Response of Pearl Millet to nitrogen as affected by water deficit

In the Sahelian zone, low soil N could be as limiting as drought in pearl millet production. Although growth and crop productivity depend on several biochemical reactions in which the nitrogen metabolism plays a great role, there is little information available on how N uptake and key enzymes, nitrate reductase and glutamine synthetase, are affected by nitrogen and water interaction in millet. For this purpose, the millet variety cv. Souna III was grown in the field during the dry season under three levels of nitrogen fertilization (NO = 0.0, N1 = 17.13, and N2 = 68.50 kg N ha -1 ) and different water regimes (well-watered and water-stressed) in a split-plot experimental design. Irrigation was stopped for water-stressed plants during tillering, and the grain formation and filling phases, thereby giving rise to two water deficit cycles. A major quantity of mobilized N (79-100%) was taken up before flowering in all N treatments. Nitrogen uptake declined significantly only during the second water deficit cycle. During the first water deficit cycle, aboveground biomass was reduced and the maintenance of the N uptake resulted in increased N and nitrate concentrations. The water deficit reduced nitrate reductase activity in all treatments and the effect was greater under high N. The increase in nitrate concentration under water deficit conditions showed that the reduction in nitrate reductase activity was probably not due to limiting nitrates. Glutamine synthetase activity was higher under the low N treatments, N1 and N0, showing the absence of a stimulating effect of glutamine synthetase activity by nitrate or ammonium. These results are discussed on the basis of their effect on grain N and grain yield.