Atrazine Transport in Irrigated Heavy- and Coarse-Textured Soils, Part I: Field Studies

Abstract

Groundwater pollution in agricultural areas is a result of the excessive use of fertilizers and herbicides, and is a major concern in industrialized countries. In the Sorraia valley, Portugal, irrigated agriculture plays a very important role in the region's economy. This study was conducted to investigate the movement of atrazine through the soil profile, in two different but representative soils of this region, under irrigated conditions. Two plots, one located in a silty loam soil of recent alluvial origin and the second in a sandy soil of ancient alluvial formation, were selected for this study and were divided into three sub-plots for monitoring the movement of atrazine as a function of irrigation. The silty loam soil was under surface irrigation (furrowed level basin) during the summers of 1996 and 1997. The sandy soil was under surface irrigation (short blocked furrows) during the summer of 1996 and under sprinkler irrigation during 1997. Atrazine was applied to the surface at a rate of 1·2 kg a.i./ha in the silty loam soil, and at a rate of 1·0 kg a.i./ha in the sandy soil in Spring of 1996 and 1997. Several irrigations were applied during the months of July–September. The soil in each plot was monitored for water content and atrazine concentrations.The results of this study indicated that physical properties of the alluvial soil did not favour atrazine transport to deeper soil depths, but larger irrigations caused atrazine leaching to deeper depths. Similar observations in the sandy soil indicated that significant movement of atrazine occurred due to heavy rains a few days after atrazine application in 1996. The results also indicated that overirrigation resulted in leaching of atrazine in this coarse soil. For both alluvial and sandy soils, no residual accumulation of atrazine was observed during these two years. The translocation of atrazine was not found to be very high, and the highest atrazine concentrations were always found in the 0–10 cm depth soil layer for both soils.