Background and aims
Secondary minerals are known to provide sorption sites that contribute significantly to plant nutrient retention within the soil profile. The influence of mineral components on nutrient availability is however less certain in coarse-textured soils, where the abundance of clay minerals is low. The objective of this study is to identify important edaphic predictors of nutrient distribution in coarse-textured forest soils.
Methods
We measured base cations, nitrogen and phosphorus forms in the organic, mineral top- and subsoil horizons of podzols of southwestern Canada and investigated their relation to soil properties using simple and canonical correlation analysis.
Results
We found that soil organic carbon and reactive aluminum and iron species were stronger predictors of nutrient distribution than the silt and clay content. In particular, short-range order (SRO) Al and Fe mineral phases were strongly correlated with the distribution of potassium and phosphorus. Preferential association of K with SRO phases likely contributed to K retention in the profile. Phosphorus sorption to SRO phases decreased the amount of available P. Contrary to generally expected geochemical behaviour, labile P was negatively related to pH. We attributed this anomalous relation to an increase in the proportion of strongly sorptive SRO Al and Fe phases at higher pH.
Conclusion
This study shows that understanding the sorptive properties of naturally-occurring SRO Al and Fe species is important to our ability to predict nutrient availability and points to the need for further investigation of the geochemical behaviour of SRO mineral phases under field conditions.