PARENT SESSION
Symposium #5: Sustaining and restoring our soil.
Sponsored by ESA Soil Ecology Section
Organized by: S.M. Adl. and S. Morris.
Monday, August 6, 2001. 1:00 PM to 4:50 PM. Madison Ballroom A
Consequences of Long-term conservation practise in trophic structure of agro-ecosystems.
Adl, Sina1, Coleman, David1, 1
ABSTRACT- Agricultural fields become depleted of soil organic matter over time, as crop biomass is removed annually. Addition of artificial fertilisers, pesticides and herbicides impact the soil decomposer community, and agro-ecosystems are usually poor in species abundance and diversity. The additional impact of irrigation, mechanical compaction and tillage disruption contribute further to this process and the accompanying soil erosion. In order to manage the vast expanses of land under agriculture in more sustainable ways, we need to understand soil ecology in more detail. The aim is to obtain a balance between high sustainable yields, pest management and maintaining soil organic matter through sustainable management practise. The consequences of agricultural management (conventional tillage and no-till) on soil decomposer ecology has been monitored for over 15 years at the Horseshoe Bend site (Athens GA). Here we review these results and compare them to farmer cotton fields in southern Georgia, that have been in no-till conservation for 4 years to 25 years, and to control farm sites (in conventional tillage). Soil samples were assayed for total microbial biomass, and extracted for nematodes, microarthropods, testate and naked amoebae, ciliates and flagellates. Species were categorised into functional trophic groups based on known feeding habit. Fields under conservation management, in general, have more complex trophic structures, with more diverse species in functional groups. This complexity increases with number of years under conservation, and it is observable within five years. Fields under conservation management that were supplemented with composts show much greater and faster accumulation of decomposer food webs. Over time, the accumulation of soil organic matter horizons, the elaboration of decomposer food webs and the massive reduction in soil erosion are encouraging. Crop yields in these farmer fields have been comparable or better than adjacent fields under conventional management, particularly in the last three drought years.
KEY WORDS: agro-ecosystem, soil ecology, decomposition, conservation