A. Tirolpadre et al., GRAIN-YIELD PERFORMANCE OF RICE GENOTYPES AT SUBOPTIMAL LEVELS OF SOIL N AS AFFECTED BY N UPTAKE AND UTILIZATION EFFICIENCY, Field crops research, 46(1-3), 1996, pp. 127-143
Field screening trials were conducted in two dry seasons to assess var
iability in grain yield, N uptake and N utilization for 180 rice genot
ypes, mostly lowland indica improved varieties or elite breeding lines
of different growth durations [60 each of early (100-110 days), mediu
m (111-119 days) and late (120-135 days)], without the addition of N f
ertilizer and to identify genotypes with the potential to produce high
yields at suboptimal N levels through efficient uptake and/or utiliza
tion of N. Available soil N was lower in year 2 (20 kg ha(-1)) than in
year 1 (64 kg ha(-1)). In both years significant differences in grain
yield, N uptake and N-utilization efficiency (NUE) were observed amon
g genotypes within each growth-duration group. Genotypes varied in the
ir response to change in available soil N. The average increase in gra
in yield for each kilogram increase in N uptake was 61.9 kg in year 1
and 82.7 kg in year 2. However, some genotypes absorbed similar amount
s of N but produced different grain yields and/or total dry matter. So
me genotypes with similar harvest index exhibited significantly differ
ent NUEs - e.g., IR50363-61-1-2-2 (NUE=64.4 in year 1 and 71.9 in year
2) and IR51009-155-2-3-3 (55.3 and 60.8) in the early-duration group;
BG380-2 (70 and 78.8) and IR50391-100-2-3-3-2 (56.3 and 58.9) in the
medium; and IR27325-63-2-2 (69.7 and 69.8) and BR51-46-1-Cl (57.9 and
60.5) in the late. Those with higher NUE had lower percentage straw N
at maturity. Grain N concentration also affected NUE, but the coeffici
ent of variation in percentage grain N among genotypes was less than t
hat of percentage straw N. The relative performance of genotypes in te
rms of NUE was more consistent than plant N uptake, based on rank corr
elations between the two trials. High N uptake and NUE were observed i
n IR13429-150-3-2-1-2 (NUE 65.4, N uptake 9.1 g m(-1)) in the early-du
ration group, IR44 (NUE 67.2, N uptake 8.3 g m(-2)) in the medium-dura
tion group and IR39323-182-2-3-3-2 (NUE 64.8, N uptake 9.3 g m(-2)) in
the late-duration group. The study identified genotypes which may pos
sess promising traits for improved N uptake and utilization efficiency
. Further studies are needed to elucidate the mechanisms involved in h
igh N uptake and N-use efficiency.