H.Ando, K.Kakuda, M.Nakayama, and K.Yokoto
Key words: controlled-release fertlizer, N use efficinecy,
no-tillage, paddy rice, recovery percentage of basal N
Due to high the labor cost, direct seeding is being gradually
applied for crop establishment throughout Asia. Recently, the development
of the so-called, “controlled release fertilizers (CRFs)” which requires
only “one shot dose” of N, has enabled to reduce the cost of labor for
the application of topdressed N. Thus, in order to limit pollution and
cost, no-tillage direct-seeded lowland rice cultivation accompanied by
the use of CRF is being recommended. To evaluate the effects of CRFs on
the growth and yield of no-tillage direct-seeded rice, a field experiment
was carried out in the north-eastern region of Japan in 1993 and 1994.
Five N treatments were used: (1) ammonium sulfate (AS) band placement application
with seeds at the time of seeding (AS1); (2) AS broadcast application after
irrigation (AS2); (3) CRF (LP100) co-situs application at the time of seeding
(L1); (4) CRF (LPS100) co-situs application at the time of seeding (L2);
and (5) minus N (MN). The rate of basal N was 60 kg N ha-1.
Topdressed N in the AS1 and AS2 treatments was applied at 25 days before
heading at the rate of 20 kg N ha-1
. The highest yield was obtained in the L1 treatment in both years. The
number of grains per unit area was affected by the amount of N in the plants
at heading. The percentage of filled grains in the L2 treatment was the
lowest by about 15-20% among the treatments. The recovery percentages of
basal N on July 20 were about 20 to 30 % in the AS1, AS2 and L1 treatments,
and only about 14% in the L2 treatment. About 75 to 80 % of basal N was
absorbed by the plants at harvest in the L1 and L2 treatments. On the other
hand, the plants had absorbed only about 25 to 30 % of the applied basal
N in the AS1 and AS2 treatments at harvest. There was no difference in
the N-recovery percentage (based on the amount of released N) between the
L1 and L2 treatments. Nitrogen-use efficiency was not significantly different
among the treatments. However, higher N-use efficiency was obtained in
this experiment than in early studies in the tropics. The agronomic efficiency
of CRFs was higher than that of ammonium sulfate.