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Pesticide dynamics within mulches in a context of conservation agriculture: towards a coupled modelling tool

Study of the interactions between pesticides and mulches in conservation agriculture has led to the proposal of a coupled soil-mulch model to clarify the dynamics of pesticides under different no-till scenarios.

Céréale moissonnée dont la paille n'est pas récoltée, mais broyée sur place pour être enfouie lors des pratiques culturales suivantes.. © INRA, CAUVIN Brigitte
Updated on 06/25/2015
Published on 04/10/2015

Conservation agriculture, which is based on a reduction in soil tillage, direct sowing and plant cover, is growing in popularity throughout the world but may involve a greater use of herbicides.  Under a no-till system, the presence of mulch, or in other words plant residues from previous crops, is a determinant element in the different processes that control the fate of pesticides.

The interception of pesticides by mulch favours their localisation in harvest residues.  Their persistence is controlled within the mulch by retention processes through adsorption, microbial transformation and transport by leaching, the mechanisms of which are specific to mulches when compared to similar mechanisms in soils.

The aims of this work were to better understand these different processes, to establish the bases to model each of the processes, and assemble their mathematical representation within the same model.  A combination of experimental methods to enable the parallel monitoring of both mulch decomposition and the fate and transport of pesticides at the scale of soil columns under different water regimes, made it possible to test the different modelling hypotheses and obtain values for certain parameters.

 

Processes dependent on mulches and the microbial biomass ensuring their degradation

This work showed that:

•the adsorption coefficient of pesticides in mulches can be described by a function linked to their biochemical quality, which depends on their type and state of decomposition;

•pesticide degradation is proportional to the microbial biomass decomposing the mulches on the surface;

•their interception by a mulch, and their release from the mulch into the soil, can be simulated using a soil-mulch-atmosphere transfer model;

•analysis of the sensitivity of the model indicated that levels of pesticide leaching are sensitive to the water retention capacity of the mulch used and the time to onset of the first rain after pesticide application.

 

Towards a generalisation of the model

In time, the use of other experimental data obtained in the field, and the conduct of simulations for different scenarios regarding mulch quality and pesticide application practices will enable the generalised use of this model through its integration in the Sol Virtuel (Virtual Soil) platform.

 

This work was carried out in the context of a thesis project funded by the PEPITES project - Ecological processes and technical and social innovation processes in conservation agriculture (Processus écologiques et processus d’innovation technique et sociale en agriculture de conservation).

This model was first used in the context of the CIREPPE project: Undersown crops to reduce pesticide losses (Cultures intermédiaires pour réduire les pertes de pesticides).

These efforts, and their results, was one of the highlights of work by the Versailles-Grignon Research Centre during 2014.

Find out more

Aslam S., P. Benoit, F. Chabauty, V. Bergheaud, C. Geng, L. Vieublé-Gonod, P. Garnier. 2014. Modelling the impacts of maize decomposition on glyphosate dynamics in mulch. European Journal of Soil Science 65: 231.

Aslam S., A. Iqbal, M. Deschamps, S. Recous, P. Garnier, P. Benoit. 2015. Effect of rainfall regimes and mulch decomposition on the dissipation and leaching of S-metolachlor and glyphosate: a soil column experiment. Pest Management Science 71: 278.