento de iniciar o pastejo quando os pastos atingem 95% de interceptação luminosa e de interrupção do pastejo por meio de índices de área foliar residual (IAFr), em situação de pastejo intermitente, recentemente vem sendo estudado em espécies forrageiras em distintas condições climáticas do Brasil, porém, pesquisas avaliando a formação e desenvolvimento de folhas e perfilhos por meio das variáveis morfogênicas e estruturais em função de IAFr são ainda inexistentes em pastos de Tifton 85. Por isso,

Anatomical, morphogenic and structural characteristics of Xaraés palisade grass under grazing

“…The linear increase in LSR with increasing pasture rLAI (Table 2) is due to increased pasture height, which accentuates the shading caused by the upper canopy layers over the lower layers. Silva et al (2016b) also observed the same response pattern for LSR in Tifton 85 pastures managed under rLAI 0.8, 1.6 and 2.4, with values ranging from 0.33 to 0.46 cm tiller -1 day -1 . The LLS ranged from 37.10 to 50.44 days with increasing pasture rLAI suggesting greater tissue renewal under more intensive grazing conditions.…”

“…In pastures managed up to rLAI 1.8 the LER increased due to higher stem elongation, which provide longer time for leaf emergence resulting in higher LER (Silva et al 2013). This response pattern is common in tropical grasses when managed under different grazing intensities, i.e., grazing heights (Sbrissia et al 2018;Oliveira et al 2020) or rLAI (Silva et al 2016b). Another justification for this response pattern is due to the lower removal of expanding leaves and stem during grazing in pastures under lower grazing intensities.…”

“…Coupled with information on the leaf anatomy and morphogenetic characteristics, studies involving light interception by the sward and residual leaf area index as predictors of frequency and grazing intensity respectively, have demonstrated the importance of these variables regard to the growth of plants and responses to defoliation. Regrowth ability, in addition help to define the best moment for the insertion and removal of animals into and from pastures under intermittent grazing (Galzerano et al 2013;Galzerano et al 2015;Silva et al 2016a;Silva et al 2016b;Silva et al 2019). Thus, we need to understand how the grazing intensity in intermittent grazing can change the morphogenesis and leaf anatomy of grasses in order to interfere in the degradability of tissues in the animals' rumen.…”