Gas exchange, chemical composition and productive characteristics of tropical grasses deferred II: cultivars BRS Paiaguás and BRS Piatã

ABSTRACT This study aimed to evaluate the physiological parameters, the productive characteristics, structural and chemical composition of Urochloa Brizantha cultivars BRS and BRS Piatã submitted to two deferment periods and three using times. The experimental design was randomized complete block design in a factorial scheme 2 x 2 x 3, being two grass cultivars (Paiaguás grass and Piatã grass), two deferment periods (rainy season and dry-rainy transition) and three sealing times (40, 80 and 120 days). It was observed that, in the rainy season, the grasses had higher leaf transpiration rate when used for 40 days of deferment (1.66 µmol m2/s). During the rainy season, the Stomatal conductance was detected only in the grasses used with shorter seal, with an average of 0.07 µmol m2/s. In contrast, in the period of transition, the concentration decreased to 0.02 µmol m2/s. In a general way, the BRS Paiaguás presented lower content of NDF. The shorter cycle provided greater biomass production of total forage during the period of rain, approximately 2.78 times more than the same pasture grass deferred during the transition period. Generally, the periods of deferment and moments of use cause effects on structural characteristics of pasture, being that the period of deferment of the transition period and used for 40 and 80 days may be a strategy for keeping animals in critical periods.

摘要 本研究旨在评估经受两种休牧处理与三种利用时长的布里赞塔臂形草（Urochloa Brizantha）品种BRS与BRS Piatã的生理指标、生产性能、结构特性与化学组成。本实验采用2×2×3因子设计的随机完全区组设计，试验因子包括2个牧草品种（帕亚瓜斯草与皮亚塔草）、2个休牧期（雨季与雨旱过渡期）以及3个利用时长（40、80和120天）。研究观测到，在雨季条件下，休牧40天后进行利用的牧草叶片蒸腾速率更高，可达1.66 µmol·m⁻²·s⁻¹。在雨季，仅在休牧时长较短的牧草中可检测到气孔导度，平均值为0.07 µmol·m⁻²·s⁻¹。与之相反，在雨旱过渡期间，该指标数值降至0.02 µmol·m⁻²·s⁻¹。总体而言，BRS帕亚瓜斯的中性洗涤纤维（Neutral Detergent Fiber, NDF）含量更低。较短的休牧周期在雨季可使牧草总生物量产量更高，约为过渡期间休牧的同类牧草的2.78倍。总体而言，休牧期与利用时机对牧草结构特性存在显著影响，其中采用雨旱过渡期休牧并分别在休牧40天与80天时进行利用的方案，可作为牲畜关键饲养期的饲草保障策略。