Características estruturais e morfológicas relacionadas à eficiência de pastejo em Pennisetum sp. no período de seca

Abstract

The experiment was carried out at the IPA Experimental Station, Itambé-PE, located in the Forest Zone of Pernambuco. The objective was study structural and morphologic characteristics and evaluate factors related the grazing efficiency in five Pennisetum sp. genotypes (IRI-381, Venezuela, HV-241, Elephant B and Hexaploid) during the dry period of the year. Genotypes were managed under rotational stocking (44 days of resting period and four days of grazing period). The experimental design was complete randomized blocks in split plot (genotypes represented the plots; grazing cycles, the subplots) and four replications. Six replications were used for total, green and dry pre-grazing leaf blade mass. The others variables (green leaf blade accumulation and grazing efficiency) were analyzed using a complete randomizedblocks design with four repetitions. There was variation in the structural and morphologic characteristics of the Pennisetum sp. genotypes. The IRI-381 and Elephant B presented high density of green leaf blade, low percentage of dead material and high density of remaining basal tillers and new aerial tillers, with averages of 5.0 kg DM/ha/cm, 33%, 22 and 146 tillers/m2, respectively. The same genotypes presented greater total and green pre-grazing leaf blade mass, and green leaf blade accumulation and grazing efficiency, with averages of 1374 and 737 kg DM/ha, 654 kg DM/ha/44 days and 80% of the green leaf blade accumulation, respectively. The HV-241 presented high participation of died material in its aerial biomass (55.6%) due to the high tiller mortality (19 and 114 basal and aerial dead tillers/m2, respectively). This genotype stillpresented high grazing efficiency (100% of the green leaf blade accumulation), however low green leaf blade accumulation (155 kg of MS/ha/44 days). Lesser grazing efficiencies were observed in the Hexaploid and Venezuela (59 and 36% of the green leaf blade accumulation, respectively), possibly due to the high losses by grazing (30 and 31% of the pre-grazing total leaf blade mass, respectively). The alterations in the structural and morphologic characteristics of the Pennisetum sp. genotypes suggest that the animal stoking will have to be adjusted to each grazing cycle aiming at the maintenance of forage stand and the quality of the animal diet. The genotypes IRI-381 and Elephant B presented potential to be used under rotational stocking in dry period of the year. There were indications that interspecific hybrid HV-241 was more affected bythe effect of the dry period of the year.