Response of Roselle Plants (Hibiscus sabdariffa l.) to Pressed Olive Cake Compost Types and Potassium Fertilization Rates on Newly Reclaimed Soils at Siwa Oasis, Egypt

This investigation was carried out during the two seasons of 2013 and 2014 at the experimental farm of Matrouh Agricultural Research Station, Siwa Oasis, Matrouh Governorate, Egypt, (29.11° N latitude and 25.33° E longitude). The study aiming at evaluating the effect of two types of composts pressed olive cake (POC) and POC+CM (chicken manure) combined potassium fertilizer levels and their interactions on yield, yield components and some sepals chemical constituents of Rosella plants. The obtained results could be summarized as follows:- * The investigated compost types exerted significant effects on plant height, branches No. plant-1, seed yield (g plant-1) and seed yield (kg fed-1) of Roselle plants, and POC+CM compost exhibited the highest figures in 1st and 2nd seasons. The adopted K fertilization rates significantly affected the abovementioned parameters, which gradually increased due to increasing k fertilization ratefigures in the 1st and 2nd seasons. All the parameters were significantly influenced due to the interaction and the highest values were recorded under POC+CM compost and 48 kg K2Ofed-1 rate interaction in 1st and 2nd seasons. *Sepals yield and its components of Roselle plants were significantly influenced due to the tested compost types and K fertilization rates and interaction in 1st and 2nd seasons. Both POC+CM compost and 48 kg K2O fed-1 rate exhibited the highest figures of the abovementioned parameters 1st and 2nd seasons. The highest values of sepals yield and its components were attained due to POC+CM compost as interacted with 48 kg K2Ofed-1 rate in 1st and 2nd seasons. *N, P and K% of roselle petals were significantly influenced due to the investigated compost types and K fertilization rates. The highest N, P and K figures were attained with both POC+CM compost and 48 kg K2O fed-1 rate 1st and 2nd seasons. In addition, interaction of POC+CM compost and 48 kg K2O fed-1rate exhibited the highest values, however, the differences did not reach the significance level, and such trend was true in1st and 2nd seasons. * Chemical constituents of roselle sepals e.g. total carbohydrates, anthocyanin ascorbic acid contents and pH were significantly influenced due to K fertilization rates, whereas compost type exhibited similar trend, except with pH1st and 2nd seasons. POC+CM compost and 48 kg K2O fed-1 rate interaction still exhibiting the highest values of the abovementioned parameters, however, the differences did not reach the significance level, and such trend was true in1st and 2nd seasons. On conclusion, supplying POC compost combined with 48 kg K2O fed-1 resulted in higher values of sepals yield and quality and macronutrients uptake as well, however, it is advisable to replace POC compost by POC compost +CM which absolutely exhibited the highest values of the studied parameters under the present experimental conditions.