Biogeochemistry of soil inorganic and organic phosphorus: A compositional analysis with balances

• Soil P was sequentially fractionated in 138 mineral and organic soil samples.
• A hierarchy of sound balances between components of the P cycle was elaborated.
• Phosphorus biogeochemistry depended on soil genesis and land management.
• Soils at high P risk showed primarily inorganic P misbalance.
• Sustainable terrestrial ecosystems require balancing P inputs with soil buffer.

Present soil P cycling models and the related ecosystem services such as P retention deny the special properties of compositional data resulting from closure and leading to methodological inconsistencies and pathological behavior. Our objective was to elaborate and interpret a hierarchy of supervised balances between components of the soil P cycle computed as isometric log ratios (ilr) to avoid biases when assessing P risk in managed terrestrial ecosystems. Fourty-one acid sandy soils, 56 acid to neutral loamy to clayey soils and 41 acid organic soils (10 fibric or hemic peat and 31 sapric ‘moorsh’ or ‘muck’ materials) were collected in Québec, Canada, analyzed for resin-P, NaHCO3-P, NaOH-P and residual P fractions, arranged into a hierarchy of sound balances and classified for the risk of P leaching. Pathological behavior was shown by spurious correlations between P fractions varying in magnitude, sign and significance depending on what was considered as the “whole” (e.g. total P or soil dry matter). Discriminant analysis across unbiased balances showed that the balances related to soil genesis dominated P biogeochemistry. Soils at low or high P risk for P leaching showed contrasting degrees of Po and Pi loads. Low- and high-P risk loamy and clayey soils differed significantly for balances relating labile to slowly available Pi, as well as those relating Pi to Po. Low- and high-P risk sandy soils were contrasted by the balance relating oxalate-extractable Al and Fe. Peat and ‘moorsh’ materials differed in most ilrs. As soils loose ecosystem services provided by soil P geochemical and biological pools in terms of P-fractions balances, terrestrial ecosystems become less sustainable.

Soil P biogeochemical composition schematized in a balance domain (ilr = isometric log ratio) relating components of the P cycle displayed in a concentration domain (Fv = filling value to measurement unit) in buckets.Figure optionsDownload as PowerPoint slide