Abstract: Few studies have assessed the effects of different forms of nitrogen combined with low-molecular organic carbon application on plant growth and quality. Residue after evaporation (RAE) is a kind of waste liquid generated during industrial vitamin C (VC) production, which is mainly composed of 2-keto-L-gulonic acid, a low-molecular-weight organic acid. We investigated the effects of urea (amide nitrogen, Urea-N), potassium nitrate (nitrate nitrogen, NO₃^--N), and ammonium chloride (ammonium nitrogen, NH₄⁺-N) combined with RAE on the growth and quality of non-heading Chinese cabbage (Brassica campestris ssp. chinensis). The results showed that the combined application could significantly improve nitrogen uptake efficiency and partial factor productivity of nitrogen fertilizer. RAE promoted the conversion of other forms of nitrogen into the easily absorbed form, NO₃^--N, which was the key to improve nitrogen uptake efficiency. The nitrogen uptake efficiency, contents of VC, soluble protein and nitrate in RAE+NO₃^--N treatment were the highest. The partial factor productivity of nitrogen fertilizer, biomass and soluble sugar accumulation levels under RAE+NH₄⁺-N treatment were the highest, which was closely related to the proportion of photosynthetic pigment components. In addition, the response of soil available P and available K content to RAE and different nitrogen fertilizer combinations was different, which potentially led to the difference of biomass and quality. When RAE was applied in combination with Urea-N or NH₄⁺-N, crop quality could be greatly improved, but there was no significant difference between the two combinations. Comprehensively considering nitrogen uptake efficiency, partial factor productivity of nitrogen fertilizer, crop yield and quality, the combination of RAE and NH₄⁺-N was the best choice.

Key words: nitrogen uptake efficiency, partial factor productivity of nitrogen fertilizer, organic acid, vitamin C, nitrate