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Stimulation of Soil Respiration by Volatiles from Alfalfa¹

ABSTRACT

Volatile compounds obtained by distillation of a water slurry of alfalfa hay increased the respiration rates of 12 soils three- to eight-fold. The active volatiles are neutral organic compounds that rapidly penetrate the soil and cause an immediate increase in soil respiration. The intensity of the respiration enhancement is directly related to the relative concentration of the volatiles. Low RQ values of soil during exposure indicated the microflora utilized substrates low in oxygen. The optimal temperature for respiration enhancement of treated soil was 36C. The duration and magnitude of the soil respiration response were dependent on the volume of distillate used. The optimal volume maintained the increased respiration rate for 72 hours. Larger volumes reduced the duration of response to 2 hours, suggesting toxicity of the volatiles at higher concentrations.

¹ Contribution from the US Soils Laboratory, Soil and Water Conservation Research Division, ARS, USDA, Beltsville, Md.

² Research Soil Scientist and Soil Scientist (Research Assistant), respectively.

Received for publication July 15, 1968. Accepted for publication December 5, 1968.