The Role of Soil Organic Matter and Manures in Sustainable Nutrient Cycling - Sustainable Management of Soil Organic Matter - page 309

NtoN 2 O-producing nitrifiers and denitrifiers (Højberg et al ., 1996). The
net outcome of the possible effects of elevated CO 2 on those processes
controlling N 2 O emissions are therefore complex.
Results from field experiments (Ineson et al ., 1998; Kammann et al .,
1999) and laboratory incubations (Robinson and Conroy, 1999) have
provided the first evidence of a positive feedback between elevated
atmospheric CO 2 and greater soil-to-atmosphere N 2 O fluxes. However,
more information is necessary in order to elucidate the influence of
environmental conditions and to link N 2 O fluxes from the soil surface to
below-ground processes. The present work was designed to assess possible
interactions between elevated atmospheric CO 2 and N fertilization rates
on N 2 O fluxes, plant growth and rhizosphere denitrifier activity under
controlled conditions.

Materials and Methods

Soil cores

An arable soil was sampled at Gullane (East Lothian, Scotland, GR
484813) to a depth of 20 cm. The soil was sieved moist (< 10 mm), and
stored at 4

C before use. The soil was an imperfectly drained sandy loam
(Peffer series), characterized by 62% coarse sand; 30% fine sand; 6.06%
silt; 2.07% clay; pH (H2O) 8.15; 2.52% organic matter; 0.13% total N;
2.09

°

g of available N g −1 , and 50% water-filled pore space (WFPS) at field
capacity. Soil cores (upright section of PVC pipe, 30 cm in height, 10.2 cm
in diameter) were prepared by packing dry weight equivalents of field-moist
soil to a pre-determined bulk density of 1.3 g cm −3 . Nitrous oxide emissions
from similar soil types have been reported to be significant as WFPS
increases from 50 to < 90% (Smith et al ., 1998). Thus, pre-packed soil
cores were saturated in a modified Hoagland's nutrient solution (excluding
any source of C or N) for 16 h, and left to drain gravimetrically for 48 h
before the experiment started. The water content was maintained by
placing each soil core on an individual water table. WFPS ranged from
65 to 68

µ

± 2.2-2.9% in the first 8 cm and from 80 to 84 ± 0.8-2.8% at

lower depths.

Plant-soil microcosms

Spring barley ( Hordeum disticum L.) was grown (one plant per pot) for
25 days in microcosms maintained under controlled conditions and set up
to facilitate sequential monitoring of the soil-root atmosphere (soil-root
cores were isolated from the above-ground part of the plants).