Werner, M., and D. Dindhal. 1990. Effects of conversion to organic agricultural practices on soil biota. American Journal of Alternative Agriculture 5(1):24-32.
Abstract: In the fifth year of an agricultural conversion
experiment in Pennsylvania, we studied the soil biological community under
three treatment regimes planted with corn: organic-manure, organic-legume,
and a conventional system. The organic treatments consisted of complex
crop rotations, cultivations, and organic matter inputs to control pests
and maintain soil fertility. The conventional system consisted of a simple
corn/soybean rotation with synthetic fertilizer and pesticide inputs.
High rates of CO2 evolution (a measure of potential microbial activity)
in the organic plots corresponded with high levels of organic matter input.
Soil nematodes were most abundant in organic plots, although seasonal
patterns differed between the two organic treatments. Soil microarthropods
were dominated by fungivorous Prostigmata mites, which reached peak abundance
in organic plots two to five months after organic matter incorporation.
Oribatid mites, which were rare throughout the study, followed the same
pattern of abundance in each treatment and were probably most influenced
by tillage disturbances. Predatory Mesostigmata were generally more abundant
in organic plots. Surface-dwelling Collembola were abundant briefly in
the spring, but soil-dwelling species dominated numerically throughout
the cropping season. Spring tillage appeared to have a strong negative
effect on earthworm populations in all plots. Small earthworm species
became abundant in organic-legume and conventional plots after the autumn
harvest, when crop residues covered the undisturbed soil. The systems-level
nature of the Conversion Project experiment makes it difficult to identify
cause-effect relationships. The data do suggest that organic amendments
tend to enhance soil biological activity, while tillage disturbances tend
to disrupt the biotic community.