YIELD-INDEPENDENT VARIATION IN GRAIN NITROGEN AND PHOSPHORUS CONCENTRATION AMONG ETHIOPIAN WHEATS

New semidwarf wheat (Triticum aestivum L.) cultivars and new land mana gement practices for Vertisols are being introduced in Ethiopia, Our o bjectives were to (i) determine the variation of N and P content and c oncentration in the grain and whether these are related to gain yield, (ii) test cultivar response to different fertility levels, and (iii) assess component traits of N and P yield, Five bread wheat cultivars a nd three durum wheat (Triticum durum Desf.) cultivars were sown in Exp . 1 at three locations in Ethiopia on two dates. In Exp. 2, seven of t hese cultivars were grown on a P-deficient soil at four N levels (0, 2 0.5, 41, 61.5 kg N ha(-1)) and four P levels (0, 10, 20, 30 kg P ha(-1 )); in Exp. 3, two cultivars were grown all possible combinations of t he same four N and P levels. Grain yields did not differ among cultiva rs, but significant variations were found for total shoot N and P, gra in N and P yield, and grain N and P concentration. Cultivar difference s in these traits were fairly consistent across the treatments and wer e corroborated by Exp. 3. The N and P concentrations in the grain were not related to grain yield (r = 0.36 NS for N; r = 0.28 NS for P). Th ere was a positive association between grain N and P concentrations in Exp. 1 (r = 0.66; P = 0.07) and in Exp. 2 (r = 0.92; P < 0.01), The N and P grain yields were related to total shoot N and P at maturity (r = 0.99; P < 0.001), However, postanthesis accumulation of N was more closely related to postanthesis dry matter accumulation (r = 0.84; P < 0.05) than to the postanthesis accumulation of P (r = 0.56 NS). Total shoot P varied by as much as 50%. Thus, cultivar choice is an importa nt factor determining removal of P from the soil.