EFFECT OF TEMPERATURE ON SOIL MICROBIAL BIOMASS AND ITS METABOLIC QUOTIENT IN-SITU UNDER DIFFERENT TILLAGE SYSTEMS

Variations in the microbial biomass and the in situ metabolic quotient (qCO(2)) due to climatic conditions were determined in a typical soil from the Argentine Rolling Pampa. Microbial C was evaluated by fumiga tion - incubation and qCO(2) was calculated using soil respiration in the field. An inverse relationship between microbial C and soil temper ature was fitted to a model (r(2) = 0.90, P = 0.01). No significant as sociation with the soil water content was detected because the soil wa s generally near field capacity and thus water availability did not li mited microbial growth and activity. Values of qCO(2) increased (r(2) = 0.89, P = 0.01) as the result of metabolic activation, likely induce d by a higher maintenance energy requirement at high temperatures. The highest values of qCO(2) were obtained when microbial C was the lowes t, which was attributed to self consumption of microbial C in the pres ence of high temperatures. Consequently, microbial C was generally hig her (P = 0.05) in winter than in summer. Therefore, when microbial C i s used as an index of soil biological activity, the influence of tempe rature should be taken into account.