Effects of nitrogen addition on above-standard Cd-contaminated soils in vegetable fields *

The aim of this study was to explore the effects of nitrogen application on Cd uptake by different kinds of leafy vegetables and on soil available cadmium (Cd) content in above-standard Cd-contaminated soils in vegetable fields. The study also comprehensively evaluated the effects of different nitrogen sources application with the aim of developing strategies to reduce Cd concentration in leafy vegetables by managing the application of nitrogen fertilizers. The experiment was carried out in an above-standard Cd-contaminated vegetable soil to investigate the effects of urea (CO(NH2)2), calcium nitrate (Ca(NO3)2), ammonium nitrate (NH4NO3) and ammonium bicarbonate (NH4HCO3) on yield, quality, Cd content, nitrogen content of two kinds of leafy vegetables — Brassica chinensis L. (BC) and Amaranthus mangostanus L. (AM). Soil DTPA-Cd