The application of ionized water to irrigation, as a new type of water treatment technology, can improve the spatial distribution of water in soil and increase water utilization efficiency, which may affect the microbiological processes involved in nitrogen transformation and alter soil nitrogen supply capability. However, the effects of ionized water technology on soil organic nitrogen mineralization are still in need of further research. In this study, we investigated the soil organic nitrogen mineralization process with four different water additions: non-ionized fresh water (CK), ionized fresh water (DE), non-ionized brackish water (BCK), and ionized brackish water (BDE). By using a short-term laboratory incubation method, we monitored the changes of the inorganic nitrogen concentration in each treatment during the incubation process. We compared the net nitrogen mineralization and nitrogen mineralization rates in different treatments, and fitted the organic nitrogen mineralization process with three models (One-pool model, Special model, and EATM model). We divided the whole incubation process into three periods based on the differences of the organic nitrogen mineralization trends. The results demonstrated that when DE was compared with CK, the net nitrogen mineralization increased by 21.97% and the nitrogen mineralization rate increased by 20.42% in the latter incubation period. When BDE was compared with BCK, the net nitrogen mineralization decreased by 3.63%, and the nitrogen mineralization rate increased by 21.86% in the latter incubation period. When BCK was compared with CK, brackish water irrigation reduced the organic nitrogen mineralization intensity to a certain extent, with the net nitrogen mineralization decreased by 11.62% and the nitrogen mineralization rate decreased by 41.07% in the whole incubation process. When BDE was compared with DE, the net nitrogen mineralization decreased by 30.09% and the nitrogen mineralization rate decreased by 53.39% in the whole incubation process. The simulation model of the soil organic nitrogen mineralization process showed that the special model and EATM model are superior to the One-pool model. This study provides a theoretical basis for the popularization and application of ionized water irrigation in agricultural production.

Water ionization is an efficient physical water treatment technology, and crop water and nutrient use efficiencies can be improved using ionized water for irrigation. In order to explore the effect of ionized water on soil nitrification and nitrifying microorganisms, we conducted a laboratory soil incubation experiment with the addition of ionized water and ordinary water under different soil water contents (equal to 30%, 60%, 100% and 175% of the field capacity, θ_FC). During the soil incubation, we analyzed soil inorganic nitrogen transformation, ammonia oxidation gene abundances and nitrifying microbial community structure. The results showed that, no matter adding ordinary water or ionized water, the soil nitrification rate and the abundance of ammonia oxidizing bacteria in the 100%θ_FC treatment were significantly higher than those in other water conditions, while the abundance of ammonia oxidizing archaea was not affected by the soil water content. With the same soil water content, the nitrification rate of ionized water treatment was stronger than that of the ordinary water treatment. Although the absolute abundance of ammonia-oxidizing microorganisms in ionized water treatment was significantly lower than that of ordinary water (p < 0.05), the relative abundance of some dominant nitrifying microbial genera in the ionized water treatment was significantly higher (p < 0.05). The dominant genera may play a key role in the nitrification process. The results show that ionized water irrigation can significantly promote the nitrification of silt loam soil, especially under 100%θ_FC conditions, and may regulate soil nitrification by affecting some dominant nitrifying microorganisms. This study provides a theoretical basis for understanding the biological regulation mechanism of ionized water irrigation on soil nutrient transformation and for application of ionized water to field irrigation.