MORPHOGENETIC AND STRUCTURAL CHARACTERISTICS OF ALEXANDERGRASS PASTURES UNDER CONTINUOUS STOCKING

Abstract The aim of this study was to evaluate some morphogenetic and structural characteristics to explain variations in forage accumulation of Alexandergrass (Urochloa (Syn. Brachiaria) plantaginea) under continuous stocking method. The experimental treatments consisted of four grazing heights (10, 20, 30, and 40 cm), allocated to experimental units following a randomized block design with three replicates. The following variables were analyzed: leaf appearance, elongation, and senescence rates, leaf lamina length, number of leaves per tiller, leaf area index (LAI), and forage accumulation rate. Data were submitted to analysis of variance and means were compared by Student's t-test (P≤0.05). The main results were: i) different grazing heights had different tissue flows; ii) grazing heights between 30-40 cm showed the highest LAI, and produced similar values; iii) forage accumulation rate increased according to grazing height increments, but did not change above 30 cm. In conclusion, Alexandergrass pastures under continuous stocking should not be maintained at grazing heights lower than 30 cm if the objective is to maximize forage production.摘要 本研究旨在评估多项形态发生与结构特征，以阐明连续放牧法下亚历山大草（Alexandergrass，学名Urochloa (Syn. Brachiaria) plantaginea）的牧草累积量变异规律。试验设置4个放牧高度梯度（10、20、30与40 cm），采用随机区组设计将处理分配至试验单元，设置3次生物学重复。本研究分析的观测指标包括：叶片出叶速率、伸长速率与衰老速率，单叶叶片长度、单分蘖叶片数、叶面积指数（leaf area index, LAI）以及牧草累积速率。数据经方差分析后，采用t检验（Student's t-test）进行组间均值比较，显著性水平设定为P≤0.05。主要研究结果如下：① 不同放牧高度下的组织周转模式存在显著差异；② 30~40 cm放牧高度区间的叶面积指数最高，且组间测定值无显著差异；③ 牧草累积速率随放牧高度升高呈上升趋势，但当放牧高度超过30 cm后，该速率不再发生显著变化。综上，若以最大化牧草产量为目标，采用连续放牧法管理的亚历山大草草地，其放牧高度不应低于30 cm。