Respostas morfofisiológicas e produtivas de genótipos de Pennisetum purpureum Schum. de porte baixo sob lotação intermitente de ovinos na Zona da Mata de Pernambuco

Abstract

The research was conducted at the Experimental Station of the Agronomic Institute of Pernambuco (IPA) located in Itambé, dry rainforest region of Pernambuco. The objective was to estimate the coefficients of repeatability, of determination (R2) and the number of measures needed to predict the real value [using principal component analysis (PCA)] to variable morphophysiological and productive, and the responses dwarf elephant grass pasture under grazing sheep. The experiment was carried out in a randomized block design with five Pennisetum purpureum clones were evaluated: Taiwan A-146 2.27, Taiwan A-146 2.37, Taiwan A-146 2114, Merker Mexico MX 6.31 and Mott. Evaluations were performed during five grazing cycles, from September 2008 to April 2009. Twenty five sheep (42 kg average liveweight) were used in a mobgrazing protocol, leaving the paddock at 30 cm of residual stubble height. The clones were managed under rotational stocking, with 32 days of resting period and three days of grazing period for cycles 1, 2, and 5, and 64 days of resting period and two days ofgrazing period for cycles 3 and 4. Response variables analyzed at pre- and post-grazing included leaf area index, light interception, leaf angle, average sward height, green portion of herbage mass (DM basis). In addition, we estimated net herbage accumulation (ALF), in kg DM ha-1 cycle-1, and net herbage accumulation rate (TALF), in kg DM ha-1 day-1. Data were analyzed by univariate or multivariate analysis of repeated measures over time in the SAS. Means were compared by Tukey test at 5% probability. According to the PCA, for the variables LAI and LI in cycles of shorter period of regrowth, and height of plants in the cycles of higher period of rest is needed only one measurement (R2=0.80), classifying them among the characteristics evaluatedas the easiest prediction in elephant grass clones. Assessments for NHA and NHAR size of dwarf elephant grass, under grazing, need long experimental periods.