Thursday, November 8, 2007 - 9:30 AM
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Sward Structure and Herbage Accumulation on Pastures of Xaraes palisadegrass [Brachiaria brizantha cv. Xaraes] in Response to Rotational Grazing Strategies.

Carlos G. Pedreira, Universidade of Sao Paulo, Dept. Zootecnia ESALQ-USP, Av. Padua Dias 11, Piracicaba, 13418-900, Brazil and Bruno C. Pedreira, Universidade de Sao Paulo, Dept. Zootecnia ESALQ-USP, Av. Padua Dias, 11, Piracicaba, 13418-900, Brazil.

Dry matter yield is ultimately dependent upon the efficiency with which light is captured and how light is distributed within the canopy profile. Use of incoming solar radiation is affected by three main factors: light intensity, leaf spatial distribution, and leaf optical properties. Management strategies have a strong impact on grazing systems efficiency and affect sward structure by altering accumulation dynamics and plant part composition in accumulated forage. The objective of this research was to characterize the agronomic performance of Xaraes palisadegrass [Brachiaria brizantha cv. Xaraes] as a response to rotational grazing, according to schedules based either on canopy light interception (LI) or calendar days. Paddocks grazed whenever canopy LI reached 95% were defoliated six times during the 153 days of the experimental period, whereas those grazed at 100% LI and every 28 days were defoliated four and five times respectively. Swards managed at 95% LI and 28-d, despite having similar mean leaf area index (LAI), reached different pregraze heights. Postgraze sward height was 14.6 cm, close to the planned target stubble height (15 cm) and that corresponded to a mean 0.73 LAI, 42% LI and 65.2º leaf angles. At pregraze leaf angles were not affected by grazing management (mean = 42º). Swards managed at 95% LI were 29.5 cm tall at pregraze and when managed at 100% LI, mean height reached 41.6 cm. Sward height and LI were highly correlated (r = 0.84) across treatments, suggesting the effectiveness of sward height as a practical grazing management guide. Sward height was also positively correlated (r=0.92) with LAI. Grazing strategies differed in total forage yield during the warm rainy season. Grazing at 100% LI resulted in longer paddock rest periods and highest seasonal forage yield (22,760 kg DM ha-1) compared to the other two treatments (mean = 17,700 kg DM ha-1).