Influence of loss-on-ignition temperature and heating time on ash content of compost and manure

Loss-on-ignition (LOT) is a simple method for determining ash content, and by reciprocation, organic matter content of compost and manure. However, reported ignition temperatures and heating times for LOT measurements vary widely, and this brings into question the accuracy of one specific combination of ignition temperature and heating time over another. This study examined the effect of 42 temperature-heating time combinations (six ignition temperatures from 400 to 650 degrees C in 50 degrees C increments by seven heating times of 1, 2, 8, 12, 16, 20, and 24-h) on the ash content of a finished compost and a fresh manure. The experiment included the 550 degrees C for 2-h method recommended in Test Methods for Evaluation of Compost and Composting. The magnitude of the decrease in ash content due to increase in temperature was not consistent across all heating times. For example, after a 1-h heating time for ash content was 75.7% at 400 degrees C and 67.5% at 650 degrees C, compared to 69.6% at 400 degrees C and 66.8% at 650 degrees C after 24-h. Irrespective of heating time, an ignition temperature of 400 degrees C overestimated ash content for both compost and manure compared to the TMECC method. The TMECC method with its moderate temperature and short heating time requirement could reduce energy costs without affecting ash content results.