Forage mass and canopy structure of Zuri and Quênia guineagrasses pasture under rotational stocking

ABSTRACT This work evaluated the productive and structural characteristics of the BRS Zuri and BRS Quênia cultivars under rotational stocking management. The evaluations were divided into five periods according to rainfall regime (high, medium, and low rainfall) during 16 months of the years 2016-2018. Pastures were grazed when canopies intercepted 95% of incident light to stubbles corresponding to 50% of the pre-grazing height. The pre- and post-grazing heights varied as a function of cultivar, with higher values for BRS Zuri (89 and 49 cm) than for BRS Quênia (78 and 45 cm). No differences in canopy lowering percentage, forage mass, and stem and dead material dry masses between cultivars were observed, with averages of 41.3%, 5,856, 1,835, and 841 kg ha−1, respectively. The post-grazing canopy height was lower in the second year, which resulted in higher values of canopy lowering percentage (51%). The highest value for leaf:stem ratio for both cultivars was observed in the high rainfall period of the second year. Higher average tiller population density was observed for BRS Quênia (477 tillers m−2) than for BRS Zuri (260 tillers m−2) for all the rainfall periods. Forage bulk density was similar between cultivars and varied according to the periods evaluated, with the highest value observed during the dry period of the year. Forage mass, as well as its component fractions, did not vary between cultivars, but was influenced by the studied periods. The cultivars showed high leaf mass in the pre-grazing forage mass with an average value of 3,174 kg ha−1. The cultivars are similar in morphological composition and offer high yield potential when managed under a rotational grazing system.

摘要 本研究评估了轮牧管理模式下BRS Zuri与BRS Quênia两个牧草品种的生产性能与结构特征。试验于2016-2018年的16个月周期内开展，依据降雨状况（高降雨、中降雨、低降雨）划分为五个试验阶段。当冠层截留95%的入射光照时，将牧草放牧至留茬高度为放牧前高度的50%，以此开展放牧处理。放牧前与放牧后高度因品种而异，BRS Zuri的对应值（89cm、49cm）高于BRS Quênia（78cm、45cm）。两品种在冠层高度降低率、牧草生物量、茎秆干物质质量及枯落物干物质质量方面均无显著差异，其平均值分别为41.3%、5856 kg·ha⁻¹、1835 kg·ha⁻¹与841 kg·ha⁻¹。第二年的放牧后冠层高度更低，使得冠层高度降低率达到51%的更高值。两个品种的叶茎比最高值均出现在第二年的高降雨阶段。在所有降雨阶段中，BRS Quênia的平均分蘖密度（477个·m⁻²）均高于BRS Zuri（260个·m⁻²）。两品种的牧草容重无显著差异，但随试验阶段发生变化，其最高值出现在年度干旱阶段。牧草生物量及其各组分分量在品种间无显著差异，但受试验阶段的显著影响。放牧前的牧草生物量中，两品种均拥有较高的叶片生物量，平均值为3174 kg·ha⁻¹。两个品种在形态组成上较为相似，在轮牧管理模式下具备较高的产量潜力。