Rapid incidental phosphorus transfers from grassland.

Area of Science:

• Environmental Science
• Soil Science
• Water Quality Management

Background:

• Britain's high rainfall creates a risk of direct phosphorus (P) loss after fertilizer or manure application.
• Phosphorus contributes to water body eutrophication, yet incidental P transfers are understudied.
• Incidental P transfers are a significant pathway for P loss to aquatic ecosystems.

Purpose of the Study:

• To experimentally investigate incidental phosphorus (P) transfers from different P sources.
• To quantify P losses in composite overland and subsurface flow under simulated rainfall conditions.
• To assess the impact of P source type on P export and concentration.

Main Methods:

• Lysimeter plots (3 x 10 m) were used to simulate rainfall and measure P loss.
• Treatments included triple super phosphate (TSP), dairy slurry, a mix of TSP and slurry, and no P (Zero P).
• P sources were applied to wet soil at 29 kg ha(-1), followed by 48.8 mm of rainfall over 169 hours.

Main Results:

• Total phosphorus (TP) exports ranged from 1.8 to 2.3 kg ha(-1) within 169 hours.
• A single 4-hour rainfall event with overland flow accounted for 33-46% of total P loads.
• Discharge concentrations peaked at 11000 microg TP L(-1) for TSP and TSP + Slurry, and 7000 microg TP L(-1) for Slurry.
• Even subsurface flow showed TP concentrations exceeding 3000 microg TP L(-1) for all P-amended treatments.
• Incidental TP concentrations were up to 110-fold higher than eutrophic levels in inland waters.

Conclusions:

• Short-term management of phosphorus (P) application timing is crucial for mitigating P loss.
• Different P sources (TSP, slurry) result in varying P forms and export dynamics.
• Urgent management strategies are needed to reduce incidental P transfers and protect water quality.