Soil Sci.Plant Nutr. 44-1, 115-123 (1998)
K.Kakuda and H.Ando
To evaluate the contribution of mass flow to the absorption
of topdressed N
by paddy rice, a pot experiment was conducted under different
rates of
water uptake at the panicle formation stage. The rate
of water uptake was
modified by using two different values of relative humidity
(RH, 75% and
95%). Labelled N was used to determine the amount of
absorbed
fertilizer-derived N in the rice plants.
The amount of ammonium N (NH4+-N) in the floodwater was
depleted
within 48 hours after topdressing (HAT) in all the treatments.
The
concentration of NH4+-N in the soil solution decreased
with depth in the
top 0.03 m of soil. N in the soil solution from 0 to
0.03 m soil depth was
almost depleted by 48 HAT. The percentage of fertilizer-derived
N recovered
by plants and the pattern of N accumulation were the
same in all the RH
treatments. However, in the course of the entire
experiment, the amount of
N absorbed through mass flow was larger in the 75% RH
treatment during the
first 48 hours. Moreover, under 75% RH conditions, the
percentage of
topdressed N in the plants that was associated with N
absorbed through mass
flow was 78% at 48 HAT and 29% at 168 HAT. These values
were significantly
higher than the previously reported values for basal
N (2.5-6.3%).
Therefore, it is concluded that the role of mass flow
in N absorption is
more significant for topdressed N than for basal N.