Interception and Retention of Atrazine by Wheat (Triticum aestivumL.) Stubble

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Abstract
Atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] retention by standing and flat wheat (Triticum aestivum L.) stubble was determined over time. Immediately following an application of 1.7 kg/ha atrazine, approximately 60% of the herbicide had been intercepted by the stubble and 40% was found in the underlying soil. After 3 weeks and 50 mm of rainfall, atrazine on standing and flat stubble had decreased by 90 and 63%, respectively, while atrazine in the soil increased nearly twofold. No atrazine was found in stubble 9 weeks after application, and only 17% of that originally applied remained in the upper 4 cm of the soil. Successive alternate-day applications of 12.5, 25, or 50 mm water on 14C-atrazine retention by stubble was determined. Atrazine loss from stubble was greatest during the first water application, but there was no linear relationship between water application rate and retention of the herbicide. Atrazine loss from stubble decreased significantly following the second water application in all treatments. The amount of water applied did not influence atrazine loss following the third washing. Subsequent loss after the fourth, fifth, sixth, and seventh washings was not significant at any water application volume. After the seventh washing, atrazine residues were greatest on stubble which had received the least amount of water.