Vegetated ditches as a management practice in irrigated alfalfa

Area of Science:

• Environmental Science
• Agricultural Science
• Ecotoxicology

Background:

• Organophosphate (OP) insecticides like diazinon and chlorpyrifos contaminate surface waters, particularly the San Joaquin River.
• Irrigation tailwaters are a primary pathway for OP pesticide runoff into aquatic ecosystems.
• Effective management strategies are needed to mitigate pesticide contamination from agricultural sources.

Purpose of the Study:

• To evaluate the efficacy of a vegetated tailwater return ditch in reducing chlorpyrifos runoff.
• To assess the impact of delayed irrigation on chlorpyrifos concentrations in surface water from flood-irrigated alfalfa.
• To provide data-driven insights for managing OP pesticide movement in agricultural watersheds.

Main Methods:

• Field study evaluating a constructed, vegetated irrigation tailwater return ditch.
• Comparison of chlorpyrifos concentrations in runoff from vegetated versus conventional tailwater ditches.
• Analysis of chlorpyrifos levels in relation to varying irrigation lag times (48-144 hours) after pesticide application.

Main Results:

• The vegetated ditch achieved a median chlorpyrifos concentration reduction of 38% in irrigation runoff.
• Conventional tailwater ditches showed only a 1% reduction in chlorpyrifos concentrations.
• No consistent reduction in chlorpyrifos tailwater concentrations was observed with irrigation lag times up to 144 hours.

Conclusions:

• Constructed vegetated tailwater ditches are a promising management practice for reducing off-site movement of chlorpyrifos.
• Delayed irrigation is not an effective strategy for mitigating chlorpyrifos runoff in flood-irrigated alfalfa systems.
• Implementing vegetated buffer systems can significantly improve water quality in agricultural watersheds affected by OP pesticides.