Microbiological Indicators of Soil Quality and Degradation Following Conversion of Native Forests to Continuous Croplands

Background

This study was conducted in Gorgan City in the Golestan Province of Northeast Iran. The province has a moderate and humid climate known as the "moderate Caspian climate" and features broadleaf forests and adjacent cropland in a semi-arid climate system. This study focused on microbial functional capacity as an indicator of soil degradation and deforestation. The research investigated the relationship between soil organic carbon losses and soil enzyme activities following land use conversion from native forests to croplands. The main assumption is that the higher soil microbial enzyme activities or biomass would represent the better soil functionality of the site. The researchers hypothesize that the relationship between enzyme activities and soil organic carbon could provide an environmental indicator of assessing biochemical function of soils as a consequence of land use changes.

Research Goals & Methods

Composite soil samples were collected from the two different soil layers (0-20 cm and 20-40 cm) in two different land uses (n=3)—broadleaf forests and adjacent croplands. Soil microbial biomass carbon (SMBC) was determined by using the fumigation-incubation method, and the SMBC/ soil organic carbon (SOC) ration was measured from the results as well. From a laboratory incubation experiment, basal soil respiration, C mineralization, soil C turnover rate and the activities of five soil enzyme were obtained and calculated.

Conclusions & Takeaways

The results indicate that the content of SMBC and the absolute activities of most enzymes decreased with deforestation and continuous cultivation. However, the specific enzyme activities expressed per unit of SMBC had a tendency of positively related to C turnover rate, implying faster C cycle under deforestation. These results suggest the potential of soil enzyme as an indicator of SOC loss and soil degradation.