Plant tests for diagnosing phosphorus deficiency in barley (Hordeum vulgare L.)

Six field experiments were conducted in the Murraylands and Mid North regions of South Australia between 1986 and 1988 to develop plant tests for diagnosing the phosphorus status of barley. The effects of applied phosphorus level on total phosphorus concentrations in youngest emerged leaf blades or whole shoots, and on shoot yield, were examined and critical ranges were established during vegetative growth. Experiments were conducted on a range of soil phosphorus levels with several methods of phosphorus placement and 2 barley cultivars. During early tillering, shoot yield and phosphorus concentrations in youngest emerged leaf blades and whole shoots were increased more by drilling phosphorus fertiliser with the seed (banded) than by spreading the same phosphorus rate over the soil surface and partially incorporating the fertiliser while sowing (broadcast). However, these methods of phosphorus placement did not affect diagnostic relationships between relative shoot yield and phosphorus concentrations in youngest emerged leaf blades and, as a result, critical total phosphorus concentrations were similar for both methods of applying phosphorus fertiliser. Estimated critical total phosphorus concentrations for both Schooner and Galleon barley were similar at each sampling time when allowances were made for minor differences in growth stages between the cultivars; even though phosphorus concentrations in youngest emerged leaf blades and whole shoots were higher in Schooner than in Galleon at adequate phosphorus supply. Between Zadoks scale 13.5 and 16.5 there was a linear decline in critical total phosphorus concentration in youngest emerged leaf blades with increasing plant age. A more variable, but steeper, decline was found for critical total phosphorus concentration in whole shoots. Critical ranges are proposed for total phosphorus concentrations in youngest emerged leaf blades and whole shoots of barley. The decline in critical total phosphorus concentration in youngest emerged leaf blades with advancing plant age was mainly caused by a higher functional requirement for phosphorus at early stages of growth and by increasing dry weight, cellulose and lignin content of youngest emerged leaf blades as plants age. Changes in the spatial distribution of applied phosphorus in relation to root growth did not seem to be important.