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| Author(s): |
Gustavo Vinicios Munhoz Garcia
Total Authors: 1
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| Document type: | Master's Dissertation |
| Press: | Piracicaba. |
| Institution: | Universidade de São Paulo (USP). Centro de Energia Nuclear na Agricultura (CENA/STB) |
| Defense date: | 2022-10-14 |
| Examining board members: |
Valdemar Luiz Tornisielo;
Ana Carolina Dias Guimarães;
Rafael Munhoz Pedroso
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| Advisor: | Valdemar Luiz Tornisielo |
| Abstract | |
The straw present in tropical cropping systems contributes to weed control. At the same time, when associated with chemical control, it can result in reduced product efficacy. Pre-emergent herbicides such as diclosulam and diuron are applied directly to the soil or to the straw. When applied to the environment, these herbicides are subject to transport, retention, and degradation processes. Straw can be a barrier for the herbicide to reach the soil seed bank, reducing the efficacy of the product. And usually, this retention is attributed to a physical barrier, without considering the possible chemical interactions between straw and herbicide. Therefore, the objective of this work was to evaluate the influence of straw on the retention and mobility of 14C-diclosulam and 14C-diuron, as well as the mechanisms involved in this interaction. To evaluate these parameters, studies were conducted with radiometric, spectroscopic, and microscopic techniques on different types of straw (forage turnip - FT, buckwheat - BW, and black oat - BO). The retention of diuron and diclosulam is influenced by the type and amount of straw (p<0.05). High sorption rates of diclosulam (~28%) and diuron (~45%) were observed in BO straw. While lower amounts of diclosulam (~22%) and diuron (~33%) were sorbed in FT straw. Higher sorption and lower desorption were observed in the BO straw, with higher lipophilicity. At 2.5 t ha-1 about 81 - 100% of diclosulam and 76 - 93% of diuron were able to pass through the straw. With increasing the amount of straw (2.5 to 5 t ha-1) a reduction of 14 - 20% of diclosulam and 23 - 30% of diuron leaching occurs. Scanning electron microscopy analysis showed changes in the anatomical structures of the FT and BW straw after sorption, a result of the hydration process. While for AP, porous spaces are present increasing sorption and physical trapping of the molecules. Chemical changes were found in the straw-herbicide interaction, such as aliphatic amine bonds and haloalkanes (C-Cl and C-F). This chemical barrier results from the interaction between straw compounds (such as cellulose, hemicellulose, and lignin) with herbicide radicals. Thus, the retention process of pre-emergent herbicides in straw is characterized as physical and chemical, influenced by chemical, physical and anatomical aspects of the straw. Evidencing the mechanisms of interaction between herbicides and organic materials in reducing the availability of these molecules in the environment. Organic materials such as straw can act to reduce the environmental risk of herbicides. But it can also reduce the control efficacy of the herbicide against the soil seed bank (AU) | |
| FAPESP's process: | 20/12644-3 - Pre-emergent herbicides behavior in straw of different cover crops |
| Grantee: | Gustavo Vinícios Munhoz Garcia |
| Support Opportunities: | Scholarships in Brazil - Master |