Abstract: The effect of irrigation water salinity and N application rate on soil microbial populations, soil respiration and soil microbial community functional diversity were investigated in a field experiment. The experiment used a 3×4 factorial design with three irrigation water salinization levels (fresh water, brackish water, or saline water) and four N application rates (0, 240, 360 or 480 kg N·hm^-2). The results showed that bacterial populations increased first and then decreased with increasing the irrigation water salinity, bacterial populations increased with the N application rate, but significantly reduced when excessive N was applied (>240 kg N·hm^-2). Fungi and actinomyces populations were significantly increased with the increase of irrigation water salinity, actinomyces populations decreased with the increase of N application rate. The bacteriatofungi ratio was 29% lower in the brackish water treatment and 86% lower in the saline water treatment than in the fresh water treatment. The highest bacteriatofungi ratio was observed in the 240 kg·hm^-2 treatment. Soil respiration decreased significantly with the increase of irrigation water salinity. Soil respiration in the fresh water treatment was 12% and 33% higher than that in the brackish and saline water treatments, respectively. Soil respiration increased with the increase of N application rate, and 360 and 480 kg N·hm^-2 treatments were 48% and 51% higher than that without N application. AWCD was decreased with increasing the irrigation water salinity, and the AWCD was 3% lower in the brackish water treatment and 13% lower in the saline water treatment than in the fresh water treatment. There were no significant differences in richness, Shannon’s index and evenness among the fresh water, brackish water and saline water treatments. Simpson index was the highest in the saline water treatment, and the highest soil microbial community diversity index was observed in the 240 kg N·hm^-2 treatment. Therefore, soil microorganisms and community functional diversity were affected significantly by saline water irrigation, and N application at proper rates could maintain soil microbial community activity and diversity.

Key words: microorganisms, soil pH, uptake, amino acids, maize