Compost and Non-Symbiotic Nitrogen Fixers to Reduce Inorganic-N Rates for Roselle (Hibiscus sabdariffaL.)

Organic and biofertilizers can be good tools in increasing plant growth and yield without negative impacts in environmental ecosystem. Compost and non-symbiotic nitrogen fixers were used in a pot experiment to reduce inorganic nitrogen (N) rates for roselle. The experiment consisted of five treatments i.e. C = without any N fertilization, T1 = 100% of recommended N does from urea, T2 = 100% of N from compost (2.5% N) at a rate of 12 ton ha −1, T3 = 75% of inorganic N + 3 ton ha −1 of compost, and T4 = 50% of inorganic N + 6 ton ha −1 compost. The compost and biofertilization increased the soil quality and enhanced the synthesis of chlorophyll and nutrients uptake by roselle plants compared to the full inorganic N fertilization. Nitrogen use efficiency (NUE) affected significantly (p < 0.05) by the compost and biofertilization. The maximum NUE (58%) was recoded in the treatments received 75% of inorganic N + 3 ton ha −1 of compost. The mixtures of compost and inorganic N fertilization under the biofertilization gave the highest values of the total anthocyanin and total flavonol in the sepals of roselle plants. The maximum dry weight of sepals was obtained from the T4. T4 improved growth, yield, and quality of sepals in comparison with the full inorganic N fertilization. The inorganic N rates for roselle can be reduced by 50% by the application of 6 ton ha −1 of compost and the inoculation with bio-fertilizer containing a mixture of Azotobacter and Azospirillum.