A field experiment was conducted in the dry season at Los Banos, Phili
ppines, to assess the differences in grain yield and N utilization of
10 medium-duration (119+/-4 days after seeding [DAS]) genotypes and 10
long-duration (130+/-4 DAS) ones with varying acquisition and usage o
f soil and fertilizer N. Significant differences among genotypes were
observed in grain yield and N uptake, efficiency and partitioning para
meters (physiological N use efficiency [PNUE], agronomic N use efficie
ncy [ANUE], apparent recovery [AR], partial factor productivity of app
lied N [PFPN], N productivity index [NPI], and N harvest index [NHI]),
The N-efficient genotypes that produced high grain yield at both low
and high levels of N were IR54790-B-B-38, BG380-2, BG90-2 (medium-dura
tion), and IR3932-182-2-3-3-2, IR54853-B-B-318, and IR29723-88-2-3-3 (
long-duration). Inefficient genotypes that produced low yields at low
N levels but responded well to N application were IR58125-B-B-42, IR49
457-33-1-2-2-2, and BG34-8 (medium-duration), and IR8192-200-3-3-1-1,
IR21848-65-3-2-2, and PR106 (long-duration). IR20 (medium) and Palawan
(long-duration) were N-inferior genotypes giving low yields at both l
ow and high N levels. Increase in grain yield was highly correlated wi
th N uptake (r=0.75**). The grain yield-N uptake relationship for ind
ividual genotypes indicated significant differences in slope and in th
e yield obtained with soil N (GY(o)). Differences in GYo were due to g
enotypic variation in N uptake and efficiency of use. NHI was related
to both N uptake and use efficiency. NPI, which integrated both GYo an
d PNUE, provided a better ranking of genotypes, The performance of eff
icient and inefficient genotypes over a range of soil and fertilizer N
supply was consistent over three seasons of trials. (C) 1998 Elsevier
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