Fate of metolachlor under subirrigation in a sandy soil: A lysimeter study

A three-year field lysimeter study was conducted to investigate the role of subirrigation systems in reducing the risk of water pollution from metolac hlor (2-chloro-N-(2-ethyl-6-methlphenyl)-N-(2-methoxy-1-methylethyl)acetami de). Nine large PVC lysimeters, 1 m long x 0.45 m diameter, were packed wit h a sandy soil. Three water table management treatments, i.e. two subirriga tion treatments with constant water table depths of 0.4 and 0.8 m, respecti vely, and a free drainage treatment in a completely randomized design with three replicates were used. Corn (Zea mays L.) was grown in each lysimeter, and at the beginning of summer of each year metolachlor was applied, at th e locally recommended rate of 2.75 kg a.i/ha. Soil and water samples were c ollected at different time intervals after each natural or simulated rainfa ll event. Metolachlor was extracted from these samples and analyzed using G as Chromatography. Results obtained in this three year study, (1993-1995), lead to the conclus ion that metolachlor is quite mobile since it leached to a depth of 0.85 m below the soil surface quite early in the growing season. Metolachlor conce ntrations decreased with depth as well as with time. The shallower water ta ble in the 0.4 m subirrigation treatment showed less residues in the soil s olution than that of other treatments. However, a mass balance study, suppo rted by an independent laboratory investigation, shows that water table man agement, statistically, has no significant effect on the reduction of metol achlor residues in sandy soils.