Genetic Gain in Wheat Grain Yield and Nitrogen Use Efficiency at Different Nitrogen Levels in an Irrigated Hot Environment
Izzat Sidahmed Ali Tahir, Elfadil M. E. Elbashier, Mohamed Ibrahim, Abu Sefyan I. Saad, O. Abdalla
Abstract
Improved nitrogen use-efficient cultivars could be the most economically beneficial and environmentally friendly approach to reduce pollution associated with excessive N fertilization. The performance and genetic gain in grain yield and nitrogen use efficiency (NUE) of a historical set of 12 bread wheat cultivars released for a heat-stressed environment were investigated at four N levels (0 (N 0 ), 43 (N 43 ), 86 (N 86 ), and 129 (N 129 ) kg/ha) for two seasons. Averaged across seasons, increasing N level from N 0 to N 43, N 86 , and N 129 resulted in yield increases ranging from 4−45%, 13–69%, and 34–87% at N 43, N 86 , and N 129, respectively. These yield increases were associated with increases in biomass ( r = 0.86, <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" id="M1"><mml:mrow><mml:mi>P</mml:mi><mml:mo><</mml:mo><mml:mn>0.01</mml:mn></mml:mrow></mml:math>). Regressing grain yield of cultivars released during 1960 to 2006 against the year of release showed no trend at N 0 and positive nonsignificant trends at N 43 ; . however, significant positive trends were found at N 86 and N 129 with genetic gain rates of 12.65 and 15.76 kg ha −1 year −1 , respectively. This gain was associated with progresses in harvest index (HI) at N 43 , N 86 , and N 129 but not at N 0 . On the other hand, during the period from 1960 to 1990, the genetic gain in grain yield at N 86 was 24.5 kg ha −1 year −1 . Regressing NUE against the year of release showed significant linear trends at N 86 and N 129 ( R 2 = 0.511 and R 2 = 0.477, respectively), but not at N 43 . The results indicate that breeders improved grain yield and NUE over 46 years under the heat-stressed environment of Sudan although the rate of increase in yield has been slowed down in recent years. Further improvement in NUE might require broadening the genetic diversity and simultaneous evaluation at low and high N levels.