Separation of soil Organic Debris using Sucrose-ZnCl2 Density Gradient Centrifugation

The active fraction of soil organic matter, which includes organic debris and light organic fraction, plays a major role in nutrient cycling. In addition, particulate organic matter is a valuable index of labile soil organic matter and can reflect differences in various soil behaviors. Since soil organic matter bound to soil mineral particles has its density lower than soil minerals, we partitioned soil organic matter into debris (< 1.5 g cm-3), light fraction (1.5-2.0 g cm-3), and heavy fraction (> 2.0 g cm-3), based on high density ZnCl2- sucrose solutions. Generally, partitioned organic bands were clearly separated, demonstrating that the ZnCl2- sucrose solutions are useful for such a density gradient centrifugation. The available gradient ranges from 1.2 to 2.0 g cm-3. Although there was not a statistically meaningful difference in organic debris and organomineral fractions among the examined soils, there was a general trend that a higher content of organic debris resulted in a higher proportion of light organomineral fraction. In addition, high clay content was associated with increased fraction of light organomineals. Partitioning of soil organic carbon revealed that carbon content is reduced in the heavy fraction than in the light fraction, reflecting that the light fraction contains more fresh and abundant carbon than the passive resistant fraction. It was also found that carbon contents in the overall organic matter, debris, light fraction, and heavy fractions may differ considerably in response to different farming practices