[Effects of Combined Application of Different Nitrogen Fertilizers and Biochar on Cadmium Uptake by Pakchoi (Brassica chinensis L.) in Cadmium Contaminated Soil].

Nitrogen is an essential nutrient element for crop growth, and biochar is a good material for soil remediation. In this study, a pakchoi (Brassica chinensis L.) pot experiment was conducted to investigate the effects of the combined application of three nitrogen fertilizers, including urea, ammonium sulfate, calcium nitrate, and biochar on pakchoi growth and cadmium (Cd) uptake from cropland soil contaminated by Cd. The results showed that the application of nitrogen fertilizers and biochar prompted pakchoi growth, and the biomass of pakchoi in the treatments of single applications of urea, ammonium sulfate, calcium nitrate, and biochar were significantly increased by 5.02%-32.9%, as compared with that in the control treatment without nitrogen fertilizer application. The biomass of pakchoi in the treatments of the combined application of nitrogen fertilizers and biochar were significantly increased by 8.84%-50.8%, as compared with that in the treatment of the single application of nitrogen fertilizer. Compared with that under the control treatment without nitrogen fertilizer application, the single application of urea significantly reduced soil pH by 0.27 and significantly increased the content of soil available Cd by 30.0%. The single application of ammonium sulfate significantly reduced soil pH by 0.33 and significantly increased Cd content in pakchoi by 29.2%, as compared with that in the control treatment. The single application of calcium nitrate had no significant effect on soil pH or Cd content in pakchoi, whereas the single application of biochar significantly increased soil pH by 0.35 and significantly decreased the content of soil available Cd and content of Cd in pakchoi by 57.4% and 53.7%, respectively, as compared with that in the control treatment. Soil pH in the treatments of the combined application of nitrogen fertilizers and biochar was significantly increased by 0.14-0.28, the contents of soil available Cd were decreased by 16.5%-30.1%, and the contents of Cd in pakchoi were reduced by 15.3%-28.6%, as compared with that in the treatment of single application of nitrogen fertilizers. In general, the application of biochar could adjust the effects of different nitrogen fertilizers on Cd availability in the contaminated soil. During the remediation process of heavy metal-contaminated cropland, nitrogen fertilizer should be selected and applied reasonably to obtain the maximum economic and environmental benefits.