Organic matter dynamics in maize agroecosystems as affected by earthworm manipulations and fertility source

We quantified the mass of five size classes (>6, 2–6, 0.25–2, 0.053–0.25 and <0.053 mm) of soil organic matter (SOM) in maize (Zea mays) agroecosystems in which earthworm populations were manipulated. Soil samples were collected on eight dates from May 1993 to April 1994. The soil was dispersed and then sieved to separate the organic matter into the five size classes. The organic matter content of the whole, unsieved soil and the material retained on sieves was determined by mass loss on ignition. The unmanipulated and addition earthworm treatments were combined as a class since they were not different for any SOM class. The reduced EW treatment had significantly higher total, 0.25–2 and <0.053 mm SOM (P < 0.05). No significant overall earthworm effects were noted for the 0.053–0.25, 2–6 and >6 mm SOM. The reduced EW treatment had higher 0.053–0.25 mm SOM only in May just prior to spring amendment addition. Fertility treatment effects were not significant overall except for an increased amount in the >6 mm SOM for the manure treatment. There were significant date effects for all SOM size classes with increases at the times of spring amendment and residue incorporation and fall root senescence followed by rapid declines.