Defoliation intensity and leaf area index recovery in defoliated swards: implications for forage accumulation

Abstract

This study evaluated the leaf area index (LAI) recovery mechanisms and forage accumulation rates on the regrowth of different grass species subjected to different defoliation intensities. For that purpose, plots of Pennisetum clandestinum (kikuyugrass), Lolium multiflorum (annual ryegrass), and Avena strigosa (black oats) were defoliated from 20 to 80 % of their initial heights (25, 20, and 25 cm, respectively). At different increments in height, forage samples were collected to ground level and used to estimate tiller population density (TPD), leaf area per tiller (L A), and forage mass. From these data, we calculated the leaf area index (LAI), average leaf area index (aLAI), and average and instantaneous forage accumulation rate (FAR and IFAR, respectively). Data were plotted over time (days) to describe LAI recovery and forage accumulation rates. As the defoliation intensity increased, greater canopy heights were needed for pastures to achieve their maximum forage accumulation rates, which required longer regrowth intervals. The need for high tiller recruitment after defoliation, which delayed canopy LAI recovery, seemed to be one of the main cause. Thus, grazing management strategies that involve costly tiller recruitment could decrease both overall forage production and sward persistence over time. However, the plant ability to recover LAI after successive intense defoliations seems to be species-dependent and related to their phenotypic plasticity.

Fatores que afetam as características morfogênicas e estruturais de plantas forrageiras

“…A amplitude térmica ambiental do ecossistema de pastagem provoca efeitos na produção de biomassa do dossel forrageiro, causando mudanças na dinâmica do acúmulo de forragem (Andrade et al, 2016 O desenvolvimento e crescimento do dossel forrageiro é controlado, principalmente, pela produção de folhas, órgão responsável por absorver a energia solar que chega à parte superior do dossel. Em vista disso, com o aumento do índice de área foliar (IAF), eleva-se a interceptação da radiação fotossinteticamente ativa (RFA) do dossel forrageiro concomitantemente ao acúmulo de massa seca da planta forrageira (Martins et al, 2021).…”

Ammonium sulfate rates affect the Structural Characteristics, Biomass and Crude Protein of BRS Tamani Grass

“…For tropical pastures, an increase in the number of tillers is generally related to the stress exerted by the effects of the intensity and frequency of defoliation on the forage canopy, leading to a change in the growth strategy of the tillers to efficiently enhance the leaf area recovery. This phenomenon is known as 'site filling', in which the leaf length of the tiller reduces (third cut; Table 1) and, as an alternative way of increasing the leaf area index in the forage canopy, the tiller community significantly increases (Barbosa et al, 2011;Martins et al, 2020;Veras et al, 2020a).…”

Nitrogen nutritional status in perennial grasses under defoliation: Do stubble height and mixed cultivation matter?

“…The stubble height was selected based on Martins et al. (2021), who found that, in general, defoliation intensities greater than 50% are detrimental to herbage accumulation. Canopy height was monitored at 20 points per plot using an acetate sheet and ruler.…”

“…Recent grazing management studies have recommended moderate/lenient defoliations as a means of maximizing forage production ( Sbrissia et al., 2018; Martins et al., 2021), herbage intake ( Mezzalira et al., 2014; Schmitt et al., 2019), and individual animal performance ( Difante et al., 2010; Euclides et al., 2018). This strategy results in a greater stubble mass remaining, composed mainly of structural and senescent tissues ( Zanini et al., 2012; Euclides et al., 2018).…”