The Effect of Carbon Mineralization on Denitrification Kinetics in Mineral and Organic Soils1
- K. R. Reddy,
- P. S. C. Rao and
- R. E. Jessup2
Rates of denitrification and organic carbon (C) mineralization were measured simultaneously in soil suspensions maintained at 30°C under anoxic conditions. Nine mineral and seven organic soils were used in the study. Disappearance of NO-3 and production of CO2 were measured at various times during the 12-day incubation. Labeled NO-3 was used to differentiate denitrification from immobilization and reduction to NH4-N.
The rate of organic C mineralization followed first-order kinetics in all soils with the mineralization rate coefficient (kc) values varying from 0.075 to 0.405 day-1. The denitrification rates in anaerobic soils were shown to be proportional to the concentration of the two substrates: NO-3 and available C. The denitrification rate coefficient (kn) value was essentially constant for the mineral soils [0.00147 ± 25% day-1 (µg C/ml)-1], while kn values for the organic soils were somewhat more variable [0.00155 ± 65% day-1 (µg C/ml)-1].
Significant correlations were observed between NO-3 consumption and CO2 production. The molar ratio of NO-3 consumption to CO2 production ranged from 0.6 to 1.8. Significant relationships were also observed between water-soluble C (WSC) and total organic C (TOC), maximum available C (Cmax), and WSC and Cmax, respectively. Water-soluble C represented 0.4 to 0.9% of TOC, while Cmax represented about 0.6 to 1.4% of TOC. Results also showed that denitrification rates were influenced by the rate at which available C is mineralized and made available to the organisms.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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