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Nitrogen Transformations and Microbial Population Dynamics in Soil Amended with Fermentation Residue¹

ABSTRACT

To evaluate the fate of N in an agricultural soil treated with an N-rich industrial byproduct, fermentation residue was applied to Yalesville fine, sandy loam at a loading rate of 75 dry metric tons/ha, or 2,130 and 1,780 kg N/ha during 1975 and 1976, respectively. Treated and control plots were planted to soybeans (Glycine max L. Merr.) each year. The treated plots yielded 4,350 kg/ha of soybean grain compared with 3,600 kg/ha for the controls in 1975, and 4,100 kg/ha compared with 3,700 kg/ha in 1976. Yield enhancements attributable to fermentation residue application were significant (P = 0.05) each year despite the severe repression of nodulation on treated plants compared with controls.

During the growing season, NO₃^–-N accumulations >80 µg/g oven dry soil were observed in the top 5 cm of treated soil, compared with accumulations of 15 µg/g or less in the control. Further, elevated NO₃^‘-N levels were observed in the top 91 cm of treated soil throughout the fallow and growing seasons, when compared with control plots, suggesting that some of the applied N may have been transported to the water table as NO₃^–.

Populations of five physiological groups of microorganisms closely mirrored soil levels of NO₃^–-N and NH₄⁺-N in both experiments. Denitrifying bacteria reached population densities of 3.0 x 10⁹/g oven dry treated soil compared with a maximum of 6.8 x 10⁵/g for control soil during the growing season. Enhanced N transforming activity by microorganisms in soil receiving fermentation residue compared with the control soil was supported by the elevated populations of NH₄⁺ and NO₂^– oxidizing bacteria, and NO₃^– reducing-, denitrifying-, and heterotrophic aerobic bacteria observed throughout the fallow and growing seasons. Although application of fermentation residue significantly increased soybean yields, the limited recovery of added N by the crop and the likelihood of substantial N losses suggest a reassessment of application rates or efforts to stabilize N applied to soils from fermentation residues.

Key Words: denitrification • leaching • nitrate reduction • denitrifying bacteria • nodulation • soybean nutrition

¹ Contribution from The Connecticut Agric. Exp. Stn., New Haven, CT 06504, and Agric. Res., SEA-USDA, St. Paul, MN 55108.

² Former Assistant Plant Physiologist, Dep. of Ecology and Climatology, The Connecticut Agric. Exp. Stn.; presently Associate Sanitary Microbiologist, Sanitation and Radiation Lab., State of California Dep. of Health, 2151 Berkeley Way, Berkeley, CA 94704.

³ Former Plant Physiologist, Dep. of Ecology and Climatology, The Connecticut Agric. Exp. Stn.; presently Plant Physiologist, USDA-SEA, AR, 1509 Gortner Ave., St. Paul, MN 55108.

Received for publication May 1, 1978.