Interaction of phosphate and salinity on the growth and yield of rice (Oryza sativa L)

The role of phosphorus application on growth and yield of rice under saline conditions was studied in a set of two experiments, one in nutrient and the other in soil culture. In experiment 1, the effect of inorganic phosphate (P-i) on the growth and ionic relations of four rice cultivars, varying in salt tolerance and phosphorus use efficiency, grown in nutrient solution with and without 50 mol m(-3) NaCl was measured in a 2 week trial. The growth of ail rice cultivars was affected to different degrees due to external P; in the presence of sale. External P-i concentration up to 100 mu M in the presence of NaCl caused stimulation of all growth parameters (shoot, root, tillering capacity), above this concentration P-i had an inhibitory effect. Salt-induced P toxicity was exhibited at a much lower P-i concentration (10 mu M) by the salt sensitive cultivar. Increasing the supply of phosphorus (from 1 to 100 mu M P-i) to the saline medium tended to decrease the concentrations of Na+ and Cl- in all cultivars except IR 1561. Shoot concentrations of these saline ions were much lower in the salt tolerant and moderately salt tolerant rice cultivars. Shoot P and Zn concentrations showed an increasing trend in the presence of external P-i and salt in the rooting medium but most strikingly P:Zn ratio was lower in salt tolerant and moderately salt tolerant cultivars. Significantly higher concentrations of Na+, P and Cl-, and lower concentrations of Zn, were determined in the shoots of salt sensitive cultivars when exposed to salt stress in the presence of P-i. Results were confirmed in naturally salt-affected soils of two different types (saline-sodic and saline) where paddy yield of NIAB 6 (salt tolerant) and IR 1561 (salt, sensitive) showed improvement through moderate phosphorus supply (18 kg P ha(-1)).