Canopy Structure of Marandu Palisadegrass Pasture Under Rotational Stocking Strategies.

Marandu palisadegrass is the most common pasture in Brazil, occupying about 50% of the cultivated pasture areas. As a tufted perennial grass, the control of sward structure under grazing is important for increasing forage quality, efficiency of utilization and the productivity. The objective of this study was to evaluate the effect of two rest periods on the structural traits of Marandu palisadegrass pasture. Two rest periods were studied: a fixed rest period of 30 days (RP30) and a variable rest period based on canopy light interception (LI) of 95% (LI95). In both treatments, grazing lasted three days with four Holstein x Zebu cows per paddock aiming at a post-graze stubble of 20-25 cm. Average paddock size was 850 m². Data were collected in spring-summer of 2011-2012, in five grazing cycles. The experimental design was randomized blocks with four replications and data were analyzed as repeated measures (grazing cycles) using the Mixed Procedure of SAS®. Means were estimated using the "LSMEANS" command and comparisons made with Student t test with a 10% significance level. The mean grazing interval for LI95 ranged from 18 to 30 days, averaging 23 days. The average canopy height was 36 and 42 cm, respectively for LI95 and RP30. The leaf-stem ratio was higher for LI95 in almost all grazing cycles with an average value of 1.69 versus 1.27 for RP30. The leaf percentage in the pre-grazing forage mass reduced over the season in both treatments. However, this reduction was more pronounced for  RP30, from 54% in cycle 1 to 31% in cycle 4, while in LI95 the decrease was from 55% to 49%, respectively, for cycles 1 and 4. The adoption of morphophysiological criteria for interrupting the rest period improves the structure of Marandu palisadegrass pasture.