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 s aline conditions was studied in a set of two experiments, one in nutri ent and the other in soil culture. In experiment 1, the effect of inor ganic phosphate (P-i) on the growth and ionic relations of four rice c ultivars, varying in salt tolerance and phosphorus use efficiency, gro wn in nutrient solution with and without 50 mol m(-3) NaCl was measure d 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 stimu lation of all growth parameters (shoot, root, tillering capacity), abo ve this concentration P-i had an inhibitory effect. Salt-induced P tox icity 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 concentra tions of Na+ and Cl- in all cultivars except IR 1561. Shoot concentrat ions of these saline ions were much lower in the salt tolerant and mod erately salt tolerant rice cultivars. Shoot P and Zn concentrations sh owed an increasing trend in the presence of external P-i and salt in t he rooting medium but most strikingly P:Zn ratio was lower in salt tol erant and moderately salt tolerant cultivars. Significantly higher con centrations of Na+, P and Cl-, and lower concentrations of Zn, were de termined in the shoots of salt sensitive cultivars when exposed to sal t stress in the presence of P-i. Results were confirmed in naturally s alt-affected soils of two different types (saline-sodic and saline) wh ere paddy yield of NIAB 6 (salt tolerant) and IR 1561 (salt, sensitive ) showed improvement through moderate phosphorus supply (18 kg P ha(-1 )).