Screening Chinese wheat germplasm for phosphorus efficiency in calcareous soils

Twenty commonly used winter wheat genotypes collected throughout China were used in field screening for phosphorus (P)-efficient germplasm in a calcareous soil with and without fertilizer P application; the same genotypes were also evaluated for high and low P inputs in a greenhouse experiment. The overall criterion for P efficiency was the capacity to produce a relatively high yield with low P availability. Significant differences in grain yield production occurred between efficient and inefficient genotypes. Four parameters were calculated to determine which was the most useful for describing P efficiency: (1) percentage of relative yield with no applied P; (2) total P uptake; (3) P-harvest index (PHI: grain P/total P uptake); and (4) P-utilization efficiency (PUE: grain yield produced per unit of P taken up). A simple but satisfactory criterion in screening P-efficient wheat genotypes, 85% of relative grain yield at low P/high P, was recommended and proved to be more effective than the other three parameters. With this criterion, 12 out of 20 genotypes were classified as P-efficient (<= 15% yield reduction with no P applied) from both field and pot experiments. Phosphorus efficiency may have resulted from either P uptake or P-utilization efficiency. Three parameters, namely relative yield without applied P, PHI and PUE, were found to be useful, together with P uptake, in determining overall P efficiency. Successful selection for P efficiency was found to be possible at the shooting stage (but not at tillering) by comparing P uptake and P-utilization efficiency of plants at this growth stage with those of plants at maturity.