Spatial variability in 14C-herbicide degradation in surface and subsurface soils

Area of Science:

• Environmental Science
• Soil Science
• Microbiology

Background:

• Agricultural herbicides like atrazine, isoproturon, and metamitron can impact soil ecosystems.
• Understanding their spatial variability in degradation is crucial for environmental risk assessment.

Purpose of the Study:

• To investigate the spatial variability of atrazine, isoproturon, and metamitron mineralization in French soil and subsoil.
• To determine factors influencing herbicide dissipation and mineralization rates, including soil properties and microbial activity.

Main Methods:

• Soil and subsoil samples from a 135-ha catchment were analyzed.
• 14C-labelled herbicides (atrazine, isoproturon, metamitron) were incubated under laboratory conditions.
• Overall microbial activity and specific herbicide degradation were monitored via CO2 evolution.
• Extractable and non-extractable residues were quantified.

Main Results:

• Herbicide dissipation half-life variability was low for atrazine and metamitron but high for isoproturon.
• Spatial variability in atrazine and metamitron dissipation was linked to mineralization rates.
• Isoproturon dissipation variability was mainly due to extractable residues.
• Herbicide degradation and microbial activity decreased significantly with soil depth.
• Atrazine mineralization was observed down to 2.5 meters.

Conclusions:

• Microbial degradation dynamics, not just soil properties, are key drivers of atrazine and isoproturon breakdown.
• Metamitron degradation is significantly influenced by sorption, particularly organic matter and clay content.
• Depth-dependent decline in microbial activity limits herbicide degradation in deeper soil layers.