Effect of Natural Zeolite Application on Nitrite Concentrations in Rape (Brassica campestris L.) in Pb-Contaminated Soils in Peri-Urban Areas

Peri-urban soils are polluted by lead (Pb) due to urban development in China. Natural zeolites have been widely used for remediating heavy metals in soils, but the effects of natural zeolite application on nitrite concentration in rape have not been studied. Pot experiments were carried out to investigate using a random complete block design. Zeolite application and Pb contaminants in soil caused significant decreases in nitrite concentrations in rape. Chlorophyll a (Chl-a), chlorophyll b (Chl-b), and chlorophyll a + b (Chl-a + b) in rape decreased as levels of Pb contamination increased. Pb contamination reduced the photosynthetic activity of rape, and appears to limit the transformation of nitrate to nitrite, but pose food risk. Zeolite application caused a significant increase in soil pH, with a variation range of 0.5. The increase in soil pH reduced nitrite accumulation in soil by enhancing activity of ammonia-oxidizing bacteria. The content of soil aggregates > 0.25 and > 2.00 mm all increased in response to the application of zeolite. Increases in soil aggregates could effectively control excessive release of nitrogen (N) accumulated in soils, which would reduce uptake of N by plants. These results indicate that the application of zeolite is an eco-friendly and effective way to improve the quality of rape growing in peri-urban areas.