Acúmulo de forragem e estrutura dos pastos das cultivares BRS Zuri e BRS Quênia (Megathyrsus maximus) sob manejo rotacionado

Abstract

Under the hypothesis that there is a difference in pasture structures and forage accumulation of cultivars BRS Zuri and BRS Quênia, the objective was to evaluate them when submitted to rotational stocking by dairy cows. The experiment was conducted at Embrapa Cattle of Milk under a randomized complete block design with two treatments (BRS Zuri and BRS Quênia) and three replicates, from 12/09/2016 a 08/21/2017 and from 11/12/2017 to 04/05/2018. Were evaluated: canopy height (pre and post-grazing), percentage of lowering of pastures (%L, forage mass (FM) and morphological composition: dry masses and percentages of leaf blades (DMLB and %LB), stems (DMS and %S) and dead material (DMDM and %DM); the forage bulk density (FBD), leaf: stem ratio (LSR), tillers population density (TPD), forage accumulation (FA) and forage accumulation rate (FAR) variables were evaluated under “Proc Mixed” of SAS® and the Fischer and Tukey tests (p<0,10). Higher values of pre and postgrazing height were observed for BRS Zuri, while higher %C and TPD were obtained for BRS Quênia in 2016/2017 and 2017/2018. There was an additional cycle of grazingduring 2016/2017 and higher values of FBD, DMLB and LSR in autumn 2016/2017, and little variation in FBD, DMLB, TPD and FAR in the grazing cycles of 2017/2018 for the cultivar BRS Quênia. Higher MF was obtained for BRS Zuri in 2016/2017 and, in 2017/2018, there was no cultivar effect for this variable. There was a grazing cycle effect for FBD and DMLB in 2016/2017, with higher FBD values during the autumn, and DMLF for BRS Quênia in the same season. In 2017/2018 the lowest values of FBD were obtained for BRS Zuri in the middle of summer and for BRS Quênia at the end of this season, higher DMLB was obtained for BRS Quênia in the autumn. There was a grazing cycle effect for DMS, DMDM, %DM and %S, with higher values during the autumn 2016/2017 cycles, and lower DMS and DMDM during 2017/2018. The FA varied according to cultivar and grazing cycle interaction in 2016/2017, with a higher value for BRS Quênia during the summer, and only with the grazing cycle in 2017/2018, with a lower value in early summer. The FAR varied with the grazing cycle in 2017/2018, with increase during summer and reduction during autumn and winter, and as a function of the cultivar and grazing cycle interaction in 2017/2018, with higher values at the end from spring and mid-summer to BRS Zuri. The cultivars present structural differences of their canopies and are indicated for use in intensive systems of milk cattle under rotational management of pastures during the summer and especially in the autumn, with highlight for BRS Quênia in this season.