Análise de trilha e caracterização de clones de Pennisetum sob corte, na Zona da Mata seca de Pernambuco

Abstract

The experiment was carried out at the IPA Experimental Station, Itambé-PE. The objectiv was to evaluate the direct and indirect relationship between the explanatory variables and the total dry matter yield and the leaf blade dry matter yield using a trail analysis approach. In addition to that, it was evaluated the nutritive value and dry matter production of five Pennisetum clones (IRI-381, HV 241, Venezuela, Elefante B and Hexaplóide) under cut, in the Forest Zone of Pernambuco. The experiment was accomplished in an exclusion area located in a grazed plot, divided in 6 paddocks. The paddocks were subdivided in five areas of approximately 833 m2. Each subdivision was occupied by a genotype of Pennisetum, and the exclusion area of each subdivision corresponded to 24 m2 (4 x 6 m). The design was complete randomized blocks, with six replications. The experimental period begun with a staging cut at ground level (17/08/2005) followed by evaluation cuts every 60 days thereafter. The evaluations were accomplished inside a square of 1 m2, within an utile area of 2 m2. For the study of the effect of the variables in the trail analysis, it was considered as main dependent variables the total dry matter production (PMST) and leaf blade dry matterproduction (PMSLF), in t/ha. As explanatory independent variables, the following variables were used: average plant height (AP), number of sheets/tiller (NFP), number of basal tillers/m2 (NP), tiller mass, in kg (PP), stem diameter (DC) and relationship leaf blade/stem(RFC). The stem diameter did not present significant correlations with total dry matter yield and leaf blade dry matter yield; therefore, it was withdrawn from the trail analysis study. The following response variables were determined: dry matter concentration (DM), crude protein (CP), neutral detergent fiber (NDF), acid detergent fiber (ADF), ether extract (EE), mineral matter (MM), in vitro dry matter digestibility (IVDMD), total carbohydrates (TC),and non-fibrous carbohydrates (NFC). Just the ADF and TC concentrations in the leaf blade differed among the evaluated clones. The other parameters presented medium heritability,inferring genetic variability. The variables presented positive correlations of medium to highmagnitude; however, the number of basal tillers and the relationship leaf blade/stem presented negative Pearson correlation with all the other variables, except between themselves. The stem diameter did not present significant correlation with the productive variables, being excluded of the trail analysis. The plant height presented high correlation with the production of total dry matter (0,911), however, the increase in the total dry matter yield was better explained by the stem mass. Regarding the leaf blade dry matter yield, the leaf blade mass presented the highest correlation with that dependent variable (0,711), but the number of leaf blade/tiller explained better the increase on the leaf blade dry matter yield. The leaf blade and stem dry matter yields didn't present significant differences, with productivity of 1.7 t of DM/ha and 2.1 t of DM/ha, respectively. The leaf blade nutritive value presented significant and high heritability for ADF and TC, indicating that there were genetic differences among the appraised clones. This fact did not happen with the stem nutritive value which did not show significant differences among treatments for the evaluated response variables, presenting medium to high heritability. Considering these results, we concluded that the stem mass presented nutritive value similar to the leaf blade,indicating that for these clones, it is possible the use at 60 days of regrowth. The stem mass and the number of leaf blade/tiller explained better the increase on the dry matter production.