State Key Laboratory of Soil and Sustainable Agriculture, Institute of Soil Science, Chinese Academy of Sciences, Nanjing 210008, China.
J Environ Sci (China). 2012;24(4):682-9. doi: 10.1016/s1001-0742(11)60832-2.
The mechanisms for the effects of ammonium-based fertilizers on soil acidification in subtropical regions are not well understood. Two Ultisols collected from cropland and a tea garden in Anhui and Jiangxi Provinces in subtropical southern China, respectively, were used to study the effects of urea and (NH4)2SO4 on the nitrification and acidification of soils with incubation experiments. Nitrification occurred at very low pH with no N fertilizer added and led to lowering of the soil pH by 0.53 and 0.30 units for the soils from Jiangxi and Anhui, respectively. Addition of urea accelerated nitrification and soil acidification in both Ultisols; while nitrification was inhibited by the addition of (NH4)2SO4, and greater input of (NH4)2SO4 led to greater inhibition of nitrification. Ammonia-oxidizing bacteria (AOB) played an important role in nitrification in cropland soil under acidic conditions. Addition of urea increased the soil pH at the early stages of incubation due to hydrolysis and stimulated the increase in the AOB population, and thus accelerated nitrification and soil acidification. At the end of incubation, the pH of Ultisol from Jiangxi had decreased by 1.25, 1.54 and 1.84 units compared to maximum values for the treatments with 150, 300 and 400 mg/kg of urea-N added, respectively; the corresponding figures were 0.95, 1.25 and 1.69 for the Ultisol from Anhui. However, addition of (N-H4)2SO4 inhibited the increase in the AOB population and thus inhibited nitrification and soil acidification. Soil pH for the treatments with 300 and 400 mg/kg of (NH4)2SO4-N remained almost constant during the incubation. AOB played an important role in nitrification of the cropland soil under acidic conditions. Addition of urea stimulated the increase in the AOB population and thus accelerated nitrification and soil acidification; while addition of (NH4)2SO4 inhibited the increase in the AOB population and thus inhibited nitrification.
在亚热带地区，铵态肥料对土壤酸化的影响机制尚不清楚。本研究分别采用来自中国南方亚热带地区安徽省和江西省农田和茶园的 2 个土壤（赤红壤）进行培养实验，研究了尿素和（NH4）2SO4对土壤硝化和酸化的影响。在未添加氮肥的情况下，土壤在非常低的 pH 值下就发生了硝化作用，导致江西和安徽土壤的 pH 值分别降低了 0.53 和 0.30 个单位。添加尿素加速了两种赤红壤的硝化和酸化；而添加（NH4）2SO4则抑制了硝化作用，并且（NH4）2SO4 的添加量越大，硝化作用的抑制作用就越大。在酸性条件下，氨氧化细菌（AOB）在农田土壤的硝化过程中起着重要作用。添加尿素由于水解作用而在培养的早期阶段增加了土壤 pH 值，并刺激了 AOB 种群的增加，从而加速了硝化作用和土壤酸化。培养结束时，与添加 150、300 和 400 mg/kg 尿素-N 处理的最大 pH 值相比，江西赤红壤的 pH 值分别降低了 1.25、1.54 和 1.84 个单位；对于来自安徽的赤红壤，相应的数字分别为 0.95、1.25 和 1.69。然而，添加（NH4）2SO4 抑制了 AOB 种群的增加，从而抑制了硝化作用和土壤酸化。添加 300 和 400 mg/kg（NH4）2SO4-N 的处理土壤的 pH 值在培养过程中几乎保持不变。AOB 在酸性条件下的农田土壤硝化中起着重要作用。添加尿素刺激了 AOB 种群的增加，从而加速了硝化作用和土壤酸化；而添加（NH4）2SO4 抑制了 AOB 种群的增加，从而抑制了硝化作用。
