Fluxo de biomassa e estrutura do dossel em híbridos de sorgo manejados sob frequências de pastejo com ovinos

Abstract

In arid and semi-arid regions, the poor distribution of rainfall causes great variation in the quantity and quality of forage produced. The use of semi-perennial grasses, such as sorghum, for grazing may prolong the period of forage supply in the field. This study evaluated two sorghum hybrids under two grazing frequencies (60 and 80 cm canopy height), managed under intermittent stocking with sheep. The experiment was conducted at Núcleo de Ensino e Estudos em Forragicultura - NEEF/DZ/CCA/UF, Fortaleza - CE. The treatments consisted of combinations between two hybrids of Sorghum bicolor and S. sudanense (BR007A x TX2785 and CMSXS157A x TX2785, named hybrids BR and CM, respectively) and two grazing frequencies (60 and 80 cm canopy height), in a 2x2 factorial randomized block design, with four replications, totaling 16 experimental units of 100 m². Defoliation was carried out by Morada Nova sheep, managed under intermittent stocking using the mob-stocking technique. There was a longer resting period in the first regrowth cycle in relation to cycles 2 and 3 in all adopted managements. The LER1/LER2 ratio was superior in pastures under CMx80 combination in comparison to the other treatments. Pastures of CM hybrid at both frequencies presented higher leaf elongation rate. Values of stem elongation rate and the phyllochron were higher in the BR hybrid pastures at the 80 cm frequency. The leaf life span was superior in the BR hybrid pastures at the 60 cm frequency. The CMx80 combination showed higher anterior leaf senescence rate. The posterior leaf senescence rate was higher in the CM hybrid pastures at the 80 cm frequency. The CMx60 combination showed lower total forage accumulation rate. Higher green forage accumulation rate was found in the BRx60 and CMx80 combinations. Higher leaf area index was observed in BR hybrid pastures. The CMx60 combination presented higher photosynthetically active radiation interception and grazing horizon than the other treatments. The BR hybrid presented higher tiller population density in the two grazing frequencies. The number of new leaves per tiller and the leaf blade length were greater in the CMx80 combination. Higher mean values of total forage biomass, green forage biomass and green stem biomass were verified in BR hybrid pastures in the 80 cm frequency. The green leaf biomass revealed lower value in the pastures under CMx60 combination. The pastures managed with 60 cm presented higher dead forage biomass. The leaf/stem ratio revealed lower values in BR hybrid grasses in both frequencies. The CM hybrid managed with 60 cm height is the best management option, showing good accessibility of the animals to this grazing horizon and less difficulty in harvesting this forage by grazing sheep