Conventional fertilization in the greenhouses of North China used excessive amounts of chemical and organic fertilizer, resulting in soil degradation and severe agricultural non-point source pollution. A nine-year study was conducted on a loamy clay soil in Shijiazhuang, Hebei province, to investigate the effects of reduced-fertilizer input regimes on soil property, bacterial diversity, nitrogen (N) cycling and their interactions. There were four treatments, including high organic + chemical fertilizer application rate and three reduced-fertilizer treatments with swine manure, maize straw or no substitution of 50% chemical N. Treatments with reduced-fertilizer input prevented soil salinization and acidification as in local conventional fertilization after being treated for nine years. In comparison to chemical fertilizer only, swine manure or maize straw substitution maintained higher nutrient availability and soil organic C contents. Fertilizer input reduction significantly increased bacterial richness and shifted bacterial community after nine years, with decisive factors of EC, Olsen P and C/N ratio of applied fertilizer. Soil chemical characteristics (EC, pH and nutrients), aggregation and C/N ratio of applied fertilizer selected certain bacterial groups, as well as N-cycling functions. Reduced-fertilizer input decreased the potential nitrification and denitrification functioning of bacterial community, but only in organic substitution treatments. The results of this study suggested that fertilizer input reduction combined with organic C input has potential in reducing non-point source pollution and increasing N-use efficiency in greenhouse vegetable production in North China.

The detoxification of crops grown in Cadmium (Cd)-contaminated acid soil has been widely studied, but for contaminated alkaline soil, there is still inadequate research or information. In order to investigate the effects of calcium and sulfur fertilizers, accompanied by different side elements, on the growth and Cd uptake of Spinacia oleracea grown in Cd-contaminated alkaline soil, the plants were subjected to five treatments, including calcium silicate (Ca-Si), calcium biphosphate (Ca-P), magnesium sulfate (S-Mg), ferric sulfate (S-Fe), and zinc sulfate (S-Zn), and a control group. The results showed that the S-Fe achieved the highest shoot fresh mass and dry mass and the highest shoot Cd concentration and accumulation, which were 30%, 68%, 4.6%, and 73% higher than the control group, respectively. The Ca-Si, Ca-P, S-Mg, and S-Zn reduced the root Cd concentration by 18%, 42%, 7%, and 49%, respectively, and reduced the shoot Cd concentration by 25%, 36%, 15%, and 27%, respectively, as compared to the control. S-Fe increases plant N uptake and photosynthesis, which is beneficial to biomass accumulation. Ca-P improves soil and plant P nutrition status, as well as plant K and Ca status, and helps alleviate plant Cd stress. Overall, calcium fertilizers accompanied by phosphorus have the potential to reduce plant Cd contamination risk, while sulfur fertilizers accompanied by iron show potential for enhancing Cd extraction.

To examine the safety of producing edible rapeseed in heavy-metal-contaminated farmland, field experiments were performed with 25 varieties of edible rapeseed on farmland lightly polluted with Cd in the central southern part of Hunan Province. Growing characteristics and Cd contents in rapeseed tissues were measured, and Cd uptake, translocation and removal potential were calculated. The results showed that the growth of 25 rapeseed varieties was not inhibited without withering or inconsistent changes in the shoot. The shoot and root Cd contents of rapeseed varieties ranged from 0.05 to 0.26 mg·kg⁻¹ and 0.04 to 0.26 mg·kg⁻¹, respectively. The bioaccumulation factor (BCF) showed that the shoot had a greater capacity for Cd transport than roots. The total Cd removed by rapeseed varieties ranged from 1.606 to 16.159 μg·plant⁻¹. There were significant differences in plant height, BCF of soil available Cd in the shoot, translocation factor (TCF) of Cd from root to shoot and Cd intake by rapeseed among the edible rapeseed varieties. Cluster analysis of Cd accumulation in the 25 rapeseed varieties indicated that Lvjin 1, Guanyou Qingjing and Guanyou brassica not only reduced soil pollution but also allowed for the production of safe leafy rapeseed, although Cd contents in the shoot of 25 rapeseed varieties did not exceed the national safety standards of China.

Heavy metals are a common type of contaminant found in soil. However, knowledge gaps still exist in the characteristics of the heavy metals in facility farmland soils. Therefore, a differential analysis was conducted on the heavy metal (Cd, Cr, Pb, As, Cu, Zn, and Ni) content in soils that were amended with different types of fertilizers (T1, organic fertilizer; T2, organic fertilizer and chemical fertilizer). Regression analysis was employed to demonstrate the trends of metal content changes with cropping durations (5, 10, 15, and 20 years). The Pearson correlation analysis was applied to investigate the correlation between soil nutrients and soil metals, and to determine the key factors influencing heavy metal concentration through the random forest model. The results indicated that the average concentration of Cd (0.148 mg·kg⁻¹) was higher than the soil background value but lower than the potential ecological risk threshold (0.3 mg·kg⁻¹, 6.5 < pH ≤ 7.5). The Cd content in soil where only organic fertilizer was applied was 0.118 mg·kg⁻¹, while the Cd content in soil where both organic fertilizer and chemical fertilizer were applied was 0.148 mg·kg⁻¹. There was no significant difference in Cd content between the two fertilization types. The regression analysis indicated a linear increasing trend in Cd content as the cropping duration increased. The Pearson correlation analysis showed that there were also significant correlations between pH and both As and Ni; between SOM (soil organic matter) and Cr, Cu, and Zn; as well as between Cd and EC (electrical conductivity). The random forest model exhibited high prediction accuracy when explaining the most significant factors influencing the concentrations of Cd, Cr, Pb, As, Cu, Zn, and Ni, with overall correlation coefficients (r) of 0.009, 0.44, 0.33, 0.04, 0.32, 0.61, and 0.65, respectively. Using Hakanson’s method to conduct an ecological risk assessment on the soil in the study area, it was found that the overall potential ecological risk level was relatively low. However, the proportion of moderate to high ecological risk associated with Cd elements was close to 40%, which requires special attention.

To investigate the differences in cadium (Cd) uptake and translocation among edible rapes and select suitable rape varieties for safe production, a field experiment was carried out with 25 varieties of edible rapes on a farmland polluted with Cd in the central souothern part of Hunan Province. The growing characteristics and Cd contents in rape tissues were measured, and the amount of Cd removed was calculated. The results showed that the growth of 25 rape varieties was not inhibited without withering or inconsistent changes in leaf and so on. The Cd contents in stem-leaf and root of rapes were in the range 0.05-0.26mg·kg-1 and 0.04-0.26mg·kg-1, respectively. Basing on BCF, the stem-leaf showed a greater capacity for Cd transport than root. And the total Cd removed by rape were 0.002-0.016 mg·plant-1. Except for plant height, BCF of soil available Cd from soil to stem-leaf, TCF of Cd from root to stem-leaf and Cd taken away by rape, there was no significant difference among edible rape varieties. Although Cd contents in stem-leaf of 25 rape varieties does not exceed the national safety standards, planting “Lvjin 1”, “Guanyou Qingjing” and “Guanyou brassica” not only reduced soil pollution but also allowed the production of safe leafy rape.