Biodiversity-safeguarding threshold for urea-fertilizer application on paddy fields: Protozoa-based toxicity tests

Area of Science:

• Environmental Science
• Ecotoxicology
• Agricultural Science

Background:

• Excessive urea fertilizer application poses ecological risks to paddy fields, threatening sustainable agriculture and biodiversity.
• Current thresholds for urea application lack data-based validation, particularly concerning microbial communities.
• Protozoa are identified as nitrogen-sensitive organisms, making them potential bioindicators for ecological risk assessment.

Purpose of the Study:

• To establish scientifically validated thresholds for urea application in paddy fields to mitigate ecological risks.
• To identify sensitive indicator species for monitoring urea toxicity in aquatic ecosystems.
• To provide a basis for developing urea fertilizer reduction protocols for biodiversity preservation.

Main Methods:

• Conducted acute and chronic urea toxicity tests on eight aquatic species, including protozoa.
• Utilized species sensitivity distribution curves to estimate predicted no-effect concentrations (PNEC).
• Established short-term and long-term safety thresholds for urea application based on field area and surface water height.

Main Results:

• Blepharisma sp. demonstrated the highest sensitivity to urea, identifying it as a suitable bioindicator.
• The predicted no-effect concentration (PNEC) was estimated using species sensitivity distribution.
• A short-term safety threshold of 87.7 mg/L (43.85 kg urea/hectare) and a long-term threshold of 5.02 mg/L were established for the studied black soil paddy field.

Conclusions:

• Blepharisma sp. can serve as an effective indicator species for assessing urea toxicity in paddy fields.
• The established urea application thresholds provide crucial data for sustainable agricultural practices.
• This research supports the development of urea reduction strategies to safeguard paddy field biodiversity.