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The effects of a single biosolids application on soil physical properties in three forage production systems in the southern interior of British Columbia Wallace, Brian Mark

Abstract

The Greater Vancouver Regional District applies about 15,000 dry tonnes of biosolids per year to various types of land in British Columbia (BC) in an effort to divert biosolids from landfilling, incineration, and ocean disposal. The effects of biosolids (20, and 60 Mg ha⁻¹) and chemical fertilizer on aggregate stability, bulk density, aeration porosity, total C and N of stable aggregates, and the hydrolysis of fluorescein diacetate (FDA) in aggregates> 2 mm were investigated five years after soil application in three common forage production systems (crested wheatgrass = CW, native range = NR, and irrigated alfalfa = IA) in the southern interior of BC. At each of the three sites, the experiment was laid out in 2001 in a randomized block design with four treatments replicated over four blocks. Soil samples were collected during spring, summer, and fall 2005 and 2006. At the CW site, biosolids at 60 Mg ha⁻¹ increased the stability and proportion of soil aggregates> 1 mm, the concentration of C and N in aggregates, and the hydrolysis of FDA. On the NR site, there were no differences in the mean weight diameter (MWD) or the proportion of stable aggregates> 1 mm from either biosolids rates, yet together the biosolids treatments were greater from the control or fertilizer treatments during every sample period in 2006. Biosolids applied at 20 Mg ha⁻¹ significantly increased total C and N of stable aggregates and reduced bulk density relative to all other treatments. At the IA site, biosolids applied at 60 Mg ha⁻¹ decreased bulk density in 2005 and 2006, relative to the control and the fertilizer treatment decreased aeration porosity and the concentration of C in aggregates. Our data showed that, land applied biosolids to these common forage production systems in the southern interior of BC enhanced aggregate stability and total C of stable aggregates. The majority of improvements to soil properties at the CW and IA sites came from biosolids applied at 60 Mg ha⁻¹, while the greatest improvements to soil properties at the NR site were from the 20 Mg ha⁻¹ biosolids treatment. This is thought to be due to greater site productivity (above and below ground) from the 60 Mg ha⁻¹ treatment at the CW and IA sites, as compared to the NR site where the 20 Mg ha⁻¹ biosolids treatment decreased bulk density and increased the concentration of C and N among stable aggregates, relative to all other treatments.

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