DUGi

Compositional analysis of phosphorus pools in Canadian Mollisols

http://dugi.udg.edu/item/http:@@@@hdl.handle.net@@2072@@273643

During cultivation, the internal phosphorus cycle of Mollisols (Chernozems) of the CanadianPrairies is perturbed by crop sequences including wheat phases, tillage practices, and regularapplications of fertilizers. To monitor these changes, a proximate sequential phosphorus (P)fractionation procedure was developed by Hedley et al. (1982) to extract inorganic and organic Pfractions as very labile (resin-P), labile (NaHCO3-P), slowly available (NaOH-P), and very slowlyavailable (HCl-P) pools. Models used so far to monitor P pools do not address the interactivebehaviour of P fractions constrained to a closed compositional space. Compositional data analysisusing isometric log ratio (ilr) coordinates is appropriate for modelling the interactive P pools usingsequential binary partitions of P pools. Our objective was to model changes of P pools in Mollisolsin response to management and time using ilr coordinates. We used a dataset with treatments andanother where a Mollisol was analyzed at time zero and 4, 65, and 90 yr after sod breakup. Seven Pfractions were assigned to P reactivity groups to compute six ilr coordinates. The ilr2 contrastinginorganic (geochemical) and organic (biological) P pools and ilr4 between the most readily availableand less P bioavailable pools were the most sensitive to crop sequence and fertilization. Usingcomposition at time zero as reference, the Aitchison distance reached a plateau after the 4th year inthe Bm horizon compared to continuous change in the Ah horizon. Time changed the P balance ofcultivated Mollisols primarily in the inorganic vs. organic P pools. The risks of yield loss andenvironmental damage can be minimized using soil tests that quantify the rapidly bioavailableinorganic P pools and crop management strategies that promote biological P pools.

Universitat de Girona. Departament d’Informàtica i Matemàtica Aplicada