Contribution of Régis R. Simard to phosphorus research in agroecosystems and future prospects

Abstract

In this paper we present the soil test P saturation, budget, and fractionation procedures used in R. R. Simard's laboratory. We expand that work to: (1) Mehlich-III P saturation index using a weighting factor for Fe accumulation in soils; (2) P budget including below-ground biomass; and (3) compositional data analysis of P fractions to describe changing patterns of soil P fractions that differ in their availability to plants and risk to the environment. The Mehlich III P and Al two-way classification applied to forage crops by Simard and co-workers was replaced by the P/Al ratio test for P fertilizer recommendation in Quebec. The concept was further expanded to (P/ [Al+γFe), where γ is 0 or 1 in mineral soils and 5 in organic soils. To provide a more complete picture of the P budget and risk index in agroecosystems, it would be advantageous to consider root P, despite limited data. Using compositional analysis for a closed information space or simplex, a perturbation vector describing relative increase or decrease in P pools in response to a driving variable as well as the simplicial distance between control and modified soil P simplexes showed that added P primarily influenced the most labile inorganic P fractions (resin-Pi and NaHCO3-P i) in five Quebec gleysolic soils. Changes in P patterns were more prominent in coarse-than in fine-textured soils. Soil P saturation, the P budget and proximate P analysis used by R.R. Simard support current progress on P issues. Future research should address γ as a function of soil Fe forms (hydroxide or bound to organic matter), below-ground P in the P budget, and soil P compositional patterns in response to driving variables.