Effects of long-term application of chlorinated fertilizer on nitrification and ammonia oxidizing microorganisms in brown soil

Objectives Ammonia-oxidizing microorganisms are the main drivers of ammonia oxidation process. Ammoxidation process as a rate-limiting step of nitrification plays an important role in nitrogen cycle. We used the soil of a long-term experimental site in the brown soil of Shenyang Agricultural University, the effects of continuous application of high chloride and low chlorinated fertilizer on the nitrification and ammonia oxidizing microorganisms.

Methods The long-term experimental was carried out using equal amounts of N, P and K with high and low chlorine treatment, with a total of 8 treatments: T1, no fertilization control; T2, application of urea; T3, urea + potassium chloride; T4, urea + calcium superphosphate; T5, urea + calcium superphosphate + potassium chloride; T6, urea + monoammonium phosphate + potassium chloride; T7, urea + chloroammonium phosphate + potassium chloride; and T8, nitrophosphate fertilizer + superphosphate + potassium chloride. Among them, urea + chloroammonium phosphate + potassium chloride was high chlorine treatment. The 0–20 cm soil samples were collected and the abundance of ammonia-oxidizing bacteria (AOB) and archaea (AOA) was determined by the real-time PCR. Combined with soil nitrification potential and basic chemical properties, analysis was conducted on the effects of long-term application of chlorinated fertilizer on the abundance of microorganisms and the main environmental factors affecting the abundance of ammonia-oxidizing microorganisms.

Results Long-term fertilization reduced soil pH, especially with the high Cl treatment. In the high Cl treatment, soil nitrification potential was also significantly lower than other treatments. The nitrification potential of soil treated with phosphate fertilizer was significantly higher than that without phosphorus treatment. The abundance of AOA in each treated soil was significantly higher than that of AOB and the abundance of AOA and AOB in high Cl treated soil was significantly lower than other fertilization treatments, and the soil nitrification potential was significantly and positively correlated with AOA and AOB.

Conclusions After 34 years of continuous application of high chloride fertilizer, the abundance of AOA and AOB in brown soil was significantly reduced, and the nitrification potential was inhibited. The test results can provide a reference for rational application of chloride fertilizers to regulate AOA and AOB, which in turn regulates soil nitrogen cycle.