Abstract:Soil salination seriously affects the availability of soil nutrients, which restricts the development of agricultural productivity. The objective of this study is to elucidate the effects of soil salinity on nitrogen transformation of fertilizers applied conventionally in Hetao irrigation district of Inner Mongolia, China. Soils of different electrical conductivity [EC5:1, 1.46 dS/m (L), 2.19 dS/m (M) and 3.43 dS/m (H)] and added two chemical nitrogen fertilizers (urea and diammonium phosphate) were used to conduct the indoor thermostatic incubation experiment, and then the hydrolysis and nitrification of soils were determined. The results showed that, 1) inhibiting effect was found on the hydrolysis of urea when soil salinity increased, the net hydrolysis amount of treatment H decreased by 19.4% and 27.1% respectively compared with those of medium and low salt treatments. While medium salt showed a promoting effect on the hydrolysis of diammonium phosphate, and the net hydrolysis amount of treatment M increased by 33.6% and 4.3% respectively compared with those of low and high salt treatments; 2) high soil salinity postponed the beginning of nitrification, the nitrification of treatment H was delayed for about 3 days compared with L and M treatments. The effects of increasing soil salinity on the net nitrification amount of two nitrogen fertilizers were identical, first was promoted and then suppressed. The net nitrification amount of urea of treatment M was 8.6% and 9.1% higher than those of treatment L and H, respectively, while the net nitrification amount of diammonium phosphate of treatment M was 19.1% and 5.1% higher than those of L and H treatments, respectively; 3) in all soil salinities, diammonium phosphate was transferred more to mineral nitrogen than urea under the condition of equal amount of nitrogen input. In conclusion, soil salinity has a great impact on the transformation of nitrogen fertilizers, but the effects are different to different fertilizers. Increasing soil salinity can inhibit the release of fertilizer nutrients; However, appropriate amount of soil salinity may stimulate nitrification, and then can increase the risk of nitrogen leaching loss.