Found an interesting study of which I pasted a section below. This is not meant to incite a riot but instead to provide interesting reading for those considering organic additions to their current service. A lot has been said, in the archives, about organic vs. inorganic fertilzers and pesticides but very little mention of the benefits and/or harm to the long term health of the organisms that already live there. It is a fascinating compilation of different studies. For the whole document go to : http://www.cityofseattle.net/util/lawncare/docs/Grnlwn61.pdf Here is a small segment that I found particularly interesting...... "Ecologically Sound Lawn Care for the Pacific Northwest Why Make A Change? 10 .......Earthworms and other soil invertebrates are essential to maintaining soil structure and recycling organic debris, such as thatch, back into nutrients available to the grass plant.85 86 87 Thousands of microorganism species (bacteria, fungi, and protozoa) form the food base for these invertebrates.a The microorganisms perform the essential first steps in nutrient recycling, and build soil structure at the microscopic level.88 89 They also compete with and (along with predacious invertebrates) prey upon the relatively few fungi and insects that cause pest problems in turfgrass.90 91 Several studies have identified negative side-effects of regular use of pesticides and soluble fertilizers on the health of this soil ecosystem, and on turfgrass vigor, drought hardiness, soil compaction, and thatch buildup. A study measuring acute toxicity to worms concluded that most pesticides were very toxic to extremely toxic (LC50 = 1-100 mg/cm2, which means that at that concentration half the earthworms died during a short experiment) and reported that the breakdown products of 2,4-D were more toxic than the original material. The soluble fertilizers that were tested, ammonium nitrate and methyl urea, had LC50s in the 100-1000 mg/cm2 range.92 Another study concluded that earthworm growth and reproduction is significantly reduced at much lower chemical concentrations than those that cause death.93 Several turfgrass trial studies with commonly used fungicides, insecticides and herbicides have reported large reductions in earthworm activity and a significant buildup of thatch layers, compared to untreated control plots.94 95 96 97 98 Another study reported that mechanical exclusion of earthworms (by mesh bags) prevented thatch breakdown, and concluded that earthworm activity provides benefits (such as soil incorporation into the thatch layer) that are comparable to topdressing with topsoil.99 A trial that simulated a high-maintenance (synthetic fertilizer, herbicides and insecticides) lawn care program for four years concluded that soil and thatch pH decreased significantly [soil became more acid] and thatch accumulation more than tripled under the high maintenance program compared to untreated control plots. Soluble nitrogen fertilization commonly results in soil acidification, which inhibits microbial activity and soil invertebrate populations.100 A seven-year trial of varying rates of ammonium nitrate fertilization on turf reported that soil acidity and thatch thickness increased, and earthworm and other invertebrate populations decreased, in direct proportion to increasingly high levels of nitrogen fertilization.101 Soil compaction, like thatch buildup, causes poor root development, lack of drought hardiness, and lack of vigor in grass plants.102 A trial on British sports fields where worms were killed with a strong insecticide reported that water infiltration rates fell 16% by six months after treatment, and fell 40% by twelve months after the worms were killed. This study concluded that The main cause of the reduction was a Dr. Elaine Ingham of Oregon State University notes, Earthworms do not make the enzymes to degrade organic matter they have the enzymes to digest bacteria and fungi and absorb the soluble nutrients that are released. Bacteria bind the smallest building blocks of soil into microaggregates. Fungi, and root hairs, bind the small building blocks into larger aggregates. Earthworms consume these aggregates, with the bacteria, fungi, root hairs, protozoa, nematodes and arthropods in them. Earthworms then build larger channels in soil, but the smaller aggregates and other organisms must be present for earthworms to survive in soil. blockage of the main conducting channels, as these large pore spaces were no longer being created by the earthworms.103 In a laboratory experiment, researchers concluded that the presence of earthworms greatly enhanced the growth of perennial ryegrass. Uptake of most major and trace elements by ryegrass was increased in the presence of earthworms. That study also concluded that earthworms reduced soil compaction and increased pore space in the root zone of the ryegrass plants.104 Most plants, including grasses, depend on webs of beneficial fungi, which grow in and around their root systems, to provide both nutrients from the soil and protection from disease-causing fungi.105 Several studies have concluded that these beneficial mycorrhizal fungi (root-fungi) are inhibited by fungicides, and also by high levels of fertilization.106 107 108 Resurgence of disease and insect problems is commonly reported after use of fungicides and insecticides, because of reductions in fungi and insects that compete with or prey upon the problem pests.109 Resistance to pesticides developed by both insects and fungal diseases is also commonly noted by turf scientists and professionals.110 The scientific literature reviewed here suggests that turf management techniques that support the diversity of life in the soil community, through proper cultural practices and through limiting the intensity and frequency of chemical applications, will yield healthier turf with less thatch and fewer soil compaction, disease, and insect problems."