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TECHNICAL REPORTS

Waste Management

Biosolids Increase Soil Aggregation and Protection of Soil Carbon Five Years after Application on a Crested Wheatgrass Pasture

^a Faculty of Land and Food Systems, Univ. of British Columbia, Vancouver, BC, V6T 1Z4 Canada
^b Agriculture and Agri-Food Canada (AAFC), Pacific Agri-Food Research Centre, Agassiz, BC, V0M 1A0 Canada
^c AAFC, Kamloops Range Research Station, Kamloops, BC, V2B 8A9 Canada
^d Research Branch, BC Ministry of Forests and Range, Kamloops, BC, V2C 2T7 Canada

^* Corresponding author (brian.wallace{at}gov.bc.ca).

Received for publication November 15, 2007. Biosolids application to rangelands and pastures recycles nutrients and organic matter back to soils. The effects of biosolids (20 and 60 dry Mg ha^–1) and N+P fertilizer on soil aggregate stability, bulk density, aeration porosity, and total C and N of stable aggregates were evaluated 4 and 5 yr after surface application to a crested wheatgrass [Agropyron cristatum (L.) Gaertn.] pasture in the southern interior of British Columbia (BC). The experiment was established in 2001 in a randomized complete block design with four replications. The 60 Mg ha^–1 biosolids treatment (Bio 60) had a greater aggregate mean weight diameter (MWD) and proportion of water-stable soil aggregates > 1 mm relative to the control and fertilizer treatments. Temporal variation in aggregate stability was attributed to seasonal variations in soil water content. Surface application of 60 Mg ha^–1 of biosolids increased C concentrations within water-stable aggregates relative to the control from 29 to 104, 24 to 79, and 12 to 38 g kg^–1 for the 2 to 6, 1 to 2, and 0.25 to 1 mm size fractions, respectively. The concentration of N within aggregates increased in similar proportions to C. Neither soil bulk density, nor aeration porosity were affected by biosolids application. Increased aggregation and the accumulation of soil C within aggregates following biosolids application creates a potential for better soil C storage, soil water retention, nutrient availability, and ultimately the overall health of semiarid perennial pastures.

Abbreviations: BC, British Columbia • AAFC, Agriculture and Agri-Food Canada • Bio-20, biosolids application at 20 dry Mg ha^–1 • Bio-60, biosolids application at 60 dry Mg ha^–1 • MWD, mean weight diameter