[14C-extractable residue, C-bound residue and mineralization of 14C-labeled metsulfuron-methyl in soils]

The purpose of the present study was to investigate 14C-extractable residue(14C-ER), 14C-bound residue(14C-BR) and mineralization of 14C-labeled metsulfuron-methyl in soils. The main factors affecting 14C-BR formation and the distribution pattern of 14C-BR in humus were also discussed in details. The results were as follows: (1) The total 14C-ER content of 14C-metsulfuron-methyl in seven kinds of soil was positively related to soil pH and negatively related to clay content significantly during the initial 20 days of incubation, however, only positively relation to soil pH was found after 30 days of incubation. Moreover, the half-life values of 14C-metsulfuron-methyl parent compound derived from 14C-ER in soils tested ranged from 13.3 to 66.6 days. The degradation rate coefficient lambda (day-1) was negatively related to soil pH. (2) The 14C-BR content of 14C-metsulfuron-methyl in soils was significantly negatively related to soil pH and positively related to the clay content during the initial 20 days of incubation, but only was significantly negatively related to soil pH after 30 days incubation. Again, the soil pH was found to be the dominant factor affecting BR formation of 14C-metsulfuron-methyl among the basic properties of soil. The maximum content of 14C-BR of 14C-metsulfuron-methyl in the soils accounted for 19.3%-52.6% of applied amount. (3) During the whole periods of the incubation, the 14C-BR of 14C-metsulfuron-methyl in the soils was found to be mainly associated with fulvic acid and humin. The relative percentage of 14C-BR in fulvic acid was higher than in humin, while the content of the 14C-BR distributed in humic acid only account for less than 1% of applied amount. Therefore, fulvic acid played an important role in the process of BR formation of 14C-metsulfuron-methyl. (4) About 12.9%-27.0% of applied amount of 14C-metsulfuron-methyl was mineralized to 14CO2 through opening 14C-triazine ring in soils tested after 180 days of the incubation. It was difficult for 14C-metsulfuron-methyl to mineralize to 14CO2 in an alkaline soil.