Partitioning of organic matter in soils: effects of pH and water/soil ratio

The effects of pH and water/soil ratio on the soil–water partitioning of soil organic matter (SOM) in 15 New Jersey soils were investigated. The dissolved organic carbon (DOC) concentration stabilized within 24 h. An increase in pH increased dissolution of soil organic matter. The ratio of UV absorbance at 465 nm to that at 665 nm (E4/E6 ratio) of the dissolved organic matter decreased with increasing pH, indicating a greater fraction of high molecular weight of SOM being released into solution phase at higher pH values. A similar result was suggested by decreases in the fulvic/humic acid ratio with increasing pH. At a fixed pH, the partition coefficient (Kd) of SOM correlated with soil CEC. Normalization of Kd with CEC resulted in a linear correlation between the normalized Kd with pH.