Kinetic Responses of Soil Carbon Dioxide Emission to Increasing Urea Application Rate
2011
Lee, S.I., Bioenergy Crop Research Center, NICS, RDA, Muan, Republic of Korea | Lim, S.S., Chonnam National University, Gwangju, Republic of Korea | Lee, K.S., Chonnam National University, Gwangju, Republic of Korea | Kwak, J.H., Chonnam National University, Gwangju, Republic of Korea | Jung, J.W., Yeongsan River Environment Research Laboratory, Gwangju, Republic of Korea | Ro, H.M., Seoul National University, Seoul, Republic of Korea | Choi, W.J., Chonnam National University, Gwangju, Republic of Korea
BACKGROUND: Application of urea may increase CO₂ emission from soils due both to CO₂ generation from urea hydrolysis and fertilizer-induced decomposition of soil organic carbon (SOC). The objective of this study was to investigate the effects of increasing urea application on CO₂ emission from soil and mineralization kinetics of indigenous SOC. METHODS AND RESULTS: Emission of CO₂ from a soil amended with four different rates (0, 175, 350, and 700 mg N/kg soil) of urea was investigated in a laboratory incubation experiment for 110 days. Cumulative CO₂ emission (C∧cum) was linearly increased with urea application rate due primarily to the contribution of urea-C through hydrolysis to total CO₂ emission. First-order kinetics parameters (C∧0, mineralizable SOC pool size; k, mineralization rate) became greater with increasing urea application rate; C∧0 increased from 665.1 to 780.3 mg C/kg and k from 0.024 to 0.069 day-¹, determinately showing fertilizer-induced SOC mineralization. The relationship of C∧0 (non-linear) and k (linear) with urea-N application rate revealed different responses of C∧0 and k to increasing rate of fertilizer N. CONCLUSION(s): The relationship of mineralizable SOC pool size and mineralization rate with urea-N application rate suggested that increasing N fertilization may accelerate decomposition of readily decomposable SOC; however, it may not always stimulate decomposition of non-readily decomposable SOC that is protected from microbial decomposition.
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