Phosphorus nutrition of spring wheat (Triticum aestivum L.). 3.Effects of plant nitrogen status and genotype on the calibration of plant tests for diagnosing phosphorus deficiency

摘要

The influence of plant nitrogen (N) status and plant genotype on plant test criteria for diagnosing phosphorus (P) deficiency in wheat was examined in 2 glasshouse experiments.nnCriteria for both total and labile P in leaf blades of standard physiological age are, to only a minor extent, affected by variations in N supply and by genotypic diversitynnInteractions between N and P supply had marked and complex effects on shoot and root yield, P and N uptake in shoots and concentrations in leaf blades, and on the distribution of P and P fractions within wheat shoots. Thus, whilst the external P requirement (i.e. P level required for 90% maximum shoot yield) more than doubled as N supply was raised, variations in N supply had only minor effects on internalP requirement (i.e. the tissue P concentration required for 90% maximum shoot yield). On the other hand, the external P requirement for root yield varied markedly with plant age and N supply.nnN deficiency increased total P concentrations in leaf blades at all P levels, primarily by increasing the concentration of the labile P fraction. Also, N concentrations increased to adequate levels in the shoots of P-deficient plants but only at the 2 lower levels of applied N.nnPlant N status also affected the shape of diagnostic relationships between relative shoot yield and P concentrations in young and mature leaf blades by constricting P concentration in the adequate-luxury zone and increasing the slope of the relationship in the zone of deficiency.nnWhilst the asymptotic grain yield and external requirement for P for the tall cultivar (Halberd) was substantially less than for the semi-dwarf cultivars (Condor and Durati), consistent P cultivar interactions on shoot yield and P uptake during vegetative growth, were largely absent. For leaf blade classes examined, the shape of the diagnostic relationship for total and labile P was essentially similar for each cultivar. As a result, differences in estimated critical P concentrations for total and labile P between the cultivars for leaf blades during vegetative growth, or criteria for grain, glumes, and straw at maturity, were relatively small.