Initial growth and survival of Eucalyptus spp. and Mimosa caesalpiniifolia Benth. in silvopastoral systems and their impact on herbage accumulation of Urochloa decumbens Stapf R. D. Webster

Silvopastoral systems (SPS) combine tree, herbaceous, and animal components, and may contribute to improve productivity and diversification of activities over time. This study evaluated the survival rate and dendrometry of seedlings of Eucalyptus spp. (eucalyptus) and Mimosa caesalpiniifolia Benth. (sabiá) and their impact on herbage responses of Urochloa decumbens Stapf R. D. Webster (signalgrass). The randomized complete blocks design in three replications (paddocks) was used. Treatments were: 1—monoculture of signalgrass; 2—signalgrass + eucalyptus (SPS—eucalyptus); 3—signalgrass + sabiá (SPS—sabiá); 4—monoculture of eucalyptus and, 5—monoculture of sabiá. The experiment was performed during 20 months in Pernambuco, Brazil. It was observed effect ( P = 0.0159) of treatments on the survival rates of the tree species, with the highest values obtained by the sabiá species (89.0 and 90.6% for SPS and monoculture respectively). There was effect of the interaction treatment × evaluation cycle ( P = 0.0004) on tree height, with the monoculture of sabiá reaching a height of 284 cm. Herbage accumulation and plant-part composition of signalgrass were similar in SPS and grass monoculture ( P > 0.05), however, it changed over sampling times (evaluation cycles), with the highest mean canopy height, total herbage mass and green herbage mass being observed at the beginning of the experimental period, and the lowest in the last evaluation cycle (71 and 21 cm; 10,342 and 218 kg DM ha −1 ; 2,985 and 152 kg DM ha −1 , respectively). The highest proportions of green fractions (leaf blade and stem) occurred in September and October 2019, coinciding with the end of the rainy season. Sabiá showed a faster initial growth when cultivated in monoculture and SPS when compared to eucalyptus, but both trees initial growth did not impact the herbage accumulation and plant-part composition of signalgrass.