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Microbial Degradation of Ametryn in Hawaiian Torrox and Hydrandept Surface Soils¹

ABSTRACT

Degradation of ring-¹⁴C ametryn in autoclaved and inoculated surface soils with added C and N sources was measured for 60 days in a ¹⁴C balance study. The study involved periodic analysis for (i) total methanol-extractable ¹⁴C, (ii) ¹⁴C-polar products separated from the methanol extract by liquid-liquid partitioning with chlorform, (iii) ¹⁴CO₂ evolution, and (iv) ¹⁴C-nonextractable residue by combustion. The results confirm that unlike the chemical breakdown of chloro-s-triazines, ametryn degradation in soil is predominantly a microbiological process which proceeds mainly through the initial N-dealkylation pathway with some simultaneous formation of hydroxyatrazine. Gas chromatographic analysis showed partitioning of two possible N-dealkylated products of ametryn metabolism into the aqueous phase of the chloroform/aqueous-methanol system. Less than 7% of the applied ametryn was lost in autoclaved soils, but ametryn was rapidly degraded in inoculated soils. Ametryn disappearance was much faster in the Hilo soil (Typic Hydrandept) with 8.7% remaining at 60 days than in the Molokai soil (Typic Torrox) with 63.7% remaining. The extremely high surface area and high organic matter content of the Hydrandept surface soil were considered conducive to higher microbial activity in this soil. The major fraction of ¹⁴C-degradation products was recovered in polar compounds with a lesser quantity residing in a nonextractable fraction; less than 0.2% was evolved as ¹⁴CO₂. Evolution of ¹⁴CO₂ at a given time was not governed either by the quantity of parent ametryn remaining nor by the concentration of polar products.

¹ Hawaii Agric. Exp. Sta. Journal Series no. 1786. Part of a dissertation submitted by the senior author in partial fulfillment of the requirements for the Ph.D. degree in Agronomy and Soil Science.

² Junior Soil Scientist and Professor, respectively. Department of Agronomy & Soil Science, Univ. of Hawaii, Honolulu, Hawaii 96822. The senior author is now Associate Professor of Soil Science, Punjab Agricultural Univ., Ludhiana, Punjab, India.

Received for publication August 2, 1974. Accepted for publication March 18, 1975.