ATRAZINE PERSISTENCE AND RESIDUE EFFECTS ON ROTATION CROPS

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Abstract
Field studies on Prince Edward Island (P.E.I.) loam to fine sandy loam soils from 1977 to 1980 determined the rate of breakdown of atrazine and soil residue effects on crops grown in rotation with silage corn (Zea mays L.). The rate of breakdown was rapid during the first 30 days after application with an estimated half-life of 23 days when averaged over rates and years. Timothy (Phleum pratense L.) and red clover (Trifolium pratense L.) were most sensitive to atrazine residues; yields of red clover were reduced significantly from the 1.13-kg/ha rate and of timothy after the 2.25-kg/ha rate. Yields of winter rye (Secale cereale L.) broadcast seeded in standing corn in August and barley (Hordeum vulgare L.) seeded the next spring were not affected, or reduced only slightly, by atrazine residues from initial applications of 1.13 kg/ha but showed significant yield losses at the 2.25- and 4.50-kg/ha rates. Alfalfa (Medicago sativa L.) seeded the next spring after atrazine use was tolerant of residues showing significant yield losses only at the 4.50-kg/ha rate. In this study, atrazine applied at 1.13 kg/ha in silage corn was sufficiently broken down to permit production of all crops studied except red clover.Key words: Atrazine, residue, clover (red), timothy, alfalfa, rye (winter), barley

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