Pesticide dynamics in agroecosystems: Assessing climatic and hydro-physical effects in a soybean cycle under no-tillage

The high rate of No-Tillage (NT) adoption in Argentina has been followed by conspicuous application of herbicides due to RR crops selection and recently due to weed resistance. In addition, no-tillage in the Rolling Pampa (Argentina) with absence of crop rotation and scarce crop residues, led to physical degradation (low infiltration rates, platy structure development) having strong implications on water dynamics and the risk of soil and water contamination. Several factors can influence the mobility of pesticides in the landscape. However, measurement of soil hydro-physical and climate traits as determinants of pesticide dynamics are still scarce. In this study, pesticides from soil and runoff (Glyphosate, AMPA, S-Metolachlor, Sulfentrazone), and hydro-physical and climatic variables were measured at the field in an entire soybean cycle under NT. Temporal dynamics of runoff and saturated hydraulic conductivity was measured by rainfall simulations and disc permeameters together with soil bulk density, soil moisture, crop residues, rainfall and rainfall erosivity. Besides, soil structure was evaluated through cultural profile method. In the Vertic Argiudoll (silty clay loam) pesticides mobility were related to the number of days after agrochemical application modulated also by heavy natural rainfalls occurred during the experiment that lowered agrochemical concentration mostly in runoff. Temporal hydro-physical properties and spatial soil structural variability, together with strong climatic events governed runoff process affecting pesticides mobility while no strong pesticide accumulation in the plots was observed in this study due to low saturated hydraulic conductivity, high runoff coefficients and poor soil structural traits. Thus, the selection of appropriate agricultural management is a key factor to modify hydro-physical top soil dynamics to change hydrological partition from horizontal to vertical fluxes, in particular in soils with poor structural condition.