Effects of organic waste liquids on Chinese cabbage growth and cadmium accumulation in cadmium-contaminated soils

Organic waste liquids can be one of the most important sources of fertilizer used for sustainable production. However it is still unclear on the risks associated with their application in cadmium-containing contaminated farmland. This study aims to investigate the effects of organic waste liquids that are applied to the cadmium-contaminated soil on crop growth and environmental health risks. A series of potting experiments were performed on the growth and cadmium accumulation of Chinese cabbage. Five low-cost and commonly used organic waste liquids were taken as the pea fermentation liquid, corn syrup concentrate, chicken manure concentrated swamp liquid, molasses liquid, and amino acid mother liquor. These organic waste liquids were added into the soil at a dose of 2 mL/kg in advance, and then the Chinese cabbage was sown after 24h of standing time. Some parameters were determined in the Chinese cabbage grown for 35 days, including the growth indexes, photosynthetic characteristics, malondialdehyde (MDA) content, and antioxidant enzyme activities, together with the aboveground and underground cadmium concentrations of Chinese cabbage and cadmium in the active state in the soil. Moreover, the correlation and cluster analysis were utilized to clarify the correlation between the indicators and the relationship between the five organic waste liquids. The results showed that the pea fermentation liquor, corn syrup concentrate, chicken manure concentrate swamp liquid, and molasses liquid treatments promoted the growth of Chinese cabbage, except for the amino acid mother liquor. There was an increase in the net photosynthetic rate and a decrease in the MDA content of Chinese cabbage leaves under cadmium stress. Among them, the chicken manure-concentrated swamp liquid and corn syrup concentrate shared the most significant positive effect on Chinese cabbage growth. The height of Chinese cabbage plants increased by 15.21% and 12.58%, respectively, compared with the control treatment. Furthermore, the application of corn syrup significantly increased the aboveground and belowground dry weight of the Chinese cabbage plants by 21.66% and 68.75%, respectively, compared with the control treatment. There was also a significant increase in the activities of antioxidant enzymes in the Chinese cabbage plants (P<0.05), such as superoxide dismutase (SOD) and catalase (CAT). Corn syrup concentrate was the most effective in reducing the aboveground cadmium content of Chinese cabbage, followed by chicken manure concentrate treatment, which reduced the aboveground cadmium concentration of Chinese cabbage by 22.06% and 7.83%, compared with the control, respectively. Both of them also significantly reduced the cadmium transfer coefficient of Chinese cabbage plants (P<0.05). However, there was no reduce in the cadmium concentration and cadmium transfer coefficient in Chinese cabbage under the molasses liquid and the amino acid mother liquor. There was a significant increase in the cadmium enrichment coefficient, compared with the control treatment, indicating the potential health risks associated with their practical application. The corn syrup concentrate, chicken manure concentrated swamp liquid, molasses liquid and amino acid mother liquor increased the cadmium content in the soil effective state. Therefore, there were different effects of the five different organic waste liquids on Chinese cabbage growth and cadmium accumulation in the cadmium-contaminated soils. Corn syrup concentrate demonstrated great potential to promote crop growth with less cadmium uptake. The wide application was highly expected in real cases. This finding can provide a valuable reference for the resource utilization of organic waste liquid.