Slow recovery of soil biodiversity in sandy loam soils of Georgia after 25 years of no-tillage management

There is little data on the time required for recovery of soil species richness from disturbance such as tillage. We identified commercial no-till fields that represented a chronosequence of 4-25 years of reduced disturbance at the start of the study. These were compared to adjacent fields in conventional tillage as regularly disturbed reference sites. Five cotton fields in southern Georgia sandy loam soils were sampled four times over 2 years to determine the abundance of soil organisms at each site. Our results show an increase in organic matter content, profile stratification, and diversity of morphotypes within samples, with age in no-tillage management. Some groups of organisms responded more quickly to the no-till management, while most increase in diversity over several years. However, abundance values for each taxonomic category was not always significant. We also identified a pattern between our Spring and Fall samples for microbial biomass, organic carbon content and certain categories of organisms. During the first 8 years of no-tillage there was some increase in the abundance of organisms, but only the two older fields (8-26 years) had accumulated both abundance and species richness that approached that of undisturbed sites. Our results point to a greater importance of species diversity estimates in samples, compared to abundance estimates for taxonomic categories. We recommend that soil management studies in agro-ecosystems be conducted long enough to allow time for the changes in the below-ground community structure and its species diversity to occur. (c) 2005 Elsevier B.V. All rights reserved.