尿素氮添加对黑钙土酸化速率及酸中和容量的影响

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

【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 g m^(−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)显著下降,土壤酸化速率(SAR)随N添加量的增加及交换性盐基总量的降低而增大,N添加的土壤酸化速率为0.017∆pH a^(−1)g^(−1)m^(2)a。用二次多项式拟合土壤酸缓冲曲线其决定系数(R^(2))较高,N加量10 g m^(−2)a^(−1)以下各处理的土壤初始pH降低至5.0、4.5、4.0时的酸中和容量ANC_(pH5.0)、ANC_(pH4.5)、ANC_(pH4.0)均无显著差异,N添加量15和20 g m^(−2)a^(−1)处理的ANC_(pH5.0)、ANC_(pH4.5)、ANC_(pH4.0)显著下降。【结论】草原黑钙土酸化速率对外源N添加敏感;土壤交换性盐基离子含量高,对外源H+的输入具有较好的缓冲作用;尿素添加导致的土壤酸中和容量(ANC)下降主要受土壤初始pH和交换性盐基总量下降的影响。

[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)m^(2)a.The best fitting model for soil acid titration curves was the quadratic curve fitting model,which had the greatest determination coefficient(R^(2)).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).