Exploring Sustainable Fertilization Strategies Involving Biochar, Compost, and Inorganic Nitrogen: Impact on Nutrient Uptake, Yield, Phytochemical Accumulation, and Antioxidant Responses in Turnips

Abstract

The effect of fertilization strategies involving biochar, compost, and inorganic N on growth and phytochemical accumulation in turnips was studied in a greenhouse pot experiment. The experiment was carried out with six fertilizer treatments: unfertilized soil (US), compost (120 g/pot) + biochar (20 g/pot) (C + B), compost (120 g/pot) + 0.5 g N/pot (C + 0.5 N), biochar (20 g/pot) + 0.5 g N/pot (B + 0.5 N), compost (120 g/pot) + biochar (20 g/pot) + 0.5 g N/pot (C + B + 0.5 N), and inorganic fertilization (pre-plant mineral fertilizer + 1 g N/pot (PF + N)). Compost, biochar, and pre-plant mineral fertilizer were incorporated into the top 10 cm of soil, while inorganic N was applied weekly in equal amounts. The application of biochar with C + 0.5 N, compared to C + 0.5 N alone, reduced plant Ca and Mg uptake but did not affect dry biomass production. Using compost + 0.5 N, with or without biochar, proved to be a viable and sustainable strategy, achieving high dry biomass yields similar to inorganic fertilization but with lower inorganic N and no addition of the other inorganic nutrients. The biomass increase was due to enhanced nutrient uptake, resulting from the synergy between compost and the application of a reduced amount of N. The co-applications reduced nitrate levels in both shoots and roots and left the soil more fertile than soil fertilized with inorganic fertilization. Fertilization strategies differently affected the accumulation of ascorbic acid, total phenols, polyphenol oxidase, and proline in roots and shoots. Inorganic fertilization enhanced ascorbic acid and total phenols in shoots, while the combination of compost, biochar, and 0.5 N was more effective in roots, suggesting that fertilization strategies should be tailored to tissue-specific goals.