OBSERVATIONS ON THE METABOLIC ACTIVITY OF THE SOIL MICROFLORA

Abstract

The metabolic activity of the soil microflora has been studied manometrically with intact soil at optimum moisture and in the presence of various substrates. It was found that casamino acids were oxidized rapidly after a preliminary lag period. Oxygen uptake with this substrate showed no marked variation when the moisture level of the soil was between 60 and 80% of its moisture holding capacity. Mixtures of various non-nitrogenous substrates such as hexoses, pentoses, disaccharides, and organic acids yielded variable results. Uptake of oxygen by the soil in the presence of casamino acids was completely inhibited by dinitrophenol and azide. A marked decrease in respiratory activity in the soil was observed also when the reaction was lowered to pH 3.5 and 4.5. Considerable variation in gas exchange was obtained with soils which varied widely in fertility, organic matter, and nitrogen content.