Stem dynamics and stability index in five Urochloa cultivars in semi-arid conditions

Abstract

The objective of this research was to evaluate the effects of temperature and rainfall on stem dynamics and the stability index in 5 cultivars of the genus Urochloa under semi-arid conditions. The cultivars evaluated were Camello I, Camello II, Mulato II, Convert 330 and Cobra, in a completely randomized design with 6 replicates. The temperature and precipitation during the evaluation period stimulated stem dynamics (P<0.05). Cobra and Mulato II cultivars presented densities higher than 4,000 stems/m2 on average, as a response to the higher number of tillers (769 and 718/ m2, respectively) even with a relatively high stem mortality (336 and 449 stems/m2, respectively). Having the maximum values of accumulated heat units during periods of little or no precipitation compromised the sward stability index (values <1.0). Cuts during the frost period (November) caused a 20 \% increase in the mortality rate and, consequently, a decrease in the stability index of up to 0.83. The prevalent environmental conditions along with the continuous growth resulted in losses of stability of Urochloa cultivars, due to a lower tillering rate with respect to stems acute accent mortality rate.