Effects of conversion to organic agricultural practices on soil biota

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-manure plots during the summer. Larger earthworm species were 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.

Infiltration as a tool for detecting soil changes due to cropping, tillage, and grazing livestock

“…In 1985, Werner (1988) found significant differences (p<0.05) in infiltration rates between corn plots in the cropping system treatments ( Figure 1) before significant differences in most other physical properties were detectable. The low-input cash-grain (LIP-CG) system had significantly higher infiltration than did the conventional (CONV) system on five of the six sampling dates, while the low-input animal (LIP-A) system was higher than the CONV only for the June and October measurements.…”

“…Ponded infiltration (falling head) measurements were made in 1985 as part of a soil fauna study on the plots (Werner, 1988;Werner and Dindal, 1990). Werner measured infiltration on the corn plots monthly from June through November 1985 using a 30-cm single-ring infiltrome-ter and recording the rate of decrease in water depth.…”

Colonization of hardwood and pine wood chips by mites (Acari), with particular reference to oribatid mites (Oribatida)

“…A biological indicator that signals the quality of soil environment is Oribatida to Actinedida ratio (Werner and Dindal 1990;Gulvik 2007). In general, the higher the ratio the more stable the soil environment and the higher the level of its succession.…”

A Pragmatic Study of Conventional and Alternative Farmers in Colorado

“…Results indicate that alternative farmers have positive attitudes toward natural fertilizers and alternative production methods, while conventional farmers believe that synthetic fertilizers and pesticides should be used. Such differences reflect the actual farm production techniques, since most conventional farmers rely on agrichemicals, while such inputs are excluded from organic and alternative production that instead draw from intensive forms of management such as rotations, composting, timing, and biological pest control (Reganold 1988;Werner and Dindal 1990). Farmers had differing opinions about individual responsibility and farm size, as alternative farmers believe that individuals should farm only as much land as they can personally care for.…”