Effects of Phosphorus and Mycorrhiza on Growth of Okra at High Soils Acidity   Bunjirtluk Jintaridth W. Keltjens and Charoen Charoenchamratcheep   ABSTRACT         Plant growth on acid soils is inhibited mostly due to Al toxicity and disturbed nutrient uptake. Due to problems of high soil acidity plant growth on acid soils can be reduced very severely. At extreme soil acidity the excess of the cations Al3, H+, Mn dominates, but especially Al toxicity causes impaired root development. For medium soil acidity, there are possible nutrient deficiencies such as P, Mg, Ca, K. The possibilities were investigated how to ameliorate soil acidity not only by liming, but also by selection of plant species or cultivars that are tolerant to soil acidity and fertilizing   the soil to overcome the nutrient deficiency problems.  Effects of a fertilization with phosphorus and VAM were studied on growth of okra at high soil acidity at Wageningen Agricultural University in 1995. For all treatments, 3.5 Kg dry soil was put in plastic pots. The experiment was carried out in a greenhouse during the period September-December 1995 at 25 oC and at a light intensity about 50 W/m2 (HPLlamps). For the low pH (4.5) treatment, five levels of phosphate were supplied : 0.1, 0.25, 0.5, 1.0 and 2.0 g P2O5 per pot for superphosphate (18% P2O5), Rock-P with and without VAM. For the optimal pH (pH 5.5), superphosphate treatment 2.0 g P2O5 per not were supplied. It was found that applying at low rate of P, rock phosphate in combination with a mycorrhiza resulted in higher shoot dry weight than rock phosphate without mycorrhiza or superphosphate. With increasing rates of P supply superphosphate seemed to be more effective than rock phosphate.         Key words : okra, Mycorrhiza, acid soil, phosphorus, rock phosphat