Tuesday, 8 November 2005
12

Carbon Content of the Alberta Soil Quality Benchmark Sites.

R. Jason Cathcart1, Doug Keyes2, and Jody Heinz1. (1) Alberta Agriculture, Food and Rural Development, J. G. O'Donoghue Building, #206, 7000 - 113 Street, Edmonton, AB T6H 5T6, Canada, (2) Pro Soil Investigations Inc., Box 1, Site 1, RR1, Leduc, AB T9E 2X1, Canada

Organic carbon (OC) content measured from the Alberta Environmentally Sustainable Agriculture (AESA) Soil Quality Resource Monitoring Program will be presented. This program consists of 42 sites distributed on farm-fields throughout the agricultural ecoregions of Alberta. At each site, upper, mid and lower slope positions were sampled at two depths (15 and 30 cm) to evaluate the influence of both ecoregion and topography. The sites have been monitored since 1998, and provide a unique opportunity to examine soil OC under a broad range of soils, climate and management practices. Average carbon content was 16.6 kg m-2 (166 t ha-1), but ranged from 8.3 kg m-2 (83 t ha-1) in the Mixed Grasslands to 25.1 kg m-2 (251 t ha-1) in the Peace Lowlands. There were no significant differences between slope positions although, for most ecoregions, there was a trend toward increased OC in the lower slope position. Seven years of data collection is a short time period relative to organic matter turnover, thus significant changes in OC were not necessarily expected. Results do indicate a trend toward increasing OC within many ecoregions and slope positions. An average increase of 0.88 t ha-1 of soil OC was observed after eliminating 12 of the total 126 profiles that were considered to be non-representative. The greatest increases appeared in the southern grassland regions and the Peace region. Although these trends were not statistically significant, there were several significant differences in OC between years. These rates of increase are greater than would be expected based on other research/modeling in western Canada. The reasons for the apparent changes could not be established based on the available information for these sites, although tillage and cropping practices did not appear to be a factor. There was some indication that increases in soil carbon was associated with climate.

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