DISPERSIVE TRANSFER AND PESTICIDE PROPAGATION IN A SUBMERGED RICE-FIELD

Vertical transfer of deuterated water observed in a small experimental plot of a submerged rice field showed that the water leaching process was complicated. The water flowed in several distinct regions, while others were hardly concerned with the leaching. This fingering may explain the transport towards a deep aquifer of an apparently small quantity of pesticides, despite their high degradation kinetics in the submerging water and their high adsorption onto the solid phase. Deuterated water concentrations were measured in the field with a .gamma. neutron probe; soil solutions sampled through porous cups were also analyzed with a laboratory device. Direct comparison of these 2 methods was made impossible by the variability of the flow paths. This variability was also an important limitation to the representativity of the results obtained by graphic representation.