A field experiment was carried out to study the grain
yield and Nitrogen Use Efficiency (NUE) components of 16 inbred lines
of exotic yellow maize and their crosses. The experiment was cropped at
two nitrogen fertilizers; low (70 kg f-1) and high (140 kg
f-1), split-plot design was used. The results indicated that,
all measured traits were affected significantly by N levels, genotypes
and the interaction, except days to 50% tasseling and silking of inbred
lines which were not affected by N levels and the N x genotype interaction.
N deficiency caused delay in flowering time for male and female inflorescence,
accelerated leaf senescence, reduced total dry matter production, N-uptake
by plants, grain yield components and grain protein percentage. On the
other hand, nitrogen use efficiency for dry matter and grain production
and nitrogen harvest index were increased under limited soil N. Inbred
lines showed severe reduction for the above variables as compared to crosses.
The inbred lines 4, 9, 13 and 15 were distinguished for their superiority
in grain yield, nitrogen harvest index, harvest index, nitrogen use efficiency
for grain, N-uptake and protein percentage. Three lines, 13, 15 and 16
were the earliest in flowering and represented the highest stay green
percentage. While, the inbred lines 1, 8 and 14 were the most N-inefficient
for grain production and the lowest for grain yield. In relation to crosses,
high nitrogen harvest index, harvest index and nitrogen use efficiency
for grain were shown by the crosses (4x1), (8x7), (9x10), (9x12) and (13x15).
The crosses (4x1), (9x10), (13x15) and (13x16) surpassed the check and
recorded the highest grain yield. The highest stay green percentage was
revealed by the single cross Pioneer 3062 followed by the crosses (4x1),
(13x15) and (13x16). It is recommended to use the inbred lines; 4, 9,
13 and 15, as a N-efficient source for further studies, whereas using
the crosses; (4x1), (8x7), (9x10), (9x12) and (13x15) as N-efficient hybrids
for under N limited cultivation. Phenotypic correlation coefficients were
higher at low N compared with high application rate. High grain yield
was significantly associated with delayed leaf senescence, nitrogen harvest
index, harvest index, nitrogen use efficiency for grain and yield plant-1.
High nitrogen use efficiency for grain production correlated positively
with high yield, yield plant-1, NHI and HI. N-uptake was found
to be a function of growth rate at both levels of N fertilizer.