User:Mstreyn/sandbox

Impact of Tillage on Invertebrates
Tillage systems dramatically affect ecological niches. Therefore, the shift from intensive to conservation tillage in the US has the potential to dramatically alter abundance and diversity of invertebrates (e.g., earthworm, arthropods, nematodes) found in crop fields. It should be understood that this paper just touches the surface as far as the impact of tillage on invertebrates goes. Additional research should be considered when evaluating the impact of tillage on invertebrates.

Earthworms
Earthworm burrowing activities promote increased pore space and water infiltration. Tillage disturbs earthworm tunnels making it more difficult for them to maneuver through the soil and moving discs also have the potential to cut and kill earthworms. Because tillage increases compaction and soil temperature (due to less reflective material on the surface), a soil may become too dry and tight to maintain large earthworm populations. For example, Bostrom (1995) found in south-central Sweden that intensive plowing led to earthworm death rates between 73 and 77% in a mollic gleysol soil; however, earthworm numbers and biomass in these tilled plots shifted back to the levels of undisturbed plots after only 12 months. This recovery was attributed to the increased availability of organic matter and cocoons being redistributed in the soil from plowing.

A severe drought occurred during a study conducted at Horseshoe Bend near Athens, Georgia. Rainfall was 60% below the 100-year average and soil moisture content in the top 5 cm of no-till plots dropped from 18% in January to 6% in May. This led to a sharp decrease in earthworm populations in April in both no-till and conventional tillage systems. After the drought ended, however, the earthworm populations and biomass returned to almost predrought standings in the no-till system. The conventional plots, on the other hand, did not recover by the end of the study.

Arthropods
Soil arthropods include spiders, caterpillars, grubs, and beetles. They are affected by soil disturbances in 3 basic ways :

Stinner and House (1990) observed that no-till conditions in Georgia encouraged more diverse populations of arthropods. Their results demonstrated that no-till conditions promoted a more desirable environment for weed establishment and growth, offering a variety of food sources and shelter to enhance arthropod diversity. After examining arthropod communities for over 20 years in Ohio, Stinner and House (1990) found greater black cutworm damage in no-till than in tilled management systems. Barney and Pass (1987) compared arthropod populations in tilled and no-tilled alfalfa fields in Kentucky. Densities of the alfalfa weevils and aphids did not differ between tillage systems, while the potato leafhopper (one of the most influential pests of alfalfa in Kentucky), were reduced in numbers in the no-till system. Stinner and House (1990) speculated that the reduced potato leafhopper populations observed by Barney and Pass (1987) resulted from decreased host availability in alfalfa/grass mixtures and more natural predators in the no-till environment.
 * 1) Mechanical disturbances
 * 2) Residue placement
 * 3) Weed communities

Nematodes
The impact of tillage systems on nematode populations is not consistent. For example, Baird and Bernard (1984) found that tillage had a negligible impact on nematode communities including plant parasitic, bacteriovorous, fungivorous, and dorylaimida nematode species. McSorley and Gallaher (1994) also found that tillage did not have an effect on root knot nematode and stubby-root nematode in a Florida study. However, they found that lesion nematodes had higher populations in the conventional tilled plots versus the no-tilled plots.