K.Kakuda, H.Ando and T.Konno
Soil Sci.Plant Nutr. 46-3, 601-610 (2000)
At the panicle formation stage, denitrification
N loss in the rhizosphere soil was investigated in a pot experiment.
A solution of ammonium-15N was injected with a syringe at a soil depth
of 50 mm to distinguish the N losses
between the surface and the rhizosphere soil. Denitrification
process in the pots with plants ((+)Plant) was compared with that in pots
where plants were cut off at the base of the culm ((-)Plant) to evaluate
the effect of plant growth on the denitrification N loss. About 50% of
the applied 15N was absorbed by the plants during the first 2 days after
fertilizer application (DAF) in the (+)Plant treatment. In the (-)Plant
treatment, no 15N absorbed by the plants after plant cutting. The amount
of exchangeable NH4+-15N in the 1st soil layer (0-20 mm) was negligible
throughout the experimental period in both treatments. The amount of immobilized
15N in the (+)Plant treatment was larger than that in the (-)Plant treatment
until 4 DAF. These results indicated that plant growth enhanced biological
N fixation in soil during the first 4 DAF. The amount of denitrified 15N
estimated in the
(-)Plant treatment (62% of applied N at 2 DAF and 21%
at 4 DAF) was larger than that in the (+)Plant treatment (2.1% at 2 DAF
and 3.5% at 4 DAF). The rate of suppression of the denitrification N loss
(RSDN) by plants was 57%
at 2 DAF and 17% at 4 DAF. The higher RSDN at 2 DAF in
this experiment was mainly due to differences between the two treatments
in the amounts of 15N recovered by the plants and immobilized in soil.
These results suggest that N absorption by the plants and N immobilization
in soil reduced the denitrification N loss in the rhizosphere soil.