DYNAMICS OF MICROBIAL BIOMASS AND FAUNAL POPULATIONS IN LONG-TERM PLOTS ON A GRAY LUVISOL

Abstract

The dynamics of microbial biomass, nematode and microarthropod populations were studied in oat (Avena sativa L.) and second-year alfalfa (Medicago sativa L.) plots of a 5-yr rotation at Breton, Alberta. Plots were sampled at monthly intervals between July and October 1984. First cut of alfalfa was taken in early July. On average shoot biomass was higher in the oat plot (691 g m−2) than in the alfalfa plot (583 g m−2); root biomass (oat 263 g m−2, alfalfa 483 g m−2) was lower than shoot mass. The average microbial biomass (chloroform fumigation technique) in the surface soil (0–15 cm) was significantly greater (P < 0.05) in the oat plot (62 g m−2) than in the alfalfa plot (43 g m−2). Average nematode population over the 4-mo period was significantly greater (P < 0.05) in the oat plot (4.1 × 106 ind. m−2) than in the alfalfa plot (2.8 × 106 ind. m−2). Nematode numbers were significantly correlated with shoot production (r = 0.97*) in the oat plot but not in the alfalfa plot. Microarthropod populations were higher (P < 0.05), on average, in the oat plot (81 000 ind. m−2) than in the alfalfa plot (48 000 ind. m−2). Total microarthropod numbers were highly correlated with soil moisture in both plots (alfalfa, r = 0.82, P < 0.001; oat, r = 0.81, P < 0.001). Higher activity of the components in the oat relative to the alfalfa system suggests that significant biological differences between plots have arisen in less than 3 yr in response to differences in crops within the rotation. In addition, microbial and faunal populations differed in their responses to changes in the soil environment. Key words: Nematode, mite, collembola, fumigation, long-term rotation