Abstract:

The accumulation of heavy metals in soil from vegetable growing greenhouses significantly affects the ecological environment and the safety of agricultural products. In order to clarify the input threshold for curbing the excessive accumulation of heavy metals in the soil of greenhouse agriculture, through field survey sampling and literature data collection, the present study analyzed the content status of six heavy metals in greenhouse vegetable soils and manure in Beijing−Tianjin−Hebei region in 2023: chromium (Cr), nickel (Ni), copper (Cu), zinc (Zn), cadmium (Cd), and lead (Pb). This study attempted to set an input threshold for Cd for the common cultivation of leafy fruit and vegetables fertilized with manure to reduce heavy metal accumulation during greenhouse vegetable production. Results showed that : (1) the average values for Cr, Ni, Cu, Zn, Cd and Pb heavy metals in the greenhouse vegetable soil in Beijing−Tianjin−Hebei region were 74.4, 26.6, 26.8, 97.7, 0.3 and 21.3mg·kg⁻¹, respectively, all below the background value stipulated by national standards (GB 15618−1995). Heavy Metal Soil Accumulation Index indicates that if the index value was more than 1, 61.4% of the sample points were measured as exceeding the predetermined background value for Cd. When the index value was more than 2, then 10.0% of the sample points used in data collection exceeded the background Cd value, which was significantly higher than that for the other heavy metals. (2) The Cd content did not exceed the corresponding standard value, while the heavy metal contents of Cr, Ni, Cu, Zn, and Pb in the manure of soil used for greenhouse vegetable planting were above the heavy metals standards of the agricultural industry standard (NY 525−2021). (3) From 2005 to 2025, the study for the fertilizer application of Cd for greenhouse vegetables in the Beijing-Tianjin-Hebei region showed that the Cd level decreased from 8.2mg·kg⁻¹ to 0.5mg·kg⁻¹with the increasing number of planting years, indicating that there was reasonable control of Cd content in the manure. When applying 15000kg·hm⁻² of manure, the thresholds of heavy metals Cd in the manure for control purposes were found to be 0.240 and 0.378mg·kg⁻¹, respectively, through input and output of heavy metals in leafy vegetables for Chinese cabbage and sesame leaf in the Beijing−Tianjin−Hebei region. The threshold for input of Cd heavy metals for fruit vegetables, represented by cucumbers, based on environmental capacity control, varied with manure application. The standards for input Cd based on soil pollution levels were set at 0.60, 0.40, and 0.24mg·kg⁻¹ for 20y, 30y and 50y of manure application, respectively, after 15000kg·ha⁻¹ of manure. These findings provide critical reference values to regulate sources of heavy metals in soils for greenhouse vegetables and would also assist in developing effective strategies for pollution prevention in the Beijing−Tianjin−Hebei region.

Key words: Greenhouse vegetable soil, Cadmium, Threshold, Leafy vegetables, Fruits and vegetables