Omissão de nutrientes, adubação com boro e carga de frutos em oliveiras: influência nos parâmetros morfométricos, fisiológicos e de qualidade do azeite

Abstract

Oliviculture in Brazil has been expanding in recent decades, however for the activity to prosper, research on management is essential, with emphasis on the area of fertility and fertilization. Another important aspect in olive growing refers to the biannuality and heterogeneous production in olive groves, highlighting the relevance of studies about trees with different fruit loads. Thus, the aim of this Thesis was to investigate the nutritional status of olive trees (Olea europaea L. cultivar Arbequina) under conditions of deficiency and fertilization and the relationship between fruit load and oil physical-chemical quality. Thus, three independent studies were carried out, the first of which evaluated nutritional deficiency in young olive trees under nutrient omission for three years in a greenhouse, in the municipality of São Gabriel (RS); the second addressed the effect of boron (B) fertilization on adult olive trees in São Gabriel and Caçapava do Sul (RS); the third focused on the relationship between fruit load and oil quality, as well as the comparison between two olive groves in Caçapava do Sul in terms of fruit and oil parameters. The omission of nitrogen (N), phosphorus (P), potassium (K) and B altered at least one of the morphometric parameters analyzed, as well as the content of nutrients and phenolic compounds. Olive trees deprived of N exhibited high nutritional stress, with smaller stem diameter and dry matter in the branches, as well as higher levels of phenolic compounds in the leaves and the opposite trend in the roots. The omission of P produced late symptoms, with an increase in most phenolic compounds, especially oleuropein and verbascoside. The deprivation of B and K induced more attenuated symptoms, even with the -K treatment showing greater root length and density than the complete treatment. In study 2, it was verified that soil and foliar fertilization with B did not alter the B content in the leaves and only kaempferol showed a higher concentration in the treatment with 100 g ulexite/with foliar. However, lower levels of B were observed at flowering, regardless of treatment, suggesting mobilization of nutrients from leaves to attend flowering demand. Concerning study 3, no significant differences were observed between fruit loads on the lipid content of the fruits, as well as in most of the quality parameters. However, trees with low production showed a higher concentration of oleuropein and verbascoside in the fruits, in addition to oleacein and oleocanthal in the oil. A greater amount of P content was also observed in low fruit load and of B in high fruit load. The extraction and quality of the oil differed between the olive groves, with higher yield and extractability of olive oil in the olive grove harvested with more mature fruits, in addition the quality parameters were within the norms, showing a higher content of oleic acid, oleacein and hydroxytyrosol in the olive oil. Thus, fruits with a maturation index close to 4 led to greater oil production, without impairing product quality.