Shoot, root, soil and microbial nitrogen dynamics in two contrasting soils cropped to barley (Hordeum vulgareL.)

摘要

Dynamics of barley N, mineral N, and organic N were compared at Ellerslie (Black Chernozem, Typic Cryoboroll) and Breton (Gray Luvisol, Typic Cryoboralf) in central Alberta, using15N-urea. On average, shoot N and shoot15N recoveries at Ellerslie (14.1 g m−2, 36) were greater than at Breton (4.5 g m−2, 17). Root N (g m−2) did not significantly differ between sites (0–30 cm) but root15N recovery was greater at Breton (3.4) than Ellerslie (1.8). Low levels of shoot N and shoot15N at Breton were partly due to very wet soil conditions in July, which resulted in premature shoot senescence and low plant N uptake. Although the total15N recoveries from the system (to 30 cm depth) at Ellerslie (63) and Breton (56) were similar, soil15N was greater at Breton (35) than at Ellerslie (26). There were no differences in mineral N between sites but the average15N recovery in the mineral-N pool was significantly greater at Ellerslie (3.3) than at Breton (1.6). There was no difference in15N recovery in the microbial biomass (∼3) between sites, although non-microbial organic15N was greater at Breton (31 ) than at Ellerslie (20). The two soils showed differences in the relative size of kinetically active N pools and in relative mineralization rates. Microbial N (0–30 cm) was greater at Ellerslie (13.3 g m−2) than at Breton (9.9 g m−2), but total microbial N made up a larger proportion of total soil N at Breton (1.6) than at Ellerslie (0.9). In the 0–10 cm interval, microbial N was 1.7-fold greater and non-microbial active N was 3-fold greater at Breton compared to Ellerslie, when expressed as a proportion of total soil N. Net N mineralization in a 10-day laboratory incubation was 1.4-fold greater in the Black Chernozem (0–10 cm interval) from Ellerslie, compared to the Gray Luvisol from Breton, when expressed per gram of soil. Net N mineralization in the soil from Breton was double that of the soil from Ellerslie, when expressed as a proportion of soil N. Although soil N (g m−2) was 2.5-fold greater at Ellerslie compared to Breton, it was cycled m