There are two main reasons for the contradictory results in

Fig. 7. Relationship between modeled soil CO2 emission and observed soil CO2 emission. Dashed line is the 1:1 line.Figure optionsDownload full-size imageDownload as PowerPoint slide
4. Discussions
4.1. Crop straw amendments and soil CO2 emissions
This study focuses on the conversion of forests to croplands and the possible effects of recycling plant residues on soil C evolution. The five straws used in this study did show various decomposition rates under normal agricultural practices (Fig. 2). However, other important factors than quality and amount of straw incorporated (such as frequent soil tillage, changes in plan rooting, other agricultural practices) may impact on soil C Busulfan and respiration (PEs would only affect the zone of straw incorporation). Therefore, it is necessary to comprehensively investigate the effects of agricultural practices (e.g., tillage) and PEs on soil CO2 emissions.
4.2. Implications for PEs
The amplitude of the native SOC decomposition response to external organic matter addition was very large (ranged from 95.1% inhibition to 1207% stimulation) (e.g., Zhang et al., 2013). Previous studies have suggested that positive PEs were induced due to microbial growth and the accompanying increased enzyme production. However, the possible mechanisms of negative PEs included the toxicity of the substrates to microorganisms (Kuzyakov et al., 2000, Fontaine et al., 2003, Kuzyakov, 2010 and Zhang et al., 2013).