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Fate of ametryne in soil, nutrient solution-sugarcane and soil-sugarcane systems

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Title:Fate of ametryne in soil, nutrient solution-sugarcane and soil-sugarcane systems
Authors:Goswami, Kishore Puri
Spraying and dusting residues in agriculture
Sugarcane -- Analysis
Date Issued:1972
Abstract:Ametryne (2-methylthio-4-ethylamino-6-isopropylamino-~-triazine) is used in sugarcane, pineapple and banana cultivation for weed control mainly in the tropics, and very little has been published concerning its fate in soil and sugarcane. This investigation was carried out utilizing ring-14C ametryne to determine its degradation and metabolism and to develop a 14C-balance account for each experiment. A simple procedure was developed for the simultaneous extraction of ametryne, atrazine and hydroxyatrazine (HA) in acidified methanol from soil by shaking, and quantitative separation of HA by liquid-liquid partitioning. Quantitative extraction was achieved when the pH of soil extract (soil/solvent = 1/10) was between 2.0 and 2.5, without causing hydrolysis of the two parent triazines to HA during the extraction. HA was quantitatively partitioned in the aqueous phase by first treating the soil-extract with 0.25N HCl (HC1/extract = 0.25), mixing with water (water/extract = 1) and then chloroform (chloroform/extract = 5). Degradation and metabolism of ring_14c ametryne. ring-14C HA and ethyl-14C HA were determined for 30 days in a nutrient solution-sugarcane system. Sugarcane roots rapidly converted ametryne to more polar compounds (90% at 30 days); the major degradation products were dealkylated ametryne (32.9%) at 20 days and 2-methylthio-4,6-diamino-~triazine (12.5%), and ammeline (34.4%) at 30 days. Metabolism of ring14C ametryne, ring_14c HA and ethyl-14C HA to 14CO2 by sugarcane was confirmed for the first time; of the absorbed 14c, 1.7%, >8.0% and >23.0% 14CO2 were evolved respectively from ping_14C ametryne, ring_14C HA and ethyl-14C HA treated plants. In the same study a volatile 14C metabolite (1.9% of applied 14C) was discovered for the first time in the condensed transpired water from ametryne treated sugarcane; it was not 14CO2 but a basic, water soluble compound. No 14Cwas found in the transpired water from HA treated plants. Ametryne and HA were degraded through different mechanisms in sugarcane. Ametryne was not degraded to HA by sugarcane, but cane was able to metabolize HA faster than ametryne. Proposed degradation pathways for HA and ametryne have been presented. Degradation of ametryne-14C in sterilized and non-sterilized soils was measured for 60 days. In non-sterilized Hilo and Molokai soils, 36 and 25% ametryne was converted to polar-products against 4.2 and 4.9% in the sterilized soils respectively; evolved 14CO2 was 0.19 and 0.08% respectively in non-sterilized soils. The concentration of the polar-products, and not of ametryne, was the rate-limiting step for 14CO2 evolution. Assimilated-14C was 19 and 9% respectively in non-sterilized Hilo and Molokai soils, and 0.1% in sterilized soils. Ametryne degradation in a Molokai soil-sugarcane system was determined for 60 days with soil-root and shoot components enclosed separately. The respective percent 14C-constituents measured at 60 days in soil-root and bare soil were: polar-products, 84.1 and 19.5; 14C02 evolved, 4.04 and 0.08; and biomass, 19.4 and 1.4. The shoot evolved only 0.03% 14CO2. Nearly 5% of the absorbed-14C was volatilized from the shoot and measured in the condensed transpired water. Ametryne was degraded both through N-dealkylation and 2-hydroxylation in soil. The major discoveries were: (1) Sugarcane plants metabolized ring-14C ametryne, ring-14c HA and ethyl-14C HA to 14CO2. (2) A volatile 14C-metabolite was present in the condensed transpired water from ametryne treated plants but not from HA treated plants. (3) Ametryne and HA were degraded by sugarcane through different mechanisms. (4) Ametryne degradation in bare soil was mainly (N-dealkylation) a microbial process with limited simultaneous chemical hydrolysis. (5) Sugarcane roots accelerated ametryne degradation (N-dealkylation) by several fold in nutrient solution and in soil (2-hydroxylation). (6) Simultaneous extraction of HA and parent triazines from soil in acidic-methanol and partitioning of HA in chloroform with added water was quantitative.
Thesis (Ph. D.)--University of Hawaii at Manoa, 1972.
Bibliography: leaves [160]-168.
xii, 168 l illus. tables
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Appears in Collections: CTAHR Ph.D Dissertations
Ph.D. - Agronomy and Soil Science

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