Nerson, H., Agricultural Research Organization, Neve Ya'ar Experimental Station, Israel
Edelstein, M., Agricultural Research Organization, Neve Ya'ar Experimental Station, Israel
Pinthus, M.J., Faculty of Agriculture, The Hebrew University of Jerusalem, Rehovot, Israel

The effects of N and P on the number of spikelets of spring wheat (Triticum aestivum L.), grown in nutrient solution, were studied under 8 h and 16 h photoperiods. The effect of P was apparent only at a high rate of N supply and the effects of N were increased significantly at a high rate of P supply. Increasing N supply increased the number of spikelets due to a promotion of the rate of spikelet initiation. It also increased the leaf-blade area and the dry matter weight of the plants at the stage of terminal spikelet initiation. These effects of N were much greater under the short photoperiod than under the long photoperiod. The practical significance of these findings for winter-grown wheat in temperate regions is pointed out. © 1990 Kluwer Academic Publishers.