Sustainable Improvement of Soil Fertility and Phaseolus vulgaris Yield using Biochar, Azolla pinnata and Plant Growth-Promoting Rhizobacteria

Enhancing crop productivity while maintaining soil fertility remains a major challenge in arid and semi-arid regions, where sandy soils are low in organic matter and nutrient retention. Sustainable alternatives to chemical fertilizers are therefore essential. This study evaluated the effectiveness of integrating plant growth-promoting rhizobacteria (Bacillus circulans), Azolla pinnata and biochar as soil amendments to improve soil health and the productivity of Phaseolus vulgaris (common bean).

A field experiment was conducted over two consecutive growing seasons (2022-2023) at the Ismailia Agricultural Research Station, Egypt. Treatments included individual and combined applications of B. circulans, Azolla and biochar. Soil physicochemical properties, macronutrient availability (N, P and K), microbial activity, including dehydrogenase enzyme activity and plant growth and yield parameters were evaluated.

The integrated treatment significantly improved soil properties, increasing organic matter (0.66-0.71%) while slightly reducing pH (7.61-7.59) and electrical conductivity (1.11-1.09 dS m^-1). Nutrient availability was enhanced, with nitrogen reaching 48.10-49.10 mg kg^-1, phosphorus 5.62-6.62 mg kg^-1 and potassium 185-187 mg kg^-1. Microbial biomass and enzymatic activity were markedly stimulated. Plant growth traits, including biomass, leaf number, plant height and photosynthetic pigments, were improved, resulting in higher seed yield. These findings demonstrate that the synergistic use of biochar, Azolla and B. circulans effectively enhances soil fertility, microbial activity, plant growth and yield, providing a practical and eco-f riendly strategy for sustainable agriculture in nutrient-poor, semi-arid regions.