Submitted to: American Society of Agronomy Meetings
Publication Type: Abstract Only
Publication Acceptance Date: October 25, 2001
Publication Date: October 25, 2001
Citation: Cambardella, C.A. 2001. Early season changes in biologically-active SOM [abstract]. American Society of Agronomy Meetings. s03-cambardella140635-P.pdf. Technical Abstract: Changes in biologically-active SOM (ba-SOM)can be a useful indicator of longer-term changes in total SOM. My objective was to quantify intra-seasonal changes in ba-SOM for 3 field sites (Site 1 and 2 in N central and site 3 in NE IA). All sites were under no-till management and were cropped to corn and soybeans. Surface soil (15 cm) samples were collected at several points across the growing season during 1995, 1996 and 1997 for all 3 sites. Early-season changes were monitored at site 1 every 2 weeks from mid-March to mid-June in 1999. POM C and N increased over-winter by more than two-fold for all 3 field sites. Under soybean, about 50% of POM C and N present in early spring was lost by November. Under corn, POM N loss was similar to that under soybean, but POM C was essentially equal in May and November. Between March 18 and June 9, most of the total POM C loss was from the large POM subfraction. N loss occurred in the small POM subfractions, with early losses occurring in the heavy subfraction and later losses in the light subfraction. Data from all 3 field sites for all years showed POM and N were lost across the growing season and replenished over-winter, presumably from the decomposition of roots. Losses of POM C and N were decoupled across the growing season, suggesting that different mechanisms may be involved in POM C and N loss. The retention of POM C under corn may contribute to corn's relative high C storage potential.