LAUSR

Abstract Excessive nitrogen (N) fertilizer is often applied to soils to improve crop productivity, which leads to a reduction in N efficiency and an increase in N loss to groundwater. To investigate the effects of fertilizers on N loss, the different N forms in leachates and soil profiles were determined by leaching column experiments. The treatments included fertilizer applications of urea (U), amino acid (A), potassium nitrate (K), and manure (M), as well as a control without fertilizer (CK). The results showed that the total N loss (TL) ranged from 58.85 kg N ha −1 a−1 to 905.34 kg N ha −1 a−1, and that the percentage of N loss (PL) to the total N was between 2.09% and 32.14%. Exogenous N fertilizer addition resulted in a higher TL and higher PL, and thus lower amounts of total dissolved N (TDN) in soils. With respect to the different forms of N, NO 3 − -N and dissolved organic N (DON) were the main contributors to the TL, accounting for 46.96%–98.68% and 1.12%–50.88%, respectively. Notably, urea and manure addition resulted in higher DON losses, which were 2.34-fold and 1.04-fold that of CK. Furthermore, the relative abundances of nitrification-related and organic matter degradation-related bacteria in deep soil layers were 1.13–1.64 and 1.01–1.02 times higher than those in CK. The sources of DON included the direct leaching of DON contained in the fertilizers, and the enhanced DON derived from native soil organic matter through the improvement of the related microorganisms in deep soils.