EFFECTS OF A PREGROWTH PERIOD IN AL-FREE NUTRIENT SOLUTION ON MACRONUTRIENT COMPOSITION OF 2 UPLAND RICE CULTIVARS WITH VARIOUS AL SENSITIVITY

Effects of Al on growth and macronutrient distribution (K, P, Ca and M g) were examined in two rice (Oryza sativa L.) cultivars (BG35 and IR4 5) pregrown in a nutrient solution without Al for 21 days followed by 14 days at 0, 70, 140 or 280 muM Al (pH 4.2 +/- 0.1). Relative growth rate (RGR) of pregrown plants was significantly less hampered by Al co mpared to their controls, than RGR of plants that were not pregrown. H owever, a similar ranking of the cultivars for Al sensitivity was obta ined irrespective of pregrowth period. The more Al tolerant BG35 consi stently outyielded the Al sensitive IR45 under all Al treatments. A co mparatively high Al-retention in roots and low Al transport rate to sh oots of pregrown IR45 was the opposite of conditions in non-pregrown I R45. In BG35, uptake and transport of nutrients to the shoots were eff icient at all Al levels. In IR45, particularly the uptake and distribu tion of P and Mg were disturbed by Al. It is suggested that a pregrowt h or nursery period without Al reduces Al toxicity in both BG35 and IR 45 at least up to 280 muM Al.