Effect of organic fertilizers mixed with ginkgo leaf biochar on lettuce growth and soil chemical properties

Abstract The application of biochar combined with organic fertilizers is increasingly being recognized as a sustainable strategy for improving soil quality and crop productivity. Ginkgo leaves are abundantly generated but rarely utilized because of their allelopathic effects and poor degradability. In this study, the allelopathic activity of ginkgo leaf biochar produced at three different pyrolysis temperatures (300 °C, 500 °C, and 700 °C) was evaluated through seed germination tests using six species of seeds—three crops (kale, lettuce, and perennial ryegrass) and three weeds (annual bluegrass, barnyard millet, and slender amaranth). Additionally, the effects of organic fertilizer mixed with different ratios (10% and 30%) of ginkgo leaf biochar on soil chemistry and lettuce growth were also evaluated. Seed germination assays revealed that biochar produced at 300 °C and 700 °C inhibited germination in most species, while biochar produced at 500 °C showed no allelopathic effects on any of the tested species and promoted germination in lettuce and kale. Soil chemical properties indicated that application of organic fertilizer mixed with ginkgo leaf biochar increased soil pH, total carbon, and total nitrogen content. Notably, soil total nitrogen content increased with higher pyrolysis temperatures and mixing ratios of ginkgo leaf biochar. In lettuce growth trials, organic fertilizers mixed with biochar produced at temperatures above 500 °C significantly increased the fresh weight, leaf length, leaf width, and leaf number of lettuce. Applying organic fertilizer mixed with 30% biochar produced at 500 °C increased fresh weight by 63.6% relative to the control (organic fertilizer without biochar). Ginkgo leaf biochar produced at moderate temperatures (around 500 °C) and applied at higher ratios effectively enhanced crop growth, promoted germination, and improved soil fertility. These results suggest that this approach can promote the recycling of biomass and contribute to sustainable agricultural productivity.