EFFECT OF WATER-FILLED PORE-SPACE ON CARBON-DIOXIDE AND NITROUS-OXIDE PRODUCTION IN TILLED AND NONTILLED SOILS

The percentage of soil pore space filled with water (percent water-rilled pores, % WFP), as determined by water content and total porosity, appears to be closely related to soil microbial activity under different tillage regimes. Soil incubated in the laboratory at 60% WFP supported maimum aerobic microbial activity as determined by CO//2 production and O//2 uptake. in the field, % WFP of surface no-tillage soils (0-75 mm) at four U. S. locations averaged 62% at time of sampling, whereas that for plow soils was 44%. This difference in % WFP was reflected in 3. 4 and 9. 4 times greater CO//2 and N//2O production, respectively, from surface no-tillage soils over a 24-h period as compared to plowed soils.