Dissipation of Topramezone in Maize Growing Soils of Telangana State, India
Ramprakash T *
AICRP on Weed Management, PJTAU, Rajendranagar, Hyderabad-30, India.
Padmaja B
AICRP on Weed Management, PJTAU, Rajendranagar, Hyderabad-30, India.
Vijay Sree Chopde
AICRP on Weed Management, PJTAU, Rajendranagar, Hyderabad-30, India.
T Balasrikanth Reddy
AICRP on Weed Management, PJTAU, Rajendranagar, Hyderabad-30, India.
*Author to whom correspondence should be addressed.
Abstract
Understanding the kinetics and mechanisms of herbicide degradation under region-specific soil and climatic conditions is essential for optimizing application schedules and mitigating environmental risk. Persistence and dissipation of topramezone were quantified in two contrasting Telangana soils - red sandy loam (Alfisol) and black clay (Vertisol)—to inform leaching risk and rotation safety under tropical conditions. The present study contributes to a better understanding of topramezone persistence and movement in Indian soils and help refine herbicide use strategies to minimize environmental and crop-rotation risks in maize-based systems. Composite surface soils were characterized (pH, EC, organic carbon and CEC) and incubated at 27 ± 0.2 °C after fortification to 0.2 mg kg⁻¹. Residues were measured at 0–135 days using validated HPLC–UV (LOD 0.007 mg kg⁻¹; LOQ 0.020 mg kg⁻¹; recoveries 84.8–91.2%). The dissipation kinetics of topramezone were analysed assuming a first-order rate equation. The coefficient of determination (R²) was used to assess model fit, and only regressions with R² > 0.90 were accepted. Initial detected amount (2 h after application) was 90.61 µg 10 g⁻¹ in the red soil and 92.12 µg 10 g⁻¹ in the black soil. Concentrations declined to 40.21 and 38.65 µg 10 g⁻¹, respectively, by 135 days. Among linear, polynomial, logarithmic and exponential models, first-order kinetics best described dissipation with excellent fits (R² > 0.97). Rate constants (k) ranged 0.0057–0.0069 day⁻¹, giving DT₅₀ values of 121.6 days (red) and 100.4 days (black). When interpreted alongside sorption behaviour (weak-acid pKa = 4.06; moderate–low sorption that decreases with increasing pH), the data indicate a high leaching potential, especially in neutral–alkaline, higher-pH settings. The findings reinforce that environmental variables, particularly soil moisture and temperature, strongly influence degradation kinetics of weakly acidic, HPPD-inhibiting herbicide. Management strategies involving proper irrigation scheduling and rotation planning are essential to minimize the risk of residual injury from topramezone residues in tropical agroecosystems. Overall, soil type and moisture regime exert first-order control on topramezone persistence and, by extension, on leaching risk under semi-arid Indian conditions.
Keywords: Degradation, first-order kinetics, half-life, leaching potential, soil moisture regime and Topramezone dissipation