Objectives The change trends of soil EC and pH after long term application of chemical or organic fertilizers were studied, to provide data support for the replacement of chemical fertilizer by reasonable proportion of organic fertilizers in North China Plain.

Methods The long-term experiment, started from 2006, was located in Lingxian Experimental Station, CAAS, where the planting system was winter wheat–summer maize rotation and the tested soil was salinized fluvo-aquic soil. In the experiment, both organic and chemical fertilizers were separately applied in 10 nitrogen (N) rates, including 0, 60, 120, 180, 240, 300, 360, 420, 500, and 600 kg/hm². After 10 years and 20 growing seasons, the soil pH and EC were determined.

Results In treatments of chemical N 60, 120, 180 and 240 kg/hm², soil EC values were 232, 280, 220 and 258 μS/cm, respectively, and there was no significant difference with that in treatment of N 0; while in treatments of chemical N 300, 360, 420, 500 and 600 kg/hm², those were 320, 403, 513, 516 and 570 μS/cm, respectively, and were significantly higher than those in N 0–240 kg/hm². Soil pH in treatments of chemical N 0, 60, 120, 180, 240, 300, 360, 420, 500 and 600 kg/hm² fluctuated at 7.97, 7.96, 7.89, 7.88, 7.85, 7.83, 7.72, 7.53, 7.51 and 7.42, respectively, showing a significant linear correlation with inorganic N rates. At N level of 60, 120, 180 and 240 kg/hm², the difference of soil EC between organic and chemical fertilizer treatments were 9.9, –15.9, 26.4, 1.8 μS/cm, and differences in soil pH were negligible. When the N rates were 300, 360, 420, 500 and 600 kg/hm², the difference between the two fertilizer treatments were rapidly increased and became significant. The EC values in chemical N treatments were 42.1, 90.5, 195.1, 110.2, 187.5 μS/cm higher than those in organic fertilizers, and pH values were 0.08, 0.09, 0.18, 0.18, 0.14 lower than those in organic fertilizers, respectively.

Conclusions In North China Plain, long-term low and proper N input rates of chemical fertilizers will not lead to significant change of soil pH and EC values, but higher than 300 kg/hm² will increase soil EC and decrease pH significantly, while organic fertilizer will not produce significant variations in all the tested input levels. When the N input is higher than 300 kg/hm², the EC values in soils with chemical fertilizers are significantly higher than those with organic fertilizers, while the pH values are lower. So, when high N input is required in the salinized aquic-fluvo soil in North China, organic fertilizers should be considered and chemical fertilizer should be controlled within a reasonable level.