Soil Enzymatic Response to Nicosulfuron: A Preliminary Study in a Chernozem Typical to the Banat Plain, Western Romania

Nicosulfuron, despite being a post-emergence herbicide commonly used in corn crops to combat weeds, there is still little information on nicosulfuron toxicity for soil microbiota. Little information exists on the impact of nicosulfuron on the enzymatic activities of soil dehydrogenases (Deh), urease (Ure), catalase (Cat), and alkaline phosphatase (Alp). We used a multiple dose- and time point (7, 14, 21, and 28 days) study design to determine the effect of nicosulfuron on these parameters during the first 28 days post-application. The soil pH, electrical conductivity (EC), organic matter content (OM), water content, ammonium-nitrogen (NH4-N), nitrate-nitrogen (NO3-N), and available phosphate were also monitored. Ure was the most responsive enzyme to nicosulfuron. This herbicide exerted a transitory dose- and time-dependent inhibitory effect on Deh activity; maximum inhibition occurred at 14 days at doses from the normal recommended dose onward. For Ure, the maximal inhibitory effect started at 7 days of exposure to half the normal recommended dose and continued for another 14 days. The effect on Cat occurred later, whereas Alp activity was affected by nicosulfuron between 7 and 21 days but only for triple the normal recommended dose. OM showed the most consistent relationships with these parameters, being strongly positively correlated with Deh, Cat, and Alp activities. These results indicate that nicosulfuron may alter the soil metabolic activity, thus affecting its fertility.