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

Clóvis David Medeiros Martins,Daniel Schmitt,Tiago Miqueloto,André Fischer Sbrissia,Paulo Gonçalves Duchini

doi:10.1590/1678-992x-2019-0095

Clóvis David Medeiros Martins, Daniel Schmitt + Show 3 more

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https://doi.org/10.1590/1678-992x-2019-0095

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Journal: Scientia Agricola	Publication Date: Jan 1, 2021
Citations: 18	License type: CC BY 4.0

Affiliation: Universidade do Estado de Santa Catarina

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 (LA), 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.

Highlights

The critical leaf area index ([LAI]; Brougham, 1958) has been suggested as the upper limit to interrupt regrowth of pastures under intermittent stocking method (Korte et al, 1982; Carnevalli et al, 2006; Sbrissia et al, 2018)
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
The time required for canopies to reach IFARmax and FARmax rose as defoliation intensity increased (Figure 1A-F); kikuyugrass did not reach either FARmax or IFARmax when defoliated at 70 %, since the protocol used for this species comprised assessments of only up to 25 cm (Table 4)

Summary

Introduction

The critical leaf area index ([LAI]; Brougham, 1958) has been suggested as the upper limit to interrupt regrowth of pastures under intermittent stocking method (Korte et al, 1982; Carnevalli et al, 2006; Sbrissia et al, 2018). According to Chapman (2016), intense defoliations would result in longer regrowth intervals, which could reduce total forage production. The LAI recovery after defoliation occurs through leaf growth from remaining tillers and/or the emergence of new tillers (Lemaire and Chapman, 1996). High defoliation intensities can stimulate initial LAI increments through the recruitment of new tillers due to the improved light quality reaching the plant base (Gautier et al, 1999) and apex meristem decapitation (McSteen, 2009). Forage plants are incapable to maintain a high growth potential after defoliation, despite the possibility of mobilizing carbohydrate reserves and of changes in a specific leaf area (Irving, 2015; Chapman, 2016)

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