Combined application of algal biochar and nanobiochar enhances soil quality and rice growth

Soil degradation caused by intensive cultivation and excessive fertilizer use threatens sustainable crop production. Although biochar improves soil quality, the combined effects of algal biochar (ABC) and nanobiochar (NBC) remain unclear. This study evaluated the influence of ABC and NBC on soil properties, nutrient status, microbial biomass, and rice performance over two years under field conditions. ABC was produced from mat-forming algae at 450 °C, while NBC was derived from wheat straw. Twenty-three treatments, with individual and combined applications ± commercial fertilizer, were arranged in a randomized block design. Combined ABC + NBC significantly improved soil properties, increasing dissolved organic carbon by up to 90%, soil nutrients by 30–45%, and microbial biomass carbon and nitrogen by 70–85% compared to control and CF treatments. These improvements enhanced plant performance, increasing chlorophyll content by 30% along with fresh biomass, plant height, and root biomass. Yield traits, including grains per spike and 100-grain weight, also improved significantly, resulting in up to 60–70% higher grain yield under combined ABC and NBC treatments. The combined application of ABC and NBC outperformed individual treatments and conventional fertilizers by improving soil fertility, microbial activity, and rice productivity, while reducing reliance on fertilizers.