Growth indexes of Pennisetum purpureum cv. Roxo cultivated in different seasons under rainfed conditions

ABSTRACT The objective was to estimate the growth indexes of elephant grass cv. Roxo managed under rainfed conditions in different growing seasons. Seven growth ages (9, 18, 27, 36, 45, 54, and 63 days) were evaluated in three growing seasons (rainy, transition and dry). A completely randomised design was adopted, with split-plot arrangement with time repeated measures, with the ages being the plots and the seasons the subplots. Interaction of age x season was observed. The specific leaf area mean was 0.0286 ± 0.0039 during the rainy season. In the transition season, it adjusted to a third-degree polynomial model; in the dry season it declined linearly (0.0003 m2 g-1). The leaf weight ratio adjusted to the third-degree polynomial model in the rainy and dry seasons, and in the transition season it was maximised at 28 DAC (0.694 g g-1). The leaf area ratio continuously declined in the rainy season. In the transition and dry seasons, it adjusted to the third-degree polynomial model. The net assimilation rate presented averages of 3.73 ± 2.50 and 3.63 ± 1.48 g m-2 day-1 in the rainy and transition seasons, respectively. In the dry season, it was minimised at 48.4 days. The relative growth rate mean was 0.0075 ± 0.0037 during the rainy season. In the transition and dry seasons, it adjusted to the third-degree polynomial model. The growth index rates of elephant grass cv. Roxo are modified by growing seasons, and the pattern and magnitude of the response varies throughout the growth cycle.

摘要 本研究旨在估算不同生育季雨养栽培模式下管理的罗索象草（elephant grass cv. Roxo）的生长指标。试验在3个生育季（雨季、过渡期与旱季）中，对7个生育龄期（9、18、27、36、45、54及63天）的植株进行了评价。试验采用完全随机设计，设置裂区排列并开展时间重复测量，其中生育龄期为主区，生育季为副区。观测到生育龄期与生育季存在交互效应。雨季的比叶面积（specific leaf area）均值为0.0286 ± 0.0039。过渡期的比叶面积拟合为三次多项式模型；旱季的比叶面积呈线性下降趋势，下降速率为0.0003 m²·g⁻¹。叶重量比（leaf weight ratio）在雨季与旱季均拟合为三次多项式模型；过渡期的叶重量比在28 DAC时达到最大值，为0.694 g·g⁻¹。叶面积比（leaf area ratio）在雨季呈持续下降趋势；过渡期与旱季的叶面积比则拟合为三次多项式模型。净同化率（net assimilation rate）在雨季与过渡期的均值分别为3.73 ± 2.50 g·m⁻²·d⁻¹与3.63 ± 1.48 g·m⁻²·d⁻¹。旱季的净同化率在48.4天时达到最小值。雨季的相对生长率（relative growth rate）均值为0.0075 ± 0.0037。过渡期与旱季的相对生长率均拟合为三次多项式模型。罗索象草的生长指标速率受生育季调控，其响应模式与响应幅度在整个生育周期中呈动态变化。