Gypsum amendment of agricultural fields to decrease phosphorus losses - Evidence on a catchment scale.

Area of Science:

• Agricultural Science
• Environmental Science
• Water Quality Management

Background:

• Agricultural runoff, particularly phosphorus (P), is a major contributor to coastal water pollution.
• Gypsum application to agricultural fields is a proposed cost-effective strategy to mitigate P and sediment loss.
• Understanding the long-term efficacy and environmental impact of gypsum amendments is crucial for sustainable agriculture.

Purpose of the Study:

• To evaluate the effectiveness of phosphogypsum application in reducing nutrient and sediment loads in coastal waters.
• To assess the duration of gypsum's impact on riverine fluxes of particulate P (PP), total suspended solids (TSS), and dissolved organic C (DOC).
• To compare P and sediment losses from gypsum-amended fields versus unamended fields.

Main Methods:

• Treatment of 1490 ha of clayey agricultural fields with phosphogypsum (4 t ha⁻¹).
• Monitoring of recipient river water quality using online sensors and sampling for 5 years post-amendment.
• Comparison of flux data with an upstream control area and pre-amendment data.

Main Results:

• Immediate and sustained reduction in riverine fluxes of PP, TSS, and DOC for at least 5 years.
• Significant decreases in PP (15%), TSS (25%), and DOC (8.9%) fluxes over the 5-year monitoring period.
• Amended fields showed substantially lower losses of PP (35%), TSS (59%), and DOC (64%) compared to unamended fields, indicating gypsum's effectiveness.

Conclusions:

• Gypsum application is a viable method for reducing P and sediment runoff from agricultural lands.
• The residual presence of gypsum in soil suggests a potential for long-term benefits, though efficiency may decrease over time.
• Variations in erodibility and spatial performance highlight the need for careful consideration of site-specific conditions when applying gypsum.