Effects of long-term and recently imposed tillage on the concentration and composition of amino sugars in a clay loam soil in Ontario, Canada

Tillage disturbance influences soil microorganisms and consequently the production and decomposition of microbial residues such as amino sugars. However, our understanding is still limited with respect to the changes in amino sugars which occur in soil after tillage operations. In this study, changes in amino sugars in a clay loam soil (mesic Typic Argiaquoll) in Ontario, Canada were tracked in long-term (29 years) no-tillage (NT), long-term conventional moldboard plow tillage (MP), and long-term bluegrass (Poa pratensis L.) sod (BG) as well as when long-term (13 years) NT was converted to MP, long-term MP was converted to NT, and long-term BG was converted to MP. Our objective was to determine if the quantity of amino sugars in the soil as well as their composition (i.e. whether they originate from bacterial or fungal residues) would respond to changes in tillage practices. We also wanted to evaluate the effects of converting from grassland to arable cropping (corn and soybean) on the amino sugar composition of soils. Soil samples were collected at depths of 0–5, 5–10, and 10–20 cm after 1 (1997), 6 (2002), 11 (2007), and 16 (2012) years following tillage conversion. Concentrations of amino sugars were much greater under long-term BG than under both long-term NT and MP treatments. In the 0–5 cm depth, long-term NT significantly increased total amino sugars and fungal-derived glucosamine (GluN) by 18 and 25%, respectively, compared with long-term MP whereas long-term NT had 26% lower MurA concentrations than long-term CT. Concentrations of total amino sugars in the 0–5 cm depth were reduced significantly within the first year after conversion of long-term NT and BG to MP, due primarily to decreases in the GluN concentrations. On the other hand, concentrations of amino sugars in soil accumulated gradually after conversion of long-term MP to NT. The results confirmed our hypothesis that loss of soil amino sugars is rapid and substantial when MP is initiated after NT and BG, while their recovery is gradual when NT is initiated after MP.