Evaluation of Changes in CEC During Composting

Abstract

Changes in cation exchange capacity (CEC) during composting were evaluated with respect to compost amending, and compost processing. CEC_dm (CEC on dry matter basis), CEC_om (CEC on organic matter basis), and CEC_C (CEC on carbon basis) are parameters used for describing properties of composts. In this study effective cation exchange capacity (ECEC) was determined during drum composting; sampling from the infeed (FM) and the outfeed (DC0), and during curing in experimental heaps; sampling when the compost was turned first time (DC1), second time (DC2), and third time (DC3). The ECEC_dm was 18.1 (cmol+/kg) in FM, 35.5 in DC0 and 70.5 in DC3; this rise in ECEC_dm being beneficial from compost amendment standpoint. The ECEC_om was 20.6 (cmol+/kg) in FM, 41.5 in DCO and 89.8 in DC3, whereas ECEC_C was 39.3 (cmol+/kg) in FM, 77.2 in DCO and 183.1 in DC3. When ECEC was expressed on carbon mole basis (ECEC_molC), it was c. 0.5 (cmol+/Cmol) in FM, c. 0.9 in DC0 and c. 2.2 in DC3. These changes in ECEC_om, ECEC_C and ECEC_molC are valuable from the compost quality standpoint. Because the basis of CECdm, as well as, of CEC_om and CEC_C, is affected by composting, they can not be used in determining the effects of composting on the actual number of CEC sites. The amount of ash is not affected by composting, and thus ash basis can be used for determining the effects of composting on the actual number of cation sites. It was shown in this study, that during composting of manure the actual number of effective cation exchange sites increased from DC1 to DC3 by 34 percent, whereas at the same time ECEC_dm, ECEC_om and ECEC_C increased by 99 percent, 116 percent, and 137 percent, respectively. Based on CEC data reported in this paper and in compost literature, it was concluded, that changes in the number of CEC sites due to composting is overemphasized, when unanchored CEC_dm, CEC_om or CEC_C is used.