Vp. Aneja et al., NITROGEN-OXIDE FLUX FROM AN AGRICULTURAL SOIL DURING WINTER FALLOW INTHE UPPER COASTAL-PLAIN OF NORTH-CAROLINA, USA, Journal of the Air & Waste Management Association [1995], 47(7), 1997, pp. 800-805
Incorporation of the remaining crop residue, including the root system
, of grain (soybean and corn) and fiber (cotton) crops into the soil f
ollowing harvest is a common agricultural practice. The crop residue r
epresents a substantial portion of nitrogen initially applied as ferti
lizer, and thus is a potential source of nitrogen for NO emissions dur
ing the winter fallow period. Fluxes of NO and NO2 were measured from
fallow fields from February 7 to March 23, 1994, using a dynamic chamb
er technique (ambient air as the carrier gas). Average NO flux rates,
as a function of previous crop residue, were 9.2 (range -4.2 to 76) ng
-N m(-2) s(-1) for soybean, 6.1 (range -11.7 to 110) ng-N m(-2) s(-1)
for cotton, and 4.7 (range -0.2 to 40) ng-N m(-2) s(-1) for corn. Maxi
mum NO fluxes were observed in midmorning when soil temperatures were
lowest. Minimum NO flux occurred after mid-afternoon when soil tempera
ture reached a maximum. The decrease in NO flux with increase in soil
temperature (5 cm depth) reflected the existence of a NO compensation
concentration (i.e., the rate for the NO consumption reactions continu
ed to increase with increase in temperature). NO2 deposition was calcu
lated for 92% of the data points, with no trend in deposition between
the three fields and their corresponding crop residue. These results i
ndicate that significant fluxes of NO are generated from fallow agricu
ltural fields following incorporation of the residue from the previous
crop.