尿素氮添加对黑钙土酸化速率及酸中和容量的影响

[目的]探讨尿素氮添加对草原黑钙土酸化指标的影响及交换性盐基离子的酸缓冲机制.[方法]依托内蒙古额尔古纳草甸草原尿素添加试验,测定了尿素添加(加N量0、2.5、5、10、15、20 gm-2 a-1)4年后的黑钙土酸化参数.[结果]研究发现随尿素氮添加量的增加,表层(0～10 cm)土壤pH和交换性盐基总量(SEB)显...

Effects of Urea Nitrogen Addition on Acidifying Rates and Acid Neutralizing Capacity of a Chernozem

  Objective  The objective was to explore the effects of urea nitrogen (N) addition on acidification indices and the acid buffering mechanisms of exchangeable base cations in a grassland chernozem.  Method  Based on the urea addition (with N addition rates 0, 2.5, 5, 10, 15 and 20 g m?2 a?1, respectively) experiment conducted in a meadow grassland chernozem in Erguna, Inner Mongolia, soil acidifying variables were examined after 4 years of N additions.  Result  Significant decreases in pH and the sum of exchangeable base cations (SEB) of the topsoil (0-10 cm) were found with increasing urea N addition rates. Soil acidifying rate (SAR) increased with the increasing N addition rates and decreasing SEB, and the SAR with N addition was approximately 0.017 ?pH a?1 g?1 m2 a. The best fitting model for soil acid titration curves was the quadratic curve fitting model, which had the greatest determination coefficient (R2). Soil acid neutralizing capacities (ANC) at the reference pH 5.0, 4.5 and 4.0 (ANC_{pH 5.0}, ANC_{pH 4.5}, and ANC_{pH 4.0}) were not significantly different among treatments with N addition rates lower than 10 g m?2 a?1, while ANC_{pH 5.0}, ANC_{pH 4.5}, and ANC_{pH 4.0} decreased significantly in treatments with N addition rates 15 and 20 g m?2 a?1.   Conclusion  Soil acidifying rate (SAR) of the grassland chernozem was sensitive to exogenous N inputs. The higher exchangeable base cations exhibited a better buffering capacity to exogenous H+ inputs. The decrease in soil acid neutralizing capacity (ANC) induced by urea N addition was mainly affected by the decreases in initial soil pH and the sum of exchangeable base cations (SEB).