Abstract
Leaf area index is the main sward characteristic related to the processes of light interception and competition in plant communities. The objective of this experiment was to quantify and evaluate the composition of the leaf area on tillers of marandu palisadegrass (Brachiaria brizantha cv. Marandu) subjected to strategies of intermittent stocking. The experiment was carried out in Piracicaba, state of São Paulo, Brazil, from October/2004 to December/2005. Swards were grazed at 95 and 100% canopy light interception (LI) to post-grazing heights of 10 and 15 cm, following a 2 ' 2 factorial arrangement with four replications in a randomised complete block design. Estimates were made of sward leaf area index, site filling, specific leaf area and the dimensionless ratio between tiller leaf area and volume (R), as well as the relative contribution of basal and aerial tillers to these variables. In early spring, values of leaf area index and specific leaf area were low when compared to the other seasons, and swards grazed at 95% LI presented higher site filling and specific leaf area than those grazed at 100% LI. This resulted in higher tillering activity and increase in leaf area index in late spring, indicating quick recovery and early return of swards grazed at 95% LI to growing conditions. Aerial tillers corresponded to an important morphological adaptation of marandu palisadegrass to increase its competitive ability. Treatment 100/10 resulted in the highest and 95/15 in the lowest R values throughout the experiment, suggesting an allometric pattern of growth of tillers during regrowth in order to compensate low tiller population and optimise the leaf area index. Grazing management practices can benefit from this knowledge by promoting ideal sward conditions to maximise and accelerate growth.
Highlights
Leaf area index (LAI), defined as leaf surface area per unit soil surface area (Watson, 1947), is the main factor influencing light interception and the dynamics of regrowth of swards subjected to intermittent stocking (Chapman & Lemaire, 1993)
Swards grazed at 95% light interception (LI) had larger Leaf area index of aerial tillers (LAIa) in early spring 2004 and lower in late spring 2004 in relation to those grazed at 100% LI, with no differences between LI treatments during the remaining seasons of the year (Figure 3b)
The fact that swards managed at 95% had Leaf area index of basal tillers (LAIb) 25% lower in early spring 2004, 23% higher in late spring 2004 and 20% lower in summer 2005 in relation to those managed at 100% LI (Figure 3a), probably occurred because swards managed at 95% LI started to be grazed earlier and at a shorter grazing interval than those managed at 100% LI (Table 1)
Summary
Leaf area index (LAI), defined as leaf surface area per unit soil surface area (Watson, 1947), is the main factor influencing light interception and the dynamics of regrowth of swards subjected to intermittent stocking (Chapman & Lemaire, 1993). LAI is considered the principal sward structural component sensible to varying defoliation conditions and intensities (Lemaire & Chapman, 1996) It has high correlation with both plant and animal responses (Sbrissia & Da Silva, 2001), being, for that reason, essential for understanding the herbage accumulation process and planning grazing management practices (Da Silva & Nascimento Jr., 2007). Sward LAI is a result of plant morphogenetic responses to the environment and management strategies (Lemaire & Chapman, 1996) These responses provide plants with plasticity and adaptive ability, which may be assessed by the R ratio (tiller leaf area3/2/tiller volume), defined by Sackville-Hamilton et al (1995) to evaluate morphogenetic variations in tillers as they adjust to grazing management practices imposed and varying climatic conditions (Matthew et al, 1995)
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