Leclerc, M. L., Nolin, M. C., Cluis, D. and Simard, R. R. 2001. Grouping soils of the Montreal Lowlands (Quebec) according to fertility and P sorption and desorption characteristics. Can. J. Soil Sci. 81: 71-83. Soil tests P (STP) developed to estimate P fertilizer needs and designed to produce optimal economic crop yields, are often not well suited to assess potential environmental impact of fertilization practices. The objective of this study was to develop interpretative soil groupings of the Montreal Lowlands area (MLA) based on soil physico-chemical properties and on soil P sorption and desorption characteristics. Soil P sorption and desorption characteristics together with STP may help in evaluating potential risks of soil P addition. Sixty-six soil types (phases of soil series based on surface texture) were selected as representative soils of the study area. Twenty-seven soil properties were used, including Mehlich-3 extractable P and Al, ammonium-oxalate extractable P, Fe and Al, P sorption index (Psi) and Bray-2 extractable P (BR2P). Multivariate analysis was applied to generate clusters and interpret soil groupings. Principal components analysis yielded two components related: (1) to soil inherent fertility (texture) and (2) to P sorption capacity and desorption intensity. The Ward's clustering method was then applied to the first two component scores. Five soil fertility groups were obtained. Multiple discriminant analysis proposed a classification model using a small subset of variables. Five variables were selected among the soil survey characteristics for discriminating soil groups: clay content, pH measurement in water, cation exchange capacity, BR2P and ammonium-acetate extractable Mg. Adding Psi in the model improved the classification correctness. The results of this study indicate that physico-chemical properties of the surface layer used together with soil P sorptiondesorption characteristics contributed to the development of an interpretative grouping that may also be useful to assess vulnerability to water contamination by P. Les indicateurs du contenu en P disponible dans le sol, utilisés pour évaluer les besoins en fertilisants P et designés pour produire un rendement optimal des cultures, sont souvent mal adaptés pour évaluer l'impact environnemental potentiel des pratiques de fertilisation. L'objectif de cette étude était de développer un groupement interprétatif de sols de la plaine de Montréal basé sur les caractéristiques reliées au P ainsi que sur les propriétés physico-chimiques de ces sols. Les caractéristiques de sorption et de désorption du P ajoutées aux indicateurs du contenu en P disponible pourraient aider à évaluer le risque potentiel de l'ajout de P dans le sol. Soixante-six types de sols (phases de séries de sols basées sur la texture de surface) ont été sélectionnés pour représenter les sols de la région étudiée. Vingt-sept indicateurs de sol été utilisés tels que les éléments P et Al extractibles au Mehlich-3, les éléments P, Fe et Al extraits à l'oxalate d'ammonium, un...

The indicator of risk of water contamination by phosphorus (IROWC_P) is designed to estimate where the risk of water P contamination by agriculture is high, and how this risk is changing over time based on the five-year period of data Census frequency. Firstly developed for the province of Quebec (2000), this paper presents an improved version of IROWC_P (intended to be released in 2008), which will be extended to all watersheds and Soil Landscape of Canada (SLC) polygons (scale 1:1, 000, 000) with more than 5% of agriculture. There are three objectives: (i) create a soil phosphorus saturation database for dominant and subdominant soil series of SLC polygons – the soil P saturation values are estimated by the ratio of soil test P to soil P sorption capacity; (ii) calculate an annual P balance considering crop residue P, manure P, and inorganic fertilizer P – agricultural and manure management practices will also be considered; and (iii) develop a transport-hydrology component including P transport estimation by runoff mechanisms (water balance factor, topographic index) and soil erosion, and the area connectivity to water (artificial drainage, soil macropores, and surface water bodies).

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An indicator of risk of water contamination by phosphorus (IROWC-P) was developed to estimate the risk of phosphorus (P) contamination in water by agriculture, and to evaluate how this risk changes over time based on the census data obtained every 5 yr. For the province of Quebec, IROWC-P is calculated with census data from 1981, 1986, 1991, 1996 and 2001. In 2001, 85% of the Soil Landscapes of Canada (SLC) agricultural polygons of Quebec were in the low and moderate risk classes and the remaining 15% in the high risk class. Although agricultural production statistics show marked changes from 1981 to 2001 in livestock herd composition, area under cultivation, agricultural land use and use of inorganic phosphorus fertilizer and animal manure, no trend was observed in the estimated risk over the same period. Increased risk of P transport from agricultural fields to water is expected when agricultural soils are rich in P or have excess P relative to crop needs and have a high potential for soil erosion and surface runoff. Key words: Risk indicator, water contamination, phosphorus, soil landscapes of Canada, agriculture