Impact of soil moisture on metsulfuron-methyl residues in Chinese paddy soils

The present study was conducted to examine the dynamics of the extractable and bound residues and the mineralization rate of 14C-metsulfuron-methyl in six Chinese paddy soils held at 20, 40, and 50% water-holding capacity (WHC) and 35 °C for 84 days. The results showed that extractable residues were higher, but bound residues and mineralization rates of 14C-metsulfuron-methyl were lower in the soil with a higher pH than in the acid soils. Increasing the soil moisture contents significantly enhanced mineralization of 14C-metsulfuron-methyl in the soils. The half-lives of 14C-metsulfuron-methyl at 50, 40, and 20% WHC were 73–267, 110–385, and 165–462 days, respectively. Furthermore, the dynamics of the extractable and bound residues of 14C-metsulfuron-methyl were affected significantly by soil moisture. The level of the extractable residues increased with increasing moisture contents during the initial 14 days after metsulfuron-methyl application (DAA) in all soils, and the trend was maintained for the alkaline soil from 28DAA to 84DAA, but the opposite was observed for the five acidic soils. The formation of the bound 14C-metsulfuron-methyl residues decreased when soil moisture contents were increased in all the soils over the whole incubation period. The data obtained in the present study indicate that soil moisture would not only affect microbial activity, but also alter the distribution of metsulfuron-methyl residues between extractable and bound fractions, both of which may affect metsulfuron-methyl degradation.