Soil, Soil Life, Soil Layers:
http://school.discovery.com/schooladventures/soil/
http://www.brainyencyclopedia.com/encyclopedia/s/so/soil_life.html#Bacteria
Herbicides:
http://www.kids.net.au/encyclopedia/?p=he/Herbicide
Over tilling:
http://www.cals.ncsu.edu/sustainable/peet/tillage/tillage.html
Fungus:
http://interactive.usask.ca/ski/agriculture/soils/soilliv/soilliv_micfl.html
(you can find many links from this site) http://www.42explore.com/dirt.htm
Microorganisms:
http://www.ucc.ie/ucc/research/biomerit/agri2f.html
Green Manure and Cover Crops:
http://www.attra.org/attra-pub/covercrop.html
Conservation Tillige:
http://www.cals.ncsu.edu/sustainable/peet/tillage/tillage.html
http://ucanr.org/externalstories/ct.shtml
Grasslands:
http://www.factmonster.com/ipka/A0769052.html
All Topics:
(you can find many links from this site)
http://managingwholes.com/_eco-soil.htm
Ranching:
http://www.apnm.org/waste_of_west/