Understanding nutrient cycling under different land uses can improve agricultural management practices. In southwestern Saskatchewan, long-term land use as annual cropland, native grassland pasture, tame (planted) crested wheatgrass grasslands, or roadsides altered soil physical and chemical properties based on the intensity and frequency of disturbance, with cropland > roadsides > tame grassland > native grassland. The majority of significant differences were detected at the soil surface (0-7.5 cm); few significant differences below 15 cm suggested that the soils were not significantly different prior to changes in land use. Bulk density was increased in cropland soils compared with native grassland, probably from compaction from farm equipment, and in tame pastures due to their past use as croplands. Croplands also had decreased carbon and organic phosphorus (P) and increased Olsen P compared with grasslands, from crop removal and fertilizer inputs. Roadsides, an important but poorly studied land use in Saskatchewan, had increased clay and Olsen P concentrations compared with native grassland. Roadsides were disturbed during road building and remained disturbed because of runoff from adjacent fields and dust from roads. These results on soil chemical and physical properties, combined with soil microbiology information, will help to improve land management and nutrient use efficiency in soils of this region.

Thorpe, J., Wolfe, S. A. and Houston, B. 2008. Potential impacts of climate change on grazing capacity of native grasslands in the Canadian prairies. Can. J. Soil Sci. 88: 595Á609. Relationships between climate and native grassland production in the Canadian prairies were modelled and used to estimate the potential impacts of climate change on grazing capacity. Field measurements of production were related to climate variables and water balance estimates using regression analysis. Historical time series showed that year-to-year production is most closely correlated with annual actual evapotranspiration, whereas geographic patterns revealed that average production is most closely related to the annual water deficit. Climate and production estimates from the US Great Plains represent potential analogues for the Canadian prairies in the 2050s. Analysis of geographic patterns using Canadian and US data showed that production can be related to actual evapotranspiration (Model 1) or the ratio of actual to potential evapotranspiration (Model 2). The proportion of warmseason (C 4 ) grasses has a significant effect on production in these models. A third independent model (Model 3) using US production data was used for comparison. Five general circulation model (GCM) scenarios covering a range of predictions simulated warmer climates of the 2050s. The production models were used to estimate changes in grassland production. On loamy soils, Model 1 predicts increases in production whereas Models 2 and 3 predict decreases. However, all predicted changes are modest, indicating that Canadian grasslands will probably remain productive over the next 50 yr. In addition, warm-season grasses could increase, particularly on sandy soils, thus benefiting productivity.Key words: Climate change, grazing capacity, grasslands, prairies Thorpe, J., Wolfe, S. A. et Houston, B. 2008. Conse´quences potentielles du changement climatique sur la capacite´de paissance des paˆturages naturels dans les Prairies canadiennes. Can. J. Soil Sci. 88: 595Á609. Les auteurs ont mode´lise´les relations entre le climat et la production des paˆturages naturels des Prairies canadiennes puis ont estime´l'incidence e´ventuelle du changement climatique sur la capacite´de paissance. La production mesure´e sur le terrain a e´te´associe´e aux variables climatiques ainsi qu'au bilan hydrique estimatif par une analyse de re´gression. Les se´ries chronologiques re´ve`lent que la variation annuelle de la production pre´sente la meilleure corre´lation avec l'e´vapotranspiration re´elle annuelle, alors que, selon les tendances ge´ographiques, la production moyenne est davantage relie´e au de´ficit hydrique annuel. Le climat et la production estimative des Grandes Plaines des É tats-Unis pourraient servir d'analogie a`ce a`quoi ressembleront les Prairies canadiennes dans les anne´es 2050. L'analyse des tendances ge´ographiques a`partir des donne´es canadiennes et ame´ricaines indique qu'on peut associer la production a`l'e´vapotranspiration re´elle (mode`le 1) ou au ratio ...

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Differentiation of grassland/forage types and accurate estimates of their location and extent are important for understanding their ecological processes and for applying appropriate management practices. We are aiming to reveal the different spectral characteristics of six grassland/forage land covers in three ecoregions located in the Canadian Prairies, based on field data and satellite images. Three spectral indices representing productivity (Normalized Difference Vegetation Index (NDVI)), moisture content (Normalized Difference Moisture Index (NDMI)), and plant photosynthetic activity (Plant Senescence Reflectance Index (PSRI)) were used for comparison of means, comparison of coefficient of variation (CV), and analysis of variance (ANOVA). The results indicated that different grassland types show distinguishable spectral characteristics in the Moist-Mixed and Mixed Ecoregions, while it was not possible to differentiate the classes in the Fescue Ecoregion. To further investigate the within-sites and between-sites heterogeneity, we calculated the CV in a 3 × 3 window and placed them in comparative triangles to demonstrate their potential separability. Results indicated that the triangles based on the CV offered greater class separability in the Fescue Ecoregion and in the Mixed Ecoregion.

The nature of the soil, the influence of previous natural grassland, ley, fallow or cultivation, and the weather conditions before and after planting are shown to affect the yield of wheat, and its response to fertilizers, especially nitrogen. Out of seventeen experiments over four seasons, involving nitrogen top-dressings on wheat, thirteen gave economic increases after the application of 1 cwt per acre of ammonium sulphate nitrate (A.S.N.). Such applications to the first, second or third wheat crops after Rhodes grass (Chloris gayana) ley, or to land continuously cropped for a number of years, nearly always gave an economic increase in grain yield, but on continuously cultivated land, with normal rainfall after planting, an economic return to a second cwt per acre was probable. Following a one-season fallow, economic responses to nitrogen only occurred when the pre-planting period was very wet. Yields of wheat after ley, both with and without applied nitrogen, tended to be superior to those on continuously-cropped land. Responses to phosphorus only occurred in one area, where the importance of applying both N and P, particularly to newly-ploughed grassland, was very evident. Loss of organic matter, and structural deterioration accompanied by lower efficiency in the utilization of water and nitrogen, are probably the main causes of falling yields on soils cultivated for many years. The use of grass/ legume leys is suggested as the best means of maintaining these naturally fertile soils in a highly productive state, even though the present returns from the leys themselves may be less profitable than wheat cropping.