POTENTIAL EFFECTS OF FELDSPAR AND BIOCHAR-BASED CO-INOCULATION OF RHIZOBACTERIA IN COWPEA PLANTS

Abstract

In light-textured areas, soil deterioration lowers available nutrients and biological activity, therefore endangering the yield of dryland grain legumes. This study investigates whether combining feldspar, biochar, and two Bacillus strains (B. circulans and B. amyloliquefaciens) with plant growth–promoting rhizobacteria (PGPR) can improve soil quality and cowpea performance under sandy conditions. Twelve treatments combining feldspar, biochar, and two Bacillus strains against a fertilized but nonamended control were tested in a two-year field experiment (summer 2021 and 2022) conducted at the Ismailia Research Station, Egypt, using a randomized complete block design. Before sowing and after harvest, soil samples (0–30 cm) and plant measurements were gathered to evaluate physical properties, electrical conductivity, organic matter, accessible nitrogen (N), phosphorus (P), and potassium (K), soil dehydrogenase activity, chlorophyll pigments, growth characteristics, yield components, and seed composition. While feldspar and biochar individually enhanced soil conditions and cowpea performance compared with the control, their combination with rhizobacterial inoculation produced greater responses. The combined treatment with biochar + B. circulans + B. amyloliquefaciens continuously maximized soil N, P, and K availability, dehydrogenase activity, plant height, leaf number, branch number, pod characteristics, and seed carbohydrate and macronutrient concentrations across seasons. In total, integrating feldspar and biochar with multi-strain rhizobacterial inoculation provides a strong, scalable approach to improve soil fertility, nutrient cycling, and cowpea productivity in low-nutrient sandy soils; it is also a promising path to reduce reliance on traditional mineral fertilizers in arid and semi-arid agroecosystems.