Integrated Soil Amelioration: Coffee Husk Biochar With TSP Fertilization Boosts Camelina [ Camelina sativa (L.) Crantz ] Productivity and Product Quality on Acidic Soil

Camelina is a resilient oilseed crop, but its productivity in acidic soils is limited by phosphorus fixation and poor soil fertility. This study examined the combined use of coffee husk biochar and triple superphosphate (TSP) fertilizer to improve soil properties, oil yield, and the nutritional quality of camelina seed cake in the acidic soils of the Hadiya Zone, Central Ethiopia. A split–split plot design was implemented during the 2024 cropping season using two cultivars (Zeytee-1 and Syria), four TSP rates (0, 23, 46, and 69 kg ha -1 ), and four biochar rates (0, 10, 12, and 14 t ha -1 ). Integrated biochar and TSP application significantly enhanced soil pH, total nitrogen, available phosphorus, and cation exchange capacity, with the highest amendment levels increasing available P to 45.3 ppm and CEC to 18.4 cmol kg -1 . Oil content improved with increasing TSP, reaching 45.7% in the Syria cultivar, while biochar reduced peroxide value, indicating better oil stability. Seed cake quality also improved, with crude protein rising to 39.2% and fiber fractions (ADF and NDF) increasing under higher amendment rates. Economic analysis showed that the greatest net benefit was achieved with moderate inputs (23 kg TSP ha -1 and 14 t biochar ha -1 for Syria), highlighting that economic optima differ from maximum yields. Overall, integrating biochar with TSP effectively ameliorated soil acidity, enhanced soil fertility, and improved both the quantity and quality of camelina products, offering a sustainable intensification strategy for acidic agroecosystems.