Growth and Proximate Composition of Amaranth as Influenced by Biochar Amendment Rates and Endophytes Application Under Field Conditions

Abstract

Soil fertility management remains a major challenge in vegetable crop production, particularly in container gardening systems. Biochar soil amendment and the application of exogenous endophytes are two technologies with potential to improve plant performance under container production conditions. This pot experiment investigated the combined effects of rice husk biochar (RHB) amendment and foliar application of endophytes on soil fertility, nutrient availability, biomass production, and nutritional composition of Amaranthus hybridus under field conditions at the University for Development Studies, Ghana. The five treatments used were 100% topsoil (control). foliar application of mixed bacterial and fungal endophytes products, and three topsoil-to-RHB ratios (90:10, 75:25, and 50:50, w/w), each combined with foliar application of the endophyte products. The completely randomized design with three replications was used. The application of biochar at different rates in combination with endophytes significantly (p<0.05) improved soil chemical properties and moisture retention. The moderate biochar rate (25% RHB + endophytes) particularly enhanced nutrient availability, with soil N, P, and K concentrations of 0.269%, 6.31 mg/kg, and 4.41 cmol/kg, respectively, as well as soil moisture content. This treatment also promoted vegetative growth, producing the tallest plants (42 cm), the highest biomass yield (197.7 g), and the greatest protein content (11.44%) in the edible leaves. Endophyte application alone also improved plant growth parameters relative to the control. Nutritional analysis further showed that the combined application of biochar and endophytes increased the dry matter, ash, fibre, and protein contents of the leaves. Overall, the application of 25% RHB with 75% topsoil, combined with foliar endophyte application, improved soil fertility, plant growth, biomass production, and nutritional quality of Amaranthus. The moderate biochar–endophyte treatment could therefore be considered for container-based vegetable production; however, biochar application should be carefully managed rather than routinely applied because of its potentially long-lasting effects on soil properties.