EGU22-5503, updated on 27 Mar 2022
EGU General Assembly 2022
© Author(s) 2022. This work is distributed under
the Creative Commons Attribution 4.0 License.

Nitrogen fertilizers control CO2 emission from calcareous soils: implications for land management and global warming

Jingjing Tao1,2, Lichao Fan1, Jianbin Zhou2, Yakov Kuzyakov1, and Kazem Zamanian1
Jingjing Tao et al.
  • 1Soil Science of Temperate Ecosystems, University of Göttingen, Göttingen 37077, Germany
  • 2College of Natural Resources and Environment, Northwest A&F University/Key Laboratory of Plant Nutrition and the Agri-environment in Northwest China, MOA, Yangling 712100, Shaanxi, China

Soil acidification has increasingly become a critical issue for sustainable production due to the excessive nitrogen (N) fertilization in agricultural systems. Application of N fertilizers and the consequent nitrification yield protons (H+), which strongly and irreversibly accelerate dissolution of soil inorganic carbon (SIC) e.g., CaCO3, leading to CO2 release in the atmosphere. Here, 14C-labeled CaCO3 was added to calcareous soil (0.75% CaCO3) to investigate the effects of chicken manure, urea, NH4NO3, KNO3 and (NH4)2SO4 on soil acidification and to estimate the SIC contribution to CO2 emission. 250 mL gas-tight jars were filled with a cropland soil (pH = 7.2), homogenously mixed with 1.3% Ca14CO3 powder (14C activity = 11.3 kBq pot-1). Following fertilization in rates of 0.1, 0.15, 0.25 g N kg-1 soil, NaOH was applied to trap the emitted CO2 and to determine 14C activity. CaCO3 addition increased soil pH values by 0.17-0.43 units. Addition of ammonium-based fertilizers ((NH4)2SO4, NH4NO3) strongly decreased pH up to 0.3 units. All fertilizers increased CO2 emission (5.1%-180%) compared to the unfertilized soil after 44 days of incubation except KNO3. SIC-originated CO2 due to fertilization was ranged from 2.9 to 160 mg C kg-1 (1.1% to 48% of total emitted CO2). Manure and urea had lowest impacts on SIC-driven CO2 during the first 5 days (2.9-34 mg C kg-1) irrespective of the application rate. Thereafter, the effects of fertilizers on SIC-originated CO2 increased in the order: urea < manure < KNO3 < NH4NO3 < (NH4)2SO4. As nitrification of (NH4)2SO4 yields in 4 mol H+, which neutralizes 2 mol carbonates, it initially caused the highest SIC-originated CO2 until 9 days. Urea and NH4NO3 release by nitrification 2 mol H+ per mole of fertilizer, but urea initially hydrolyses to NH4OH, which increases soil pH. So, urea addition had the minimum SIC loss as CO2 in the first 5 days, but starting from 16th day, CO2 emission sharply increased and reached to highest values among the fertilizers. Manure increased SIC-originated CO2 emission from 23rd day of incubation. Gradual and incomplete mineralization of organic N of chicken manure duration 44 days explains the smallest released CO2 from CaCO3 and slowest acidification in the first 16 days. Furthermore, Ca2+ and Mg2+ in manure may be precipitated as carbonates, which decrease the SIC share in the emitted CO2. Generally, the higher the applied fertilizer amounts, the larger was the proportion of CO2 released from SIC. Both the fertilizer chemistry and the application rate played significant roles in dissolution of carbonates. Summarizing, the correct selection of the type and amount of fertilizers based on soil properties and plant demand is necessary to decrease SIC-originated CO2 emission to mitigate global warming, and also save various ecosystem services such as organic matter stability and increase C sequestration.

How to cite: Tao, J., Fan, L., Zhou, J., Kuzyakov, Y., and Zamanian, K.: Nitrogen fertilizers control CO2 emission from calcareous soils: implications for land management and global warming, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5503,, 2022.