Dynamics of microbial biomass and soil fauna in two contrasting soils cropped to barley (Hordeum vulgare L.)

Summary This study compared the dynamics of shoots, roots, microbial biomass and faunal populations in two different soils cropped to barley. The dynamics of microbial C, protozoa, nematodes, acari, collembola, shoot and root mass were measured between July and October under barley at Ellerslie (Black Chernozem, Typic Cryoboroll) and Breton (Gray Luvisol, Typic Cryoboralf) in central Alberta. Very wet soil conditions in early July reduced the barley yield at Breton. The peak shoot mass was greater at Ellerslie (878 g m^–2) compared to Breton (582 g m^–2), but the root mass did not differ significantly between sites. Microbial C at 0–30 cm depth was greater at Ellerslie (127 g m^–2) than Breton (68 g m^–2). The average protozoa population (no. m^–2) did not differ significantly between sites. The average nematode population at 0–20 cm depth was greater at Ellerslie (5.1 × 10⁶ no. m^–2) compared to Breton (1.0 × 10⁶ no. m^–2) Acari and collembola populations at 0–10 cm depth at Ellerslie (43 × 10³ and 43 × 10² no. m^–2), respectively) were greater than at Breton (2 × 10⁴ and 9 × 10² no. m^–2) respectively). Tenday laboratory incubations of 0–10 cm soil samples from Ellerslie evolved more CO₂-C (120 g g^–1 soil) compared to samples from Breton (97 g g^–1 soil), but the CO₂-C evolution did not differ when expressed on an area basis (g m^–2) due to the greater soil bulk density at Breton. The soil from Breton respired twice as much CO₂-C when expressed as a proportion of soil C and 1.5 times as much CO₂-C when expressed as a proportion of microbial C, compared to the soil from Ellerslie. The greater CO₂-C: microbial C ratio, lower flush C:N ratio, and greater protozoa population: soil C ratio at Breton compared to Ellerslie suggest that the food web was relatively more active at Breton and was related to greater C availability and water availability at Breton.