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 (Zen mays) a groecosystems in which earthworm populations were manipulated. Soil sa mples were collected on eight dates from May 1993 to April 1994. The s oil was dispersed and then sieved to separate the organic matter into the five size classes. The organic matter content of the whole, unsiev ed soil and the material retained on sieves was determined by mass los s on ignition. The unmanipulated and addition earthworm treatments wer e 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 wer e noted for the 0.053-0.25, 2-6 and > 6 mm SOM. The reduced EW treatme nt had higher 0.053-0.25 mm SOM only in May just prior to spring amend ment addition. Fertility treatment effects were not significant overal l except for an increased amount in the > 6 mm SOM for the manure trea tment. There were significant date effects for all SOM size classes wi th increases at the times of spring amendment and residue incorporatio n and fall root senescence followed by rapid declines. (C) 1997 Elsevi er Science Ltd.