Resumen de Coupling pesticides fate modelling and conservation cropping systems to reduce the agriculture footprints on ecosystems
Conventional agriculture is an intensive farming practice that involves the use of excessive soil tillage, intensive land use, continuous inputs of synthetic chemical fertilizers and pesticides, heavy irrigation, and concentrated monoculture production. This type of agriculture is widely used as it has been successful in increasing food production and meeting the demands of a growing global population. However, it has also been associated with several environmental and sustainability issues, including soil degradation, erosion and runoff, loss of microbial diversity, chemical pollution, groundwater contamination, and emission of greenhouse gases. In response to these challenges, new soil management practices and cropping systems have been developed and implemented in the last decades to ensure alternative and more sustainable farming systems. These new practices address some of these issues while promoting long-term sustainable and environmentally friendly agricultural practices. These new approaches are represented by conservation agriculture.
These practices include non-tillage, the presence of cover crops during the fallow period, and the accumulation of harvested crop residues as mulch on the soil surface (mulching). Non-tillage and the presence of crop residues on the soil surface improve soil structure, fertility, and organic matter content, protect the soil from wind and water erosion, and maintain soil moisture while reducing the need for irrigation and increase soil microbial biodiversity.
Accordingly, all these agricultural practices and soil management have important social and agricultural benefits. However, the use of pesticides remains, to a greater or lesser extent, necessary even in this type of conservation agriculture from a productive point of view. Farmers consider pesticides (mainly herbicides) essential chemicals for increasing crop yields by controlling pests and diseases that threaten the food supply. In this regard, it is necessary to take into account that the application of these conservation management practices results in changes in soil physicochemical properties, which could modify the processes that govern the dynamics of herbicides in natural soils (adsorption, desorption, degradation/dissipation, mobility via leaching or runoff, and volatilization). Changes in these processes are highly relevant to predict the current and future environmental fate of herbicides in soils under conservation agricultural practices. Therefore, the knowledge of the fate of applied herbicides under conservation practices is particularly important and needs to be carefully studied in order to assess and minimize their potential environmental risk to soil and water quality. In this sense, the use of mathematical models, which evaluate the environmental fate of these compounds is of great interest, especially if they are parameterized and tested with data and results obtained under field conditions. These models, after a correct validation, can be used as a tool to predict pesticide concentrations in the different environmental compartments (soil, air, plant and water) in the long-term without carrying out further experimental tests.
In accordance with the above, and considering that there is only a few studies that combine intermediate cover crops, mulching and pesticide fate models, the main objective of this thesis was to study under real field conditions (experimental plots) the effect of conservation agricultural practices including intermediate cover crops, the accumulation of crop residues on the soil surface (mulching), non-tillage, and direct seeding, on the environmental fate of three herbicides, S-metolachlor (SMOC), foramsulfuron (FORAM) and thiencarbazone-methyl (TCM). The study was carried out through: 1) the evaluation of the dissipation, persistence, distribution and/or mobility of the herbicides in the soil profiles under conventional and conservation cropping systems, 2) the changes in soil microbial communities influenced by these agronomic practices as indicators of soil quality and conservation, and 3) the modelling of the herbicides environmental fate using PRZM (Pesticide Root Zone Model) and MACRO (Water and solute transport in macroporous soils) models, that were parameterised and validated with data measured under real field conditions to predict the impact and viability of these agronomic practices on soil sustainability and surface and groundwater quality in the long-term.
