Phosphate stable oxygen isotope variability within a temperate agricultural soil

Area of Science:

• Environmental Science
• Soil Science
• Geochemistry

Background:

• Intensively managed agricultural grasslands are crucial for nutrient cycling.
• Understanding spatial variability of soil phosphorus (TP) and its fractions is vital for nutrient management.
• Stable oxygen isotopes in phosphate (δ18OPO4) offer insights into soil processes but their field-scale variability is understudied.

Purpose of the Study:

• To spatially analyze soil total phosphorus (TP), acid-extractable phosphate (HCl-PO4), and phosphate oxygen isotope ratios (δ18OPO4) at a field scale.
• To investigate the spatial autocorrelation of δ18OPO4.
• To assess the relationships between δ18OPO4 and soil properties (HCl-PO4, elevation, slope) globally and locally.

Main Methods:

• Spatial analysis of soil samples from an agricultural grassland.
• Measurement of total phosphorus (TP) and acid-extractable phosphate (1 M HCl) concentrations.
• Determination of stable oxygen isotope ratios (δ18OPO4) in extracted phosphate.

Main Results:

• Soil TP ranged from 736 to 1952 mg P kg−1, with 12–48% as HCl-extractable phosphate (HCl-PO4), showing a strong positive correlation.
• The δ18OPO4 ranged from 17.0 to 21.6‰ (mean 18.8‰).
• δ18OPO4 exhibited no significant spatial autocorrelation and weak global relationships with HCl-PO4, elevation, and slope, though local relationships varied.

Conclusions:

• Field-scale variability of soil δ18OPO4 is not strongly spatially structured.
• Local variations in the relationship between δ18OPO4 and soil properties suggest influence of soil class or historical management practices.
• This study is the first to assess field-scale δ18OPO4 variability, highlighting potential for localized insights into soil phosphorus dynamics.