Submitted to: Agronomy Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: 8/1/1999
Publication Date: N/A
Technical Abstract: In the Pacific Northwest there is a growing concern for the loss of soil organic matter and a concomitant increasing interest in direct seeding techniques. Soil from several long-term tillage systems in Oregon and Washington was fractionated into particulate organic matter (POM) pools. Total soil C, POM C and POM supported respiration were determined and compared. The greatest amount of POM C was found in the 0-5 cm depth in direct seeding systems and a permanent pasture. In conventionally tilled systems, the distribution of POM C was more uniform over 20 cm. The POM C content was the least in management systems that incorporated residue burning and wheat - fallow crop rotation. Highest POM supported respiration rates were found in no-till and pasture management systems. Three or four definite changes in POM supported respiration rates were observed during incubation, suggesting kinetically discrete carbon pools. The POM supported respiration rates were significantly less that comparable whole soil respiration rates. These observations are consistent with the lack of aggregate stability normally found in Pacific northwest soils suggest that direct seed management systems are essential to maintain soil organic matter in the region.