Fertilization strategies affect phosphorus forms and release from soils and suspended solids

Area of Science:

• Agricultural Science
• Environmental Chemistry
• Soil Science

Background:

• Soil phosphorus (P) release in surface runoff is a major driver of agricultural eutrophication.
• Fertilizer inputs, including mineral fertilizers and organic amendments, critically influence P dynamics in soils.

Purpose of the Study:

• To evaluate the forms and availability of P in bulk soils and suspended solids (SS) under different long-term fertilization regimes.
• To understand how P surplus and soil management affect P lability and exchangeability in erodible particles.

Main Methods:

• A water dispersion test mimicking rain events was used to generate suspended solids (SS) from maize-cultivated soils.
• Hedley sequential P fractionation and isotopic exchange kinetics were employed to analyze P forms and availability in bulk soils and SS.
• Soils were treated for 15 years with mineral NPK, mineral PK, bovine slurry + P (S), or manure + P (M).

Main Results:

• P surplus increased in the order: NPK < PK < S < M.
• Labile P forms increased with P surplus, comprising up to 15% of total P in bulk soil and 25% in SS.
• SS showed selective enrichment of labile P forms, leading to rapid and intense P exchangeability.

Conclusions:

• Long-term fertilization with organic amendments (slurry, manure) results in higher P surplus and labile P forms compared to mineral fertilizers.
• Suspended solids are enriched in labile P, increasing the risk of P loss and eutrophication.
• The mechanisms controlling P forms and exchangeability differ between mineral fertilizer treatments (P saturation of oxides) and manure treatments (soil carbon content).