Fracionamento de boro em solos de plantio de Oliveiras (olea europaea l.) no Sul do Brasil

Abstract

Boron is an essential micronutrient for plant development, so it is essential to understand how B behaves in the soil to indicate a fertilizer recommendation. In soils of RS state limed to neutral pH, as those cropped with olive orchards, there are gaps about the ways in which B fertilizers affect B fractions in the soil and about the effectiveness of standard procedure for evaluating available B. This study aimed to quantify B fractions in limed soils from olive orchards of RS state, their relationships with available B from three extraction methods, and their relations with soil attributes. Samples from five soils were taken and incubated for 30 days, unamended and amended with ulexite and boric acid. To assess the B content, the hot water extraction method was compared with two more methods used internationally for this purpose, with 0.01 M CaCl2 + 0.05 M mannitol (CARTWRIGHT et al., 1983) and HCl 0,05 M. Sequential fractionation was performed according to the method adapted from Datta et al. (2002), using extractors specific to each form or fraction. The hot water method showed a significant correlation with the other two extraction methods, although the two alternative methods had larger B values than B-hot water. B fractionation in non-amended soils pointed the largest B fraction is that linked to organic matter (41.5%), while 23% is readily soluble. Ammendment of both B fertilizers increased labile B forms in detriment of a decrease in relative content of more recalcitrant fractions. The percentage of labile fractions is inversely proportional to the clay and oxides contents in the soils, while organic matter contents seemed to have smaller effect than texture and mineralogy. The fractionation scheme proved to be satisfactory and useful in monitoring the distribution and dynamics of fractions B in soils, but some there are some limitation/difficulties for estimation of recalcitrant fractions of B in the evaluated soils.