Cultivar and N Fertilizer Rate Affect Yield and N use Efficiency in Irrigated Durum Wheat

Optimizing N management and using cultivars with high N use efficiency (NUE) are important for durum wheat ( Triticum durum Desf.) producers in irrigated desert production systems. A field experiment with six durum wheat cultivars was conducted with five or six levels of N treatment for two growing seasons (2010–2011 and 2011–2012) to determine NUE and yield of durum wheat cultivars under irrigated desert conditions. Recovery efficiency of N fertilizer was very high, ranging from 63 to 79%. Durum wheat cultivars differed in grain N concentration (GNC) in both seasons. In the 2011 to 2012 growing season, cultivars differed in grain yield, agronomic efficiency (AE), NUE, and N harvest index (NHI). The N fertilizer rate had a highly significant, positive effect on nearly all variables in both seasons. As the N fertilizer rate increased, grain yield, GNC, and total N uptake increased and then plateaued, while AE and N utilization efficiency (NUtE) decreased linearly. Nitrogen uptake efficiency (NUpE) and NUE decreased as a power function with increased N fertilizer rates. Durum wheat NUE was more closely related to NUpE than NUtE. The N harvest index responded in a quadratic manner to N rate in both years. In summary, although there was variation in grain yield and NUE among durum wheat cultivars, N fertilizer effects were much more significant than cultivar effects. This indicates that grower decisions on optimal N rate will have more impact than cultivar selection.