Effect of nitrapyrin on nitrapyrin residues and nitrate content in red beet roots fertilised with urea

The effect of nitrapyrin [2-chloro-6-(trichloromethyl)pyridine] application on nitrapyrin residues and nitrate content in red beet (Beta vulgaris L. var. conditiva) roots and in soil fertilised with urea was studied during the 1977 growing season. The nitrapyrin residues in roots were on 15 August between 0.00–1.19 μg g^?1 and on 1 October between 0.00–0.45 μg g^?1 (dry weight basis) correlating significantly r = 0.99, P<0.01) to the rates of nitrapyrin applied on 8 June (0–34 kg ha^?1). The content of nitrapyrin in roots decreased in autumn having in August-September a ‘biological half-life’ of 3 weeks. In soil the same parameter was in July-September more than 4 months. The ratio of nitrapyrin to its main breakdown product varied in soil between 3.5–24.8 and in red beets between 0.6–1.4. Neither of these compounds were found in processed canned red beets. Nitrapyrin treatment decreased the nitrate content in both soil and beets. The inhibitor application of 18 kg ha^?1 caused the highest reduction of the NO₃-nitrogen content in beets, the average values on dry weight basis being 0.51–0.34 mg g^?1 for 0–18 kg ha^?1 nitrapyrin application, respectively. The reduction of NO₃-nitrogen in beets from its level of 15 August to its September level was 44%. After 5 September the reduction of the nitrate level in beets was not significant.