Frequencies and intensities of defoliation in Aruana Guineagrass swards: accumulation and morphological composition of forage

Guilherme Doneda Zanini,André Fischer Sbrissia,Gabriela Trevisan Santos

doi:10.1590/s1516-35982012000400011

Guilherme Doneda Zanini, André Fischer Sbrissia + Show 1 more

Open Access

https://doi.org/10.1590/s1516-35982012000400011

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Abstract

The objective of this study was to assess the accumulation and morphological composition of forage in Aruana Guineagrass (Panicum maximum cv. Aruana) swards subjected to intermittent stocking with sheep. Experimental treatments when grazing was introduced included low (95%) and high (98%) incident light interception and low (10 cm)- and high (15 cm)-residue height and were allocated to experimental units (196 m2 fenced areas) in a completely randomized 2 × 2 factorial arrangement with three replicates. Treatments were imposed between January and May 2009. More frequent grazing cycles (95% light interception) resulted in better control of stem elongation, lower proportion of dead plant material and invasive plants, and higher proportions of leaf blades in the grazing strata, compared with less frequent grazing cycles (98% light interception). Grass managed with 95% light interception combined with 10 and 15 cm post-grazing height and grass managed at 98% light interception combined with 15 cm post-grazing height did not show differences in forage accumulation rate. These results indicate that more frequent (30 cm pre-grazing height) and less severe (15 cm post-grazing height) grazing cycles provided animals with high leaf blade mass and low stem mass forage.

Highlights

The spatial structure of swards has a significant influence on animal grazing behavior because the height and availability of preferred components have clear effects on instantaneous intake rate and bite mass (Amaral, 2009)
Because the interval between grazing cycles was defined as a function of two light interception levels, the number of grazing cycles was expected to vary between the treatments
During the pre-grazing period, forage mass was only affected by the time of year (P

Summary

Introduction

The spatial structure of swards has a significant influence on animal grazing behavior because the height and availability of preferred components have clear effects on instantaneous intake rate and bite mass (Amaral, 2009). The structure of the grass sward is determined by the processes of plant decline and senescence along with defoliation, which depends on grazing management (Chacon & Stobbs, 1976). This, in turn, influences the responses of plants and animals (Hodgson, 1985; Chapman & Lemaire, 1993) because it determines the patterns of light interception and access by animals (Laca & Lemaire, 2000). Grazing management techniques used to optimize forage production in swards must seek to reach a compromise between the need to retain sufficient leaf area for photosynthesis and the need to remove leaf tissue before senescence (Hodgson & Da Silva, 2002) to meet established forage production goals (Parsons & Penning, 1988). The net forage accumulation of a species results from the difference between gross weight increase due to new tissue formation and reduction caused by senescence

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