Phosphorus saturation in spodosols impacted by manure

Area of Science:

• Soil Science
• Environmental Chemistry
• Agronomy

Background:

• Animal manures contribute significant phosphorus (P) to soils, raising concerns about potential dissolved P loss via runoff and leaching.
• The degree of phosphorus saturation (DPS) is a key metric indicating a soil's P mobilization risk, relating extractable P to its sorption capacity.

Purpose of the Study:

• To assess P release potential in Spodosols from South Florida dairy systems using DPS.
• To evaluate two DPS indices (DPS-1 and DPS-2) as predictors of water-extractable P.

Main Methods:

• Calculated DPS-1 (Mehlich 1-extractable P / oxalate-extractable Fe + Al) and DPS-2 (Mehlich 1-extractable P / Mehlich 1-extractable Fe + Al) in various soil horizons.
• Compared DPS values across land uses: intensive/holding (high manure impact) vs. pasture/forage/native (low manure impact).
• Analyzed soils from active and abandoned dairy systems in Florida's Lake Okeechobee watershed.

Main Results:

• Soils in heavily manure-impacted areas (intensive, holding) showed higher DPS-1 values than minimally impacted areas (pasture, forage, native).
• Both DPS-1 and DPS-2 were significantly correlated (P = 0.0001) with water-extractable P across all soil horizons.
• Higher DPS values were observed in A and E horizons of impacted soils.

Conclusions:

• The degree of phosphorus saturation (DPS) is a reliable indicator of P loss potential from Spodosols.
• Both DPS-1 and DPS-2 indices effectively predict the risk of phosphorus mobilization in agricultural soils.
• Management strategies focusing on DPS can help mitigate phosphorus pollution from agricultural lands.