| Abstract: | In a field trial in Northwest Mexico, the phosphorus efficiency of three advanced bread wheat lines (Triticum aestivum L.) from CIMMYT were compared with an older Mexican variety Curinda, under irrigation, on an alkaline clay soil (3.7 mg Olsen-P kg—1 soil) without (P-0) and with P-fertilisation (P-35; 35 kg P ha—1). Dry matter, P-content, P-uptake of above ground biomass and root growth (root length densities in different soil depths) were measured at different growth stages, and the net P-uptake rates per unit root length calculated. All four genotypes responded positively to P-fertilisation. The three new genotypes showed significantly higher grain yields compared with the old variety Curinda, on the average, 54% and 42% higher at P-0 and P-35, respectively. The higher grain yield was mainly due to a larger number of kernels per ear, higher thousand kernel weight as well as a higher harvest index. The old variety Curinda had the same (P-0) or greater (P-35) number of spikes m—2 than the new genotypes. In conclusion of this experiment, the three new genotypes could be classified as more P-efficient. The P-uptake at harvest averaged 35% and 24% more than the old variety Curinda at the P-0 and P-35 level, respectively. The improved P-efficiency was mainly due to a more efficient P-uptake. However, there were only small differences in P-utilisation efficiency (kg grain per kg P in shoots) between old and new varieties (8—11%). The differences in the root systems were more decisive in the P-0 treatment than with P-fertilisation. At low P, the improved P-uptake per ha of the advanced lines was due to a higher root length density especially after flowering, while at high P, a higher P-influx rate per unit root length played a more important role than the root length density. The superiority of the new genotypes at both P levels is obviously due to the good adaptation of their root system (root length density, uptake rate per unit root) to variable P availability in soil. |
