Advanced understanding of SOC still requires further studies on diverse soils including a wide spectrum of paddy soils and agricultural practices. The objectives of this study were to investigate the effects of long-term fertilization on both light fraction (LF) and heavy fraction (HF) of soil organic matter and the relationships among total C, C/N ratio, clay content, and fertilization type in paddy soils. Compost application led to a significant increase in HF and consequently in C and N contents. Compost plots had a higher C/N ratio compared to those of treatments without compost in HF as well as LF. Correlation of C/N ratio to LF and HF was clearly separated into two groups as a boundary of about 9.5 of C/N ratio. These results clearly show that balanced fertilization together with composting could lead to synergic effects on enhancing C sequestration as well as plant nutrition in plow layer of paddy soils in Korea.

Ordination has been recognized useful method to analyze the effects of multiple environmental factors on dozens of species in vegetation ecology because of summarizing community data by producing a low-dimensional graphics. Main objective of this study was the application of ordination method, especially principal components analysis (PCA), to analyze the soil characterization on paddy treated by different green manure crops and tillage methods. Treatments included the three tillage treatments and two green manure crops as the following; (ⅰ) moldrotary + rotary tillage without green manure crop (Con), with (ⅱ) hairy vetch (ConHv), and (ⅲ) hairy vetch + green barely (ConHvGb), (ⅳ) rotary tillage without green manure crop (Rot), with (ⅴ) hairy vetch (RotHv), and (ⅵ) hairy vetch + green barly (RotHvGb), and (ⅶ) no-tillage (Notill). Vectorial distance result from PCA of soil properties including physical, chemical, and microbial properties showed the two main difference. Firstly, soil properties among plots without green manure were strongly affected by tillage strength [Vectorial distance: Con-Notil (5.88) 〉Rot-Notill (4.58)] at PC1 (35.0%) axis. But it was difficult to find the fixed trend among plots when green manure crop was added in plot. Nevertheless, two groups were separated by adding green manure crop at PC2 (29.2%) axis. These results show that PCA ordination methods could be used the research for change of soil characterization.