Title: Is there flexibility in pre-grazing height targets in BRS Kurumi elephant grass?

 

Abstract: The use of the Leaf Area Index (LAI) as a management criterion for pastures under intermittent grazing is well established to ensure high net forage accumulation when regrowth is interrupted at a canopy height corresponding to 95% light interception (LI). Despite this, studies demonstrate the ability of lowgrowing forage plants to make adjustments that maintain forage production at heights lower than the critical LAI threshold. These adjustments vary according to the limits of the species' phenotypic plasticity and affect tiller size and population/tissue flow, directly impacting the plant's persistence mechanisms. However, for tall, tuft-forming plants, the existence of such homeostatic mechanisms is unknown. The objective of this study was to determine the existence of variation in pre-grazing management heights where forage accumulation does not change in a tuft-forming plant, using the elephant grass BRS Kurumi (Cenchrus purpureus Schumach) as a model plant. Thus, an experimental protocol was conducted in elephant grass pastures (cv. BRS Kurumi) managed with three pre-grazing canopy heights (50, 65, and 80 cm) and the same defoliation proportion of 50% of the initial heights (resulting in postgrazing heights of 25, 32, and 40 cm, respectively) over two years (2021-2023). The experimental design consisted of a randomized complete block design, with three replications, totaling nine experimental units (145 m² paddocks). Forage mass evaluations were carried out as pastures reached the target management height through sampling in 1 m² metal frames, allowing the estimation of pasture botanical components and LAI. Every 21 days, newly emerged and surviving tillers were identified and counted in two tussocks per experimental unit. The data were grouped by season and subjected to variance analysis, with means estimated by LSMEANS of INFOSTAT and tested by Fisher's LSD test at 5% significance. Adjustments in tiller population/tissue flow and size were observed at the lower management heights; however, maintaining forage production was only possible at canopy heights of 65 cm or higher. In pastures managed at 50 cm, the homeostatic mechanism's action failed to compensate for forage production, possibly due to the species' limited phenotypic flexibility, which compromises pasture persistence in the long term.

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Keywords: Canopy management, homeostasis, tillers, tuft-forming grasses.

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Author: Valentina Ylluyanka Moncada

Leader: André Fischer Sbrissia

Thesis (Doctors in Animal Science)