Development of phosphorus sorption capacity-based environmental indices for tile-drained systems

Area of Science:

• Soil Science
• Environmental Chemistry
• Water Quality Management

Background:

• Phosphorus (P) loss to surface waters is an environmental concern, necessitating routine soil management strategies.
• Quantifying P sorption capacity (PSC) via laborious isotherms is impractical for regular decision-making.
• Pedotransfer functions (pedoTFs) offer a viable alternative for estimating PSC from standard soil properties.

Purpose of the Study:

• To develop and validate a pedoTF for estimating PSC.
• To evaluate PSC-based indices, specifically P saturation ratio (PSR) and soil P storage capacity (SPSC), for predicting P loss.
• To assess the relationship between these indices and soluble P concentrations in tile drain effluent.

Main Methods:

• Development of a pedoTF using soil aluminum and organic matter to predict PSC.
• Analysis of segmented-line relationships between PSR and soluble P in desorption assays and drainflows.
• Investigation of SPSC relationships with soluble P concentrations in both laboratory and field conditions.

Main Results:

• A pedoTF accurately predicted PSC (R² = .60) using soil aluminum and organic matter.
• Apparent PSR thresholds of 0.21 (desorption) and 0.24 (drainflow) were identified.
• SPSC showed linear relationships with soluble P, with negative values indicating potential P loss and positive values indicating low P concentrations.

Conclusions:

• PedoTF-derived PSC indices can effectively estimate subsurface soluble P loss potential.
• Identified index thresholds align with critical soil-test P levels for agronomic sufficiency.
• Agronomic P sufficiency thresholds may also serve as environmental P thresholds for water quality protection.