Roselle (Hibiscus sabdariffa L.) plant is a valuable medicinal crop in arid and semi-arid regions. The use of microbes as bio-fertilizers in enhancing crop production is more favorable than chemical fertilizers due to food safety. A pot experiment was conducted to explore the effect of Azotobacter chroococcum and Azospirillum brasiliense as a bio-fertilizer on the growth, yield, and quietly of roselle plants. Roselle seeds were mixed with the tested bio-fertilizer and cultivated on plastic pots filled with a sandy clay loam soil. The bio-fertilization significantly (p < 0.05) increased the growth, nutrients uptake, yield, and quality of roselle plants compared to the untreated plants. The inoculation of roselle plants with the bio-fertilizer increased the total chlorophyll, carotenoid, total anthocyanin (TAC), and total flavonel (TF) by 16.45, 26.10, 8.44, and 14.27%, respectively, above the control. The bio-fertilization increased the soil available nitrogen by 14.33% above the control, and increased the uptake of N, P, and K by 18.8, 17.81, and 12.75%. The bio-fertilization not only increased the quality of roselle plants but also increased the fresh and dry weights of sepals yield by 5.89 and 3.55%, respectively.

Although the use of biochar to promote plant growth has been reported by many researchers, the combined effect of prickly pear waste biochar (BC) and Azolla (AZ) in a field experiment on the roselle plants did yet receive attention. Therefore, the study aims to evaluate the effect of biochar and Azolla extract on the growth, production, and quality of roselle plants. The experiment treatments were in a completely randomized block design with three replicates. Biochar was added at rates of 0, 10, and 20 ton ha⁻¹and AZ was applied at rates of 0, 3, and 6% in addition to a control treatment. Biochar added at high rate (20 ton ha⁻¹) significantly increased the fresh and dry weights of sepals by 27.98 and 35.73%, respectively, compared to the control. The corresponding values were significantly increased by 11.89 and 11.85% over the control when Azolla was added at rate of 6%. The interaction effect of both BC and AZ treatments at high rate significantly increased the fresh and dry weight of sepals by 47.16 and 60.59%, respectively, compared to the control. The interaction effect of BC and AZ realized significant effect on soil properties, growth and yield, as well as pigments of roselle plants. This is a good evident means that BC and AZ applications separately or combined are considered promising materials for sustainable organic agriculture and safety food.

This study assesses the effects of organic fertilizers (vermicompost (V) and rabbit manure (R), combined with the bio-fertilizer Azotobacter chroococcum (AZ), on onion growth, yield, soil properties, and chemical metabolites over two growing seasons (2021/2022 and 2022/2023). The experiment, conducted at the Experimental Farm of Al-Azhar University, Assiut, Egypt, used a split-plot design with organic fertilizers as the main plot and bio-fertilizer treatments as subplots. The combined application of rabbit manure and Azotobacter (R + AZ) produced the tallest plants (59.64 cm and 63.23 cm), highest leaf number (10.71 and 10.82), and greatest bulb diameter (10.29 cm and 10.39 cm) in the first and second seasons, respectively. This treatment also resulted in the highest bulb length (9.49 cm and 9.66 cm), bulb weight (2.54 kg and 2.61 kg per 10 plants), and total yield (63.86 and 65.64 ton ha ⁻¹ ) in the first and second seasons, respectively. Additionally, organic fertilization improved several soil properties, including increased organic matter content, pH reduction, and changes in electrical conductivity. Azotobacter inoculation also increased the concentration of bioactive metabolites, such as phenolic compounds, flavonoids, and lipids, with the R + AZ treatment showing the most significant increases. This study demonstrates that the combination of rabbit manure and Azotobacter can enhance onion yield and nutritional quality, providing a sustainable approach to onion production by improving soil health and reducing the need for synthetic fertilizers. Graphical abstract A graphic abstract explains the importance of adding organic fertilizersand Azotobacter to improve the growth and yield of onion plants, as wellas the fertility and health of the soil.

Biochar derived from poultry manure increases nutrient availability and promotes plant growth. This study investigated the effect of biochar with mycorrhizal and/or plant growth-promoting rhizobacteria on soil fertility, chemical properties, oil, and seed yield of Black Cumin (Nigella sativa L.) plants. A split-plot design with three replicates was employed, with biochar derived from poultry litter (BC) applied at rates of 0, 5, and 10 t ha⁻¹, with beneficial microbes such as arbuscular mycorrhizal fungi (AMF) and plant growth-promoting rhizobacteria (PGPR) affecting the growth of Black Cumin plants, and some soil properties, such as pH, electrical conductivity (EC), soil organic matter (SOM) and fertility index (FI), showing significant differences (p ≤ 0.05) among biochar and/or bio-fertilizer treatments. All biochar treatments with or without bio-fertilizers significantly increased pH, EC, OM and FI in comparison to the control treatment. The results demonstrated that applying biochar at the highest rate (10 t ha⁻¹) increased fresh and dry capsule weights by 94.51% and 63.34%, respectively, compared to the control treatment (C). These values were significantly increased by 53.05 and 18.37%, compared to untreated plants when combined with AMF and PGPR. Furthermore, when biochar was applied in conjunction with both AMF and PGPR, fresh and dry capsule weights saw significant increases of 208.84% and 91.18%, respectively, compared to the untreated control treatment. The interaction between biochar, AMF, and PGPR significantly improved plant growth, yield, soil properties, and the fixed and volatile oil content of Black Cumin. These findings suggest that the combined application of biochar, AMF, and PGPR enhances nutrient availability and uptake, leading to improved growth and higher yields in Black Cumin plants, resulting in increased yield production.

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.

Use of compost and biofertilizer provides nutrients to crops and improves the chemical and physical properties of soils. A pot and incubation experiment was conducted to evaluate the effects of compost and Azotobacter chroococcum and Azospirillum brasiliense as biofertilizer on the carbon dioxide emission, nutrient availability under various incubation periods (0-time, 3, 7, 14, 30, 45, and 60 days) and growth, quality, and yield of roselle plants in pots. The treatments were control (C), compost 14 ton ha⁻¹ (T1) and compost + biofertilizer (T2). Results showed that the soil CO₂ flux was increased by 24.38, 33.16, 68.46, 70.17, 62.62, 50.34, and 47.49% over the control for 0-time, 3, 7, 14, 30, 45, and 60-days incubation periods, respectively, at compost + biofertilizer treatments. Available N was increased by increasing incubation period to two months 71.07, 63.67, 63.17, 57.77, 62.57, 57.89, and 58.01%, respectively, under treatment of compost + biofertilizer. The heaviest sepals of fresh and dry weights of sepals were gained by compost + biofertilizer treatment. Total anthocyanin and total flavonol increased by 29.68 and 32.45%, respectively, above the untreated plants. Also, the available N, P, and K content in the soil after the harvesting stage of roselle plants increased by 174.85, 178.24, and 50.96%, respectively, using compost with bio fertilizer treatment. Compost application with biofertilizer may, therefore, be a good strategy for increased to nutrient availability, growth parameter, and yield.