The behavior of CO2 production, urease, phosphatase, and protease activities, amino acids, amino sugars, bacteria, and fungi was investigated during the microbial growth after the addition of a glucose-sodium nitrate solution to a red earth soil. The peak of the CO2 evolution rate preceded all other tested biochemical and microbiological criteria. Urease and phosphatase activities were significantly correlated with bacterial but not with fungal biomass. All other biochemical criteria tested did not show a correlation, on normal regression analysis, with biomass. Fungal growth occurred both in the glucose-amended soil and in the control. The temporal sequence observed among the tested enzymes was due to their different roles in the soil metabolism of glucose, as well as to their different cellular locations. The newly synthesized, acid-soluble, amino acids nitrogen and protease activity were short lived. Yet, some sort of stabilization for urease and phosphatase activities occurred. The changes in total amino acids nitrogen were due to behaviors of neutral and acidic amino acids. Of the amino acids tested, lysine, histidine, arginine, valine, isoleucine, leucine, and phenylalanine showed negligible differences among values of corresponding soil samples moistened with glucosenitrate solution and with distilled water.
The results show that no one measurement of activity is sufficient to interpret microbial growth in the soil system. Each of the indices measured must be used in conjunction with other tests to have a complete picture of the system.