Organic matter and herbicides sorption in soils under no-tillage in tropical and subtropical regions of Brazil

Author(s)

Eloana Janice Bonfleur

• Document type: Doctoral Thesis
• Press: Piracicaba.
• Institution: Universidade de São Paulo (USP). Escola Superior de Agricultura Luiz de Queiroz (ESALA/BC)
• Defense date: 2014-06-27

Examining board members

Jussara Borges Regitano; Antonio Carlos de Azevedo; Robson Rólland Monticelli Barizon; Deborah Pinheiro Dick; Pablo Vidal Torrado

• Advisor: Jussara Borges Regitano

Abstract

No-tillage System (NT) is widely used in Brazil due to improve soil quality and reduce production costs compared to conventional tillage. Different climatic conditions and the adoption of different cultures in the offseason suggest differences in the distribution and quality of soil organic matter (SOM) due to the resilience time of straw in coverage in NT. Interactions between SOM and pesticides has been widely studied, but only partially elucidated. In most of studies, the MOS as a homogeneous compartment and there is not the knowledge about the role of its various molecular components. Therefore, the aim of this work is to evaluate the effect of the composition, distribution and interaction with the mineral phase of SOM on sorption of herbicides applied to soybean and corn under no-tillage in tropical (Central-west) and subtropical (South Region) soils. Alachlor, bentazon and imazethapyr herbicides were selected because of its large use in these cultures and different physicochemical properties. For this, it was sampled 12 soils at 0-5 cm layer excluding the straw surface, six representing the Paraná State (subtropical) and six representative of Mato Grosso de Sul State (tropical). Physical and chemical attributes, iron and aluminum forms, study of quality of SOM by Nuclear Magnetic Resonance Spectroscopy of 13C and soil physical fractionation methods were used for this purpose. Greater accumulation of organic carbon (OC) was observed in subtropical soils due to higher low crystalline aluminum oxides contents, in addition to lower temperatures and higher moisture in this region. For soils of both regions, the SOM stabilization occurs through the formation of complexes in the clay fraction (~ 50 % of the OC content). Regarding interactions with the mineral phase, it was observed that aluminum oxides are related to physical protection of SOM while iron oxides appear to participate in the decomposition and humification reactions by forming complexes with carboxylic groups. For alachlor, low crystallinity aluminum forms decreased its MOS sorption but sorption of this herbicide was not correlated with any functional group. For bentazon, positive correlation was observed between sorption and more decomposed organic material and with the complexed aluminum in MOS. For imazethapyr, there were positive correlations with iron and aluminum forms and carboxyl functional group. For the three herbicides better sorption was observed in the silt size fractions (53-2 ?m) and in general, sorption in tropical was higher than in subtropical soils. The effect of charge sites exposure after soil physical fractionation was evident for imazethapyr increasing its sorption compared to the whole soil which shows the greatest amount of blocked sites in tropical soils. (AU)

• FAPESP's process: 10/19396-3 - Organic matter and sorption of herbicides in no-till soils of tropical and subtropical regions of Brazil
• Grantee: Eloana Janice Bonfleur
• Support Opportunities: Scholarships in Brazil - Doctorate