Temporal Variability of Microbial Populations and Enzyme Activities of No-tillage Soils in Argentina

Abstract

Work in temperate regions has shown that long-term no-tillage (NT) affects microbiological and biochemical properties of soils. However, relatively little research has been done on this in South America or on early microbial responses after converting to NT. Enzyme activities respond to NT but information is needed on how these assays are related to the microbial populations. The goal of this research was to study temporal dynamics of microbiological and enzyme properties of soils (0–10 cm depth) under NT systems at three on-farm sites located in the primary agricultural region of Argentina. The study had a split plot design with two main plot (medium-term) treatments of years under NT (1–3 or 4–7 years) and a subplot (season) treatment of eight seasonal samplings (repeated measures) over a two-year period. Oligotrophic bacteria counts and dehydrogenase, catalase, phosphotriesterase and urease activities often showed seasonal affect with an increase over the two-year period within each range of NT years. However, seasonal variability was not closely related to seasonal climatic patterns. Urease activity had the highest variation within seasons. Soils after 4–7 years NT had 14% greater heterotrophic bacteria counts (P < 0.05) than soils after 1–3 years of NT. Ureolytic bacteria and filamentous fungi populations, and microbial biomass C were relatively stable in both the seasonal and medium-term NT periods. Of the physical and chemical properties, only soil water content had significant correlations with the microbiological properties (r = 0.52 to 0.77, P < 0.001). The results suggest that NT was improving soil biological as most properties were increasing over the years (P > 0.05) and that these changes were maintained over short-term seasonal sampling periods.