Abstract: 【Objective】 Chlorine (Cl) is an essential mineral element for plant growth, although Cl-containing fertilizers (such as ammonia chloride and potassium chloride) have a high concentration of Cl^? and a salt index that may be toxic to plants. Little information was currently known about the effect of long-term application of Cl-containing fertilizer on crop yield, soil fertility, and especially on soil biological fertility. Therefore, it was meaningful to explore the mechanism of the effect of the soil fertility on the soil biological fertility and the quantitative application of Cl-containing fertilizer’s impact on crop yield as well as improving soil fertility. 【Method】 Based on a 23-year field experiment in national monitoring station of soil fertility and fertilizer efficiency on purple soils, soil samples from treatments with no fertilizer (CK), applications of nitrogen, phosphorous and potassium fertilizer (NPK), applications of NPK together with rice straw return (NPK+S), and applications of Cl-containing NPK fertilizer with rice straw return ((NPK)Cl+S) were collected to study the soil microbiological community structure by the PLFA method, soil enzyme activities, and crop yield. 【Result】 Results showed that the long-term application of Cl-containing fertilizer ((NPK)Cl+S) reduced activities of urease, alkaline phosphatase, and catalase by 35.7%, 18.0%, and 69.8% the in rice cropping season and by 31.6%, 24.5%, and 75.6% in the wheat cropping season, respectively. Principal component analysis revealed that urease, alkaline phosphatase, and catalase were more representative than acidic, neutral phosphatase, and nitrate reductase as a comprehensive evaluation index. PLFA analysis showed that both the microbiological number and the abundance of (NPK)Cl+S treatments was the lowest, The biomass decreased 24.7% with NPK+S treatments relatively and a 43.2% reduction compared with the control. Chlorine fertilizer applications significantly affected the composition and quantity of microorganisms. The major behaviors are gram positive bacteria that may be relative to soil acidification and decline of soil enzyme activities. It’s also noted that (NPK)Cl+S treatments had a tendency to decrease crop yield. For example, rice and annual yield were decreased by 6.8% and 3.3% in average over 22 years. 【Conclusion】 Overuse of chloride containing fertilizer by applying ammonia chloride and potassium chloride together resulted in acidification of neutral purple soil, and then changed the soil microbial community and had the tendency to decrease soil biological fertility together with a declining rice yield. Thus we suggested not using two kinds of Cl-containing fertilizers together, especially for ammonia chloride which already has a high concentration of Cl^- and salt index.

Key words: chloride-containing fertilizer, soil enzyme activity, microbial community, rice and wheat yield, long-term experiment