TEMPERATURE EFFECTS ON IMAZAQUIN SOIL BIOAVAILABILITY, UPTAKE, AND METABOLISM IN CORN (ZEA-MAYS)

Growth chamber experiments were conducted to determine the effects of soil temperature on the response of corn to imazaquin soil residues. I n a silt loam soil, 24/30 C (night/day) or 18/24 C soil temperatures c aused greater inhibition of shoot growth than 12/18 C soil temperature . However, in a sandy loam soil, inhibition of corn shoot growth was m aximal at 18/24 C, and there was no difference in shoot-growth inhibit ion between the lowest and highest temperatures. Higher soil temperatu res caused greater root-growth inhibition in the sandy loam soil but n ot in silt loam soil. Soil temperature did not affect C-14-imazaquin u ptake from either soil. Higher soil temperatures increased the translo cation of imazaquin from root to shoot tissue in both soils. In the sa ndy loam soil, imazaquin metabolism in root tissue decreased as soil t emperature increased, with twice as much parent herbicide recovered fr om roots of plants grown under the highest compared with the lowest te mperature treatments. Soil temperature had no effect: on imazaquin met abolism in shoot tissue. Longer-term experiments (22 d) were conducted with the sandy loam soil to determine the effect of changes in air te mperature on corn response to imazaquin soil residues. Plants exposed to 24/30 C for 7 or 14 d of the final 14-d growing period showed great er inhibition of shoot growth compared with plants maintained at 12/18 C. Uptake and translocation of C-14-imazaquin to shoots was greater i n plants maintained at 24/30 C throughout the final 14-d period than i n plants maintained at 12/18 C. Plants grown for 7 d at 24/30 C during the final 14-d period either preceding or following 7 d growth at 12/ 18 C showed increased translocation of imazaquin to shoots but no diff erence in imazaquin uptake compared with plants maintained at 12/18 C. Neither air nor soil temperature treatments had any effect on imazaqu in concentration in soil water.