The effect of chemical fertilizer on soil organic carbon renewal and CO2 emission—a pot experiment with maize
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Background and Aims
Previous studies have clearly shown substantial increases of soil organic carbon (SOC) in agricultural soils of Yellow River reaches. Those soils did not receive organic fertilizer input, but did receive chemical fertilizer inputs. Thus, to investigate the hypothesis that the observed SOC increases were driven by chemical fertilizer additions, a maize pot experiment was conducted using a Fluvisol that developed under C3 vegetation in the Yellow River reaches.
Using the natural 13C abundance method we calculated the SOC renewal ratio (C renewal), and separated total soil organic carbon (TOC) into maize-derived soil organic carbon (SOCmaize) and original soil organic carbon (SOCoriginal). Carbon dioxide fluxes and microbial biomass carbon (MBC) were determined by closed chamber method and fumigation-extraction method, respectively. The experiment included five treatments: (1) NPK: application of chemical fertilizer NPK; (2) NP, application of chemical fertilizer NP; (3) PK: application of chemical fertilizer PK; (4) NK, application of chemical fertilizer NK; and (5) CK: unfertilized control.
Fertilization increased maize biomass (including grain, straw and root), TOC, C renewal, SOCmaize, maize-derived carbon (MDC: including SOCmaize, and root and stubble biomass carbon) and MBC, and these values among the treatments ranked NPK>NP>PK>NK>CK. The C renewal was 5.54–8.50% across the treatments. Fertilization also increased soil CO2 emission (including root respiration and SOCoriginal decomposition), while the SOCoriginal decomposition during the maize growing season only amounted to 74.0–93.4 and 33.5–46.1% of SOCmaize and MDC among the treatments, respectively. Thus input was larger than export, and led to SOC increase. Maize grain and straw biomass were positively and significantly correlated with soil δ13C, TOC, C renewal, SOCmaize, MDC and MBC.
The study suggests that chemical fertilizer application could increase C renewal by increasing crop-derived C and accelerating original SOC decomposition, and that as long as a certain level of crop yield or aboveground biomass can be achieved, application of chemical fertilizer alone can maintain or increase SOC level in Fluvisol in the Yellow River reaches.
KeywordsChemical fertilizer δ13C Carbon turnover Carbon sequestration Soil respiration
This work was financially supported by the National Natural Science Foundation of China (No.40621001) and the Knowledge Innovation Program of the Chinese Academy of Sciences (No. kzcx2-yw-q1-07, kzcx2-yw-312). We would like to thank Professors Yacheng Cao and Qiao Jiang for their technical assistance. We also thank three anonymous referees, section editor Johan Six and editor in chief Hans Lambers for their helpful comments and suggestions that improved the manuscript greatly.
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