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 Mg) were examined in two rice (Oryza sativa L.) cultivars (BG35 and IR45) 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 compared to their controls, than RGR of plants that were not pregrown. However, a similar ranking of the cultivars for Al sensitivity was obtained irrespective of pregrowth period. The more Al tolerant BG35 consistently outyielded the Al sensitive IR45 under all Al treatments. A comparatively high Al-retention in roots and low Al transport rate to shoots of pregrown IR45 was the opposite of conditions in non-pregrown IR45. In BG35, uptake and transport of nutrients to the shoots were efficient at all Al levels. In IR45, particularly the uptake and distribution of P and Mg were disturbed by Al. It is suggested that a pregrowth or nursery period without Al reduces Al toxicity in both BG35 and IR45 at least up to 280 muM Al.