Does moisture speed the process of decay? Does the presence of soil hasten the process?

Half-fill two glass jars with dry soil, and leave a third jar empty. Add equal amounts of leaves and grass cuttings to each of the three jars. Moisten the soil in one jar. Cover the jars.

After one week, compare the contents of the jars.

Under which conditions do the materials seem to be changing fastest into soil?

What accounts for the differences in the contents of the three jars?