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.
Highlights
Paclobutrazol (PBZ), a derivative of the triazole group, is commercially used in many tropical and subtropical fruit crops for regulation of growth, flowering and yield and commonly (Srivastav et al, 2010) used in mango cultivation in the semi-arid northeastern Brazil
Mathematical models are available for various agricultural purposes, among which is the simulation of absorption of organic substances by plants (Fujisawa et al, 2002), as well as the behavior of organic substances in the soil (Gang et al, 2003; Milfont et al, 2008)
An average of 1.5 kg of soil at a depth of 15 and 30 cm was collected from four points around eight plants. These samples were stored in a refrigerator until the beginning of the biodegradation tests
Summary
Paclobutrazol (PBZ), a derivative of the triazole group, is commercially used in many tropical and subtropical fruit crops for regulation of growth, flowering and yield and commonly (Srivastav et al, 2010) used in mango cultivation in the semi-arid northeastern Brazil. For many complex compounds, kinetics first order is not appropriate because the biodegradation of these compounds can occur at different rates throughout the process In this case, the kinetic model results, using double first-order, have shown to work well, especially when the biodegradation occurs primarily in a fast reaction and decays at a slow rate (López-Galindo et al, 2010). Vaz et al (2012) made a study of PBZ biodegradation in saturated soil without the addition of microorganisms (or only with the participation of microorganisms naturally present in the ground). These authors achieved further adjustments in modeling of PBZ biodegradation using double first-order kinetics. Analysis of variance was performed using Microcal Origin 6.0 (Table 1)
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