Healthy soil requires a wealthy diversity of microorganisms. Very little is known about how long-term agricultural land management affects the composition and genetic diversity of bacteria and fungi in soil. We know that forage, natural fertilizer applications, and cattle grazing increases the diversity of soil microorganisms and that conventionally tilled cropland with inorganic fertilizer results in a low diversity of soil microbes.
Conservation agricultural systems with wise use of animal manure is known to improve soil quality by increasing the number and type of soil microorganisms. Soil bacteria play a fundamental role in a vast array of ecological processes.
So if the diversity of soil bacteria in soils is reduced through stress these stresses could lead to a collapse of the soils ecosystems – and therefore to a consequent lack of productivity. It may not be leaching, erosion and runoff that are the primary culprits in worldwide soil fertility declines.
Even if there seem to be abundant “nutrients” to support vegetation, without the nutrient cycling and interaction with plant roots and other soil species (fungi, bacteria, nematodes, algae, yeasts, protozoa, turbellarians, tardigrades and rotifers...) the plants cannot thrive.
There was an interesting experiment done in November 2000 by the FAO.
Within a year, the aggregate structure of the pasture sample had been completely restored to levels typical of native forests, while the "orphaned" block of forest soil had become compacted and had lost most of its porosity.
What did they conclude made the difference? Soil organisms. The forest earth was rich in "ecosystem engineers" - earthworms, termites, millipedes and ants. The native macro-faunal communities in the pasture land had been all but lost. What does this teach us?
Soil biodiversity plays an enormous role in sustainable agriculture.