Soil amendment strategies for continuous cropping obstacles in foxtail millet (Setaria italica L.): impacts on growth, nutrient partitioning, and yield formation

Continuous cropping obstacles (CCOs) severely constrain foxtail millet ( Setaria italica L.) productivity by impairing soil health and disrupting nutrient cycling. This study evaluated fourteen soil amendment treatments to determine their efficacy in ameliorating CCOs in an outdoor pot experiment. Plant growth, photosynthetic pigments, biomass allocation, yield components, nutritional quality, and the physicochemical properties of leaves, roots, and soil were assessed at the maximum biomass stage. Based on the pot experiment, compared with continuous cropping, corn stalk biochar and humic acid significantly increased plant height, stem diameter, leaf SPAD, leaf thickness, leaf area, spike length, and specific leaf weight. Rotation with foxtail millet and Sorghum bicolor improved plant height, leaf SPAD, leaf thickness, leaf area, spike length, root forking, specific root surface area, soil total nitrogen, and available potassium ( P < 0.05). Humic acid application increased leaf total nitrogen and phosphorus, root potassium, and soil available potassium. Bacillus inoculation increased leaf organic carbon when applied as B. subtilis and B. megaterium , while B. mucilaginosus increased root phosphorus. Corn stalk biochar also increased leaf tissue density and soil organic carbon, whereas earthworm castings increased soil total and available nitrogen. Rotation with Vigna radiata promoted leaf expansion, while S. bicolor rotation enhanced root elongation. Redundancy analysis and hierarchical partitioning identified stem weight (26.62%), grain total starch (7.79%), root total nitrogen (5.10%), and leaf total phosphorus (1.99%) as the primary variables associated with yield components. The results provide a theoretical basis for understanding the responses of foxtail millet and continuously cropped soils to different individual amendments under pot experimental conditions.