Improving properties of sandy soil and production of Phaseolus vulgaris cultivation using Azolla pinnata, eggshells, and biochar.

Sandy soils are characterized by low organic matter content, weak nutrient retention, and limited water-holding capacity, which restrict crop productivity in arid and semi-arid regions. This study evaluated the individual and combined effects of biochar, Azolla pinnata, and eggshell powder on soil properties and the productivity of common bean (Phaseolus vulgaris L.) grown in sandy soil. Field experiments were conducted during two consecutive growing seasons (2021-2022) at the Ismailia Agricultural Research Station, Egypt, using a randomized complete block design with eight treatments and three replicates. Soil chemical properties, photosynthetic pigments, vegetative growth, biomass accumulation, and yield parameters were evaluated. The combined application of biochar, Azolla, and eggshell powder significantly improved soil fertility compared with the control treatment. Soil organic matter increased to 0.70%, while available nitrogen, phosphorus, and potassium reached 51.10, 6.67, and 200 mg kg⁻¹, respectively. The integrated treatment also enhanced chlorophyll content, plant growth, biomass production, and seed yield across both seasons. Correlation analysis indicated strong positive relationships between soil organic matter, nutrient availability, and crop productivity. These results demonstrate that the integrated application of biochar, Azolla pinnata, and eggshell powder can effectively improve soil fertility and enhance the productivity of Phaseolus vulgaris in sandy soil systems.