Effects of traditional Chinese medicine residue on plant growth and soil properties: a case study with maize (Zea mays L.).

Traditional Chinese medicine residue (TCMR) is the solid substances remaining after the extraction of pharmaceutical ingredients from medicinal plant materials, which include abundant soil nutrients. However, TCMR is nearly lost as domestic garbage, which not only occupies a large amount of land but also leads to the waste of resource, as well as causing the eco-environment potential pollution. Therefore, we implemented this study to assess whether TCMR could be used as an organic fertilizer in agricultural practices for realizing waste resource utilization, improving soil fertility, and enhancing plant growth. The results showed that (1) application of TCMR could improve soil fertility, particularly in enhancing the soil contents of SOM, TN, NaOH-N, NaHCO3-P, and HNO3-K; (2) the higher application ratios of TCMR (0.8-1.0%) that increased the soil EC values would cause the risk of soil secondary salinization; (3) the lower application ratios of TCMR (0.2-0.6%) has a better positive effect on improved the maize seedlings' physiological parameters and photosynthetic performance than the higher application ratios; (4) although application of TCMR lead to the heavy metal (Cr, Pb, Cd, As, and Hg) content increased in soil, there was no ecology risk under below 0.8% application ratio, compared with the China soil risk control standards, geo-accumulation index (Igeo), and pollution load index (PLI). Thus, TCMR could potentially be used as an organic fertilizer in agricultural practices. This approach is an effective strategy not only for achieving TCMR disposal but also for realizing waste resource utilization, as well as for improving soil fertility and plant growth.