MORFOLOGIC CHARACTERIZATION ON MARANDU GRASS PASTURES SUBMITTED TO DEFOLIATION FREQUENCIES AND FERTILIZATION LEVELS

Abstract Tillers are the basic units of growth in forage grasses and tillering is responsible for the adaptation and reestablishment of grass after defoliation. Therefore, it is important to understand the morphological changes of tillers due to defoliation environment and fertilization, which are two important pasture management strategies. In this study, we aimed to characterize the morfologic response of marandu grass tillers before nitrogen fertilization and frequency of defoliation for a better understanding of the phenotypic plasticity of this plant. This study was carried out in two experimental years. The treatments in the first year consisted of different cutting intervals (7, 14, 28, 56, and 112 days). In the second year, besides the same cutting intervals, two fertilization conditions were studied: a low level (21.5 kg.ha-1 P and 75 kg.ha-1 N) and a high level (43 kg.ha-1 P and 300 kg.ha-1 N). A randomized block design was adopted and in experiment two a factorial scheme with four repetitions was used. In both experiments the responses to stem length, leaf blade length, space between leaf blade and leaf area, and weight of tiller increased with cutting intervals. In experiment two, high doses of fertilization provided larger number of vegetative tillers, space between leaf blades, tiller weight, longer leaves and stems, and higher population densities of reproductive tillers with longer cutting intervals. In conclusion, the defoliation and the nitrogen and phosphorous fertilization produced morphologic modifications in marandu grass tillers suggesting the phenotypic plasticity of this grass.

摘要 分蘖（tillers）是禾本科牧草生长的基本单元，分蘖能力决定了牧草在被刈割后的适应性与种群重建能力。因此，探究刈割环境与施肥这两种核心牧场管理策略下，分蘖的形态变化具有重要学术价值。本研究旨在解析马兰杜草（marandu grass）分蘖在施氮与刈割频率下的形态响应，以深入理解该植物的表型可塑性。本试验于两个年度开展：第一年的处理设置为不同刈割间隔（7、14、28、56及112天）；第二年除保留相同的刈割间隔梯度外，额外设置两种施肥水平：低肥组（21.5 kg·ha⁻¹ 磷（P）与75 kg·ha⁻¹ 氮（N））及高肥组（43 kg·ha⁻¹ 磷（P）与300 kg·ha⁻¹ 氮（N））。两项试验均采用随机区组设计，第二年试验采用四重复析因方案。在两项试验中，随刈割间隔延长，茎秆长度、叶片长度、叶间距与叶面积、分蘖重量均显著提升。第二年试验结果显示，高剂量施肥可显著增加营养分蘖数量、叶间距、分蘖重量、叶片与茎秆长度，且在更长刈割间隔下，生殖分蘖的种群密度更高。综上，刈割以及氮、磷施肥均可诱导马兰杜草分蘖产生形态学改变，表明该牧草具备表型可塑性。