Full text
| |
| Author(s): |
Wadson Sebastião Duarte da Rocha
Total Authors: 1
|
| Document type: | Doctoral Thesis |
| Press: | Piracicaba. |
| Institution: | Universidade de São Paulo (USP). Escola Superior de Agricultura Luiz de Queiroz (ESALA/BC) |
| Defense date: | 2003-08-11 |
| Examining board members: |
Luis Reynaldo Ferracciu Alleoni;
Arquimedes Lavorenti;
Luiz Carlos Luchini;
Valdemar Luiz Tornisielo
|
| Advisor: | Luis Reynaldo Ferracciu Alleoni |
| Abstract | |
The dynamic of herbicides in soils is influenced by soil moisture and organic matter contents and also by their quality, which are variable in the organic-mineral aggregates of the soils. The aims of this research were to evaluate the effects of soil moisture on the mineralization and sorption of the herbicides 2,4-D (weak acid) and diuron (non-ionic), in four Oxisols with different contents of soil organic matter (SOM), as well as to evaluate the influence of aggregate sizes (> 150, 54 - 150, 21 - 53, 2 - 20 and < 2 mm) and degree of humification in the sorption of these herbicides. Surface samples (0 - 0.2 m) of one Xanthic Hapludox (LAd, from Piracicaba/SP), one Xanthic Acrudox (LAw, from Uberlândia/MG), and two Anionic Acrudox (LVw-1 from Uberlândia/MG and LVw-2 from Canoinhas/SC) were collected. SOM, phosphorus, K + , Ca 2+ , and Mg 2+ contents and pH values (in H2 O, in KCl 1.0 mol L -1 and in CaCl2 0.01 mol L -1 ) were measured, whereas H+Al was calculated. Fe, Al, and Si oxides were quantified after soil extraction with H2SO4. Free and amorphous Fe oxides were determined by DCB and oxalate method, respectively. Granulometric analysis and water dispersed clay (WDC) were quantified by the densimeter method. The mineralogy was evaluated by X-ray diffraction. In order to quantify soil organic-mineral aggregates, 40 g of soil was added to 160 mL of distilled water in centrifuge tubes, which were shaken for 16 h at 160 rpm and sonicated for 15 min at 240 W. The aggregates > 150 and 53 - 150 mm were obtained by sieving, whereas the aggregates < 53 mm were obtained by sedimentation. Soil and aggregate organic carbon contents were obtained by combustion. The soil microbial activity was obtained by the radiorespirometry method. Soils were incubated with 14 C-2,4-D and 14 C-diuron, for 42 d at 25, 50 and 75 % of the field capacity and remained in a semi-dark room at controlled temperature of 22 ± 2 o C. Then, the pesticides were extracted three times with CaCl2 0.01 mol L -1 and, afterwards, the soil samples were fractionated in order to quantify the amount of herbicides in the aggregates. In these, the degree of humification was obtained by fluorescence. Diffusion markedly affected the herbicides sorption. For example, 2,4-D mineralization was 62 % on LAd only at 75 % field capacity. As expected, 2,4-D was less sorbed on LAd that had higher pH and lower SOM content. In general, the soils presented higher amounts of aggregates > 150 mm. The organic-mineral aggregates < 53 mm presented higher organic carbon content. However, the herbicides were more sorbed in the aggregates > 53 mm, except for LAd. When the soil were at 75 % of the field capacity, the sorption increased in the aggregates < 53 mm for 2,4-D, but it was only verified for LAw and LVw-1 for diuron. The successive extractions altered the aggregate stability. The LAd located in a tilled area had higher degree of humification than the LVw-2 located in a non-tilled area. The soil aggregates between 53 and 150 mm presented higher degree of humification. (AU) | |