No favorable effect of reduced tillage on microbial community diversity in a silty loam soil (Belgium)

Among the soil management practices used to promote sustainable agriculture, reduced tillage and
retention of residues from the previous crop are reported to enhance significantly both soil fertility and
crop productivity. Here, high-throughput sequencing (454 technology) was used to see how the tillage
regime (conventional vs. reduced tillage) and the fate of crop residues (retention or removal) affect
microbial communities at two sampling depths (top soil: 0–5 cm and deeper soil: 15–20 cm) in a fertile
silty loam soil in Belgium. All combinations of these three factors were studied. After 6 years of
conversion from conventional to reduced tillage, depth emerged as the main factor responsible for
variation in microbial diversity, tillage regime ranked second, and
finally, crop residue fate had no influence
on microbial diversity. For both bacteria and fungi, the diversity appeared higher in the top soil than in
the deeper soil, and surprisingly, higher under conventional than under reduced tillage. These differences
are explained by changes in community composition due to taxon loss rather than taxon replacement.
The specific local set of environmental conditions (a loess-derived soil and an oceanic temperate climate)
may explain these results. These observations raise the question: does impoverishment in indicator taxa
influence soil processes, and thus crop production? To answer this question, we discuss how the presence
of certain indicator taxa liable to play an ecological role might relate to crop productivity.