4. Conclusions
Mesotrione dissipation in an agricultural soil was affected by the
organic residue used as amendment when a low herbicide dose was applied.
Higher doses decrease the dissipation of herbicide in unamended
and amended soils, with the decrease being more significant in the SSamended
soil. The addition of organic amendments to soil positively
or negatively modified the different soil microbial parameters analyzed.
The biomass values increased in the amended soils compared to the unamended
one in all cases, and increased over the incubation period in
the SS-amended soil. Initially, the application of higher mesotrione
doses increased the biomass values in all the soils. However, DHA increased
only through the addition of compost to the soil, and it was
stimulated when low doses of mesotrione were applied, but decreased
in all the soils when higher doses of herbicide were applied. At time
0 days, respiration increased in the SS-amended soils compared to the
unamended and C-amended soils. The application of mesotrione had
no effect on soil respiration for the unamended and SS-amended soils,
and at time 28 days only the C-amended soil treated with the highest
mesotrione dose had a higher respiration value compared to the untreated
C-amended one. The results indicate that the highest concentration
of mesotrione had an effect on soil microbial abundance and
activity. Studies concerning the effects of soil management (amendment
and pesticide application to agricultural soils) on microbial
parameters are important for maintaining soil quality and its functioning.
Likewise the study of the effect of amendment and pesticide application
on soil microbial structure would be useful to complete our
knowledge on this subject.