The effects of phosphorus (P) deficiency on plant symptoms, yield, and
components of yield of wheat (Triticum aestivum L. cv.
Halberd), P uptake, and the distribution of dry weight within plants of
variable P status were examined in 2 glasshouse and 5 field experiments.
Apart from stunted growth and depressed tillering, the symptoms of acute P
deficiency, most noticeable on older leaf blades, were equivocal; they were
not always observed on acutely deficient plants and were absent on moderately
deficient plants. In glasshouse experiments, the leaves of acutely deficient
plants were spindly, erect, and dark green, whereas in field experiments, the
leaves were pale green.
In acutely P-stressed plants, leaf senescence, phasic development, and
anthesis were delayed. The disorder restricted tiller development and
therefore the rate of appearance and the number of leaves per plant. It
depressed grain yield principally by reducing the number of fertile tillers.
Severe P deficiency depressed shoot growth within 15 days of sowing and
ultimately reduced plant height, root mass, and grain yield. In all
experiments, shoot yield responses to applied P increased progressively until
stem elongation (Zadoks Scale 30) and changed little thereafter. As a result,
the external requirement for P (i.e. P level required for 90% maximum
growth) increased with time during vegetative development in most experiments.
Severe P deficiency also affected the distribution of dry matter between the
roots and shoots and between the leaf blades and conducting tissues (sheaths
and stems). Both of these responses intensified with advancing plant age.
Treatment differences in P uptake in shoots also occurred early in growth and
persisted until grain maturity. The partitioning of P between roots and shoots
favoured P uptake or retention in the roots of P-deficient plants.
Under conditions of acute and moderate P stress, the resources of the wheat
plant appear to be directed towards maintaining root growth (at least
initially), limiting and delaying shoot proliferation, and maximising the leaf
: stem ratio. These regulations appear circumstantially to be adaptive
mechanisms for conserving suffiient P to ensure the survival of at least 1
weak, but fertile, tiller on each plant.
Production of Oxalic Acid as Influenced by the Application of Organic Residue and Its Effect on Phosphorus Uptake by Wheat (Triticum aestivum L.) in an Inceptisol of North India
