Glyphosate behavior in rice paddy fields across different rotation systems

Area of Science:

• Environmental Science
• Agronomy
• Soil Science

Background:

• Intensified irrigated rice production necessitates evaluating pesticide environmental impacts.
• Glyphosate (GLY) and its metabolite aminophosphonic acid (AMPA) are widely used herbicides.

Purpose of the Study:

• To investigate the behavior and persistence of glyphosate (GLY) and aminophosphonic acid (AMPA) in irrigated rice production systems.
• To assess the influence of different agricultural intensification scenarios on herbicide fate.

Main Methods:

• Long-term experimental (LTE) site with four rice rotations: continuous rice (R_C), rice-soybean (R-S), rice-short term pasture (R-P_S), and rice-long term pasture (R-P_L).
• Glyphosate applied twice in all rotations; soil and floodwater sampled to determine GLY and AMPA concentrations and decay rates.
• First-order exponential decay and kinetic models used to analyze degradation.

Main Results:

• Glyphosate and AMPA levels were influenced by application timing and frequency, but not decay rates.
• Glyphosate soil half-life (DT₅₀) was 31.5 days during the non-flooded phase and 5.3 days in floodwater.
• AMPA showed slower decay in floodwater (DT₅₀ ≈ 7.4 days).
• Rice-pasture rotations (R-P_S, R-P_L) exhibited lower GLY residues compared to R_C and R-S systems.

Conclusions:

• Land use intensification scenarios significantly affect background GLY levels in soil.
• Rice-pasture based rotations offer a potentially more sustainable approach by reducing herbicide residues.
• Findings inform sustainable agricultural and water management practices in rice production.