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Efficient use of nitrogen for crop production in low input subsistence farming might increase yields, reduce cost and risk in case of crop failure. The objectives were (i) to assess genotypic and environmental variation for N use traits and (ii) to determine relationships among N use traits and between N use and agronomic traits in barleys adapted to low input tropical highlands. Twenty-six barley genotypes were tested in 1998 and 1999 in a factorial combination of two levels of N (0 or 11.5 g m−2) and P (0 or 2 g m−2) on a Eutric Nitosol at Holetta, Ethiopia. Grain yield was reduced by 75% (312 vs. 77 m−2) in 1998 and 84% (295 vs. 48 g m−2) in 1999 due to lack of N and P fertilizer. Grain N concentration was significantly lower in 1999 than in 1998. N application increased N concentrations and N yields of grain and straw, and N harvest index. Genotype effects were significant for grain N concentration, grain and straw N yields, N harvest index, and N uptake and N use efficiencies. Grain yield was correlated positively with N efficiency traits, N yields, and N harvest index but negatively with grain N concentration. Grain N concentration was correlated negatively with N use and N utilization efficiencies but was not correlated with N uptake efficiency. Nitrogen uptake efficiency was more important than N utilization efficiency in determining N use efficiency and grain yield. Of the highest yielding genotypes, lines 1829-32 and 1829-40 were high in tissue N concentration and the best in N and dry matter accumulation and line 3369-19 was low in tissue N concentration but the best in internal N utilization. The results suggest that large N uptake would raise grain yield independent of grain N concentration but uncoupling of the inverse association between grain N concentration and N utilization efficiency will be challenging. Nonetheless, the low negative correlation between grain yield and grain N concentration and the larger role of N uptake efficiency than N utilization efficiency for grain yield may allow the selection of lines that integrate high yield with high grain protein concentration. Progress in N use efficiency and grain yield may be achieved by selecting lines that integrate the uniquely high N uptake of lines such as 1829-40 with the high internal N efficiency of lines such as 3369-19, but then grain N concentration may be reduced. High yielding barley genotypes such as 3369-19 that maintain low tissue N concentration may offer productivity advantages in this and similar low input cropping systems. |
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