Produção de biomassa e composição químico-bromatológica de Desmanthus pernambucanus (L.) Thellung submetida a crescentes níveis salinos

Abstract

The adoption of forage species adapted to saline conditions can optimize the use of salinized soils. The Desmanthus pernambucanus (L.) Thellung, known as Jureminha and adapted to the climatic conditions of the semiarid Brazilian regions, presents high acceptability by part the animals. The objective was to characterize the biomass production of the aerial part and to determine the chemical-bromatological composition of Jureminha plants submitted to increasing salt levels. The experiment was conducted in a greenhouse, in a completely randomized design, with five treatments (0, 25, 50, 75 and 100 mM NaCl) and six replicates. Fifty-eight days after transplanting, the uniformization cut was performed (intensity of 20 cm, with only the main stem remaining). Then the treatments were applied, and every 54 days cuts were made, being the vegetal material collected separated in the fractions: stem, leaf and pod. In October and November, mortality was observed of 83 and 100% of the plants submitted to 100 mM NaCl, respectively, being that and only 50% of the plants submitted to 75 mM survived until November. In august, it was verified, through the number of pods, that the plants were in the stage of filling of grains, being in this cutting cycle verified the following changes: increase of biomass production of pods (148%); leaf/stem ratio reduction (33%); reduction in crude protein contents (16 and 14% for leaves and stems, respectively); increase in fibrous compounds (NDF: 11 and 9%, on average, for leaves and stems, respectively); decrease in soluble carbohydrate contents (28 and 17%, on average, for leaves and stems, respectively) and increase of proline in the stems (62%). No effect of salinity was observed on proline content in leaves and stems. As for the chemical composition, it was observed in both leaves and stems that the harmful effects of salinity were potentialited by the grains filling phase, with an increase in Na+ concentrations (253 and 217%, on average, from June to October in leaves and stems, respectively, and from 321 and 427%, on average, from 0 mM to 100 mM in August), and K+ reduction (26 and 29%, on average, for leaves and stems, respectively). It is concluded that salinity negatively affects the production and chemical-bromatological composition of forage of Jureminha, which tolerated, without great damages, salinities close to 50 mM. Cut management and plant phenological phase potentialized the effects of salinity.