Nitrogen use efficiency and nitrogen fertilizer recovery of durum wheat genotypes as affected by interspecific competition.

A better understanding of the genotype response to N fertilization under weed competition is necessary to identify varieties that exhibit high N use efficiency even when weeds compete for available N. Such varieties may be more suitable for low input or organic systems. This study assessed the variations in nitrogen use efficiency (NUE) (and its components) and the recovery of 15N-labeled fertilizer in three durum wheat (Triticum durum Desf.) genotypes (one landrace and two varieties that differ in terms of plant growth, grain yield potential, and adaptability to stressful environments) grown in the presence or absence of interspecific competition and varying soil N availability (0 or 80 kg N ha−1 fertilization). The results showed that wheat genotypes had different grain yield potentials and the yields were similar when plants were grown in conditions of low N availability and in presence of interspecific competition. Differences among genotypes in N uptake efficiency were very small, and the low NUE value observed for the landrace seemed to be due to its reduced ability to use absorbed N for increasing grain yield compared with the two varieties. Furthermore, the genotypes showed different competitive abilities against competitor, and seemed to depend on the genotypes'' ability to reduce resource availability (N) for their competitors rather than on their ability to tolerate a reduction in contested resources due to competitors.