Abstract

Paclobutrazol (PBZ) is a plant growth regulator, increasing flowe ring and yield that is widely used in mango cultivation in the semi-arid northeastern Brazil. PBZ remains active in the soil for several years. However, it can severely affect the growth and development of subsequent crops, mainly by reducing vegetative vigor. The aim of this study was to investigate PBZ biodegradation in four samples of soil: P-G (with PBZ application history and with addition of glycerol); NP-G (without PBZ application history and with addition of glycerol); P-NG (with PBZ application history and without addition of glycerol) and NP-NG (without PBZ application history and without addition of glycerol). The biodegradation experiments were carried out in 125 ml flasks containing 10 g soil, at room temperature for 63 days. Mathematical models to analyze the kinetics of degradation of PBZ were applied. PBZ residue was less than 1% in soils with a history, regardless the addition of glycerol. The three models (first-order kinetics, double first-order kinetics and logistic) were well adjusted in these cases (P-G and P-NG). On the other hand, PBZ biodegradation in soil NP-G and NP-NG was 64%, and followed the model of double kinetic. PBZ biodegradation in soil with history was successful, probably because the native microbial had adapted to local environmental conditions.

Key words: Paclobutrazol, biodegradation, mathematical models.