Laboratory studies were conducted to determine the effect of rainfall
timing and antecedent moisture on atrazine leaching through intact soi
l cores taken from no-till and conventional-till corn fields. Simulate
d rainfall was applied to no-till and conventional-till cores 1 to 14
d after atrazine application and, in a second study, one d after atraz
ine was applied to no-till and conventional-till cores at 1 to 800 kPa
soil moisture. Increasing the lag time between atrazine application a
nd rainfall from one to 14 d reduced the amount of atrazine leached by
about 50% for both no-till and conventional-till soil cores. During t
he same time period, the amount of atrazine adsorbed to soil increased
by about 30% for both tillages. Soil dryness (antecedent moisture) at
the time of atrazine application had no effect on the amount of atraz
ine leached through conventional-till cores. However, leaching decreas
ed in no-till cores as antecedent moisture decreased from 1 to 33 kPa;
drying to 800 kPa had no further effect. The leaching rate of atrazin
e was much higher for the initial 0.5 pore volume than for the next 1.
5 pore volume at all rainfall timing and antecedent moisture levels. T
his behavior is indicative of preferential transport.