IMPROVEMENT OF YIELD AND QUALITY OF ROSELLE (HIBISCUS SABDARIFFA L.) PLANT BY USING NATURAL SOURCES OF PHOSPHORUS AND POTASSIUM IN CALCAREOUS SANDY SOILS

Two separate field experiments were conducted during 2013 and 2014 to study the effects of natural sources of phosphorus and potassium fertilizers as rock phosphate (RP) and feldspar (F) with or without biofertilizers comparing with chemical fertilizer (PK) on growth, yield and quality characteristics of roselle (Hibiscus sabdariffa L.) plant. The first experiment included phosphorus treatments (at different levels of rock phosphate; 150, 200 and 250 kg/fed) and the second one included potassium treatments (at different levels of feldspar; 250, 350 and 450 kg/fed), each comparing with recommended dose of chemical PK. The obtained results revealed that co-inoculation of PDB (Bacillus megaterium var. phosphaticum) and KDB (Bacillus mucilaginosus) in conjunction with direct application of rock phosphate at rates of 200 and 250 kg/fed and feldspar at rates of 350 and 450 kg/fed respectively, into the soil significantly increased the growth characteristics under the study (plant height, number of branches/plant, fresh and dry weight/plant,) along with yield (number of fruits/plant, fresh weight of fruit/plant, fresh and dry weight of sepals/plant, weight of seeds g/plant and weight of dry sepals kg/fed) comparing to chemical PK and other treatments. The highest growth and yield were obtained from plants treated with 200 kg/fed rock phosphate plus PDB in the first experiment and 350 kg/fed feldspar plus KDB in the second experiment. While PK treatment resulted in the highest acidity % and total anthocyanin content of dry sepals as compared to all the other treatments in the first and second seasons. Generally, the results suggest that the use of biofertilizer with rock phosphate or with feldspar are economical, environmental friendly and have potential to improve roselle yield and quality.