http://www.organic.com/Non.profits/F2F/Features/earthworm.soil.html -- Lawrence F. London, Jr. mailto:london@sunSITE.unc.edu http://sunSITE.unc.edu/InterGardenTitle: Building Your Soil
The earthworm has all but been forgotten in modern agriculture. Many common practices like frequent tillage, fertilizing with anhydrous ammonia, heavy pesticide use, and weed-free farming have led to its demise. So much of what the earthworm used to do for free, we now have to do with tractors and chemicals. Here is a summary of some of the many benefits derived from healthy earthworm populations, along with a list of suggestions and a few tips on what you can do to bring them back
They improve the soil mix by helping it achieve the proper air, water, and solids ratio for maximum plant growth. Without them, we find it necessary to continually rip, disc, and springtooth the ground. Unknowingly, we further compact the soil while trying to "uncompact" it.
Its maze of tunnels increases the soils ability to absorb water. Without their activity, we are left to apply expensive materials to improve permeability, such as gypsum or some form of calcium. While these are good materials to apply to most soils and can do much good, they would be much less necessary if earthworms were present.
Analysis of earthworm castings, or earthworm manure, shows that the soil that comes out of the back end of an earthworm is closer to a neutral pH (7) than what goes in the front end, regardless of whether the existing soil is above or below pH (7). This is achieved by the action of the worms calciferous gland and the buffering action of carbonic acid. Think of all the limestone applications we have had to make to do what the earthworm used to do naturally.
Soil which has passed through the gut of an earthworm shows much more available phosphorus and potassium than the same soil which has not passed through the worm. Without the worms, you might as well enter your chemical supplier's phone number into your phone's memory for rapid dialing.
Free living nitrogen fixing bacteria are more numerous around the sides of the earthworm burrows. The mucous lining of the burrows are excellent sources of nutrients and ideal rooting environments. By contrast, we must till and fertilize to create good root growth. While tilling to create looser soil for easier root growth, we destroy many roots and root hairs.
The activity of the earthworm gut is like a miniature composting tube that mixes, conditions, and inoculates plant residues. The earthworm removes plant litter from the soil surface, turning it into free manure. Farms without many earthworms must buy more off-farm fertilizers and often end up buying compost "starting" agents called field sprays, which are wholly unnecessary in soils with high earthworm counts.
As yet, the exact reasons are unclear, but soil with earthworms invariably has less parasitic nematodes than soil without earthworms. Earthworms are the best indicator yet of healthy soils. Good soils contain a wide range of beneficial organisms which are directly stimulated by the activities of earthworms. These organisms trap, strangle, eat, and simply crowd out the plant-eating nematodes. By contrast, soils without earthworms and a healthy microbiology must be fumigated prior to planting. This fumigation kills both good and bad organisms indiscriminately. While fumigation may guarantee a "clean" start for a young plant, its protective action is fairly short-lived. When the nematodes return, and they always do, there will be little there to deter their proliferation.
Check your soils to see how well they are doing. If your soils don't have high earthworm counts, begin to encourage their return by:
Earthworm activities are deeply affected by cultivation, pesticide and fertilizer applications and by cultural practices. Ploughing decreases the abundance of earthworm communities. A study in England found that after 25 years of cultivation, earthworm populations decreased by roughly 85 percent. It was found that each cultivation killed approximately one percent of the population. But this was deep ploughing. Light cultivation had little direct effect on populations. However, one indirect effect of any form of cultivation is increased soil compaction, which does adversely affect earthworms. Although the top five inches of ground has been loosened, below is ploughpan which hardens with each repeated pass.
The negative effects of cultivation can be offset by the use of cover crops and organic fertilizers. These practices improve the microclimatic condition in the topsoil and provide nutritive resources. The effects of inorganic fertilizers on earthworms is variable. We do know, however, that fertilizers such as ammonium sulfate can be damaging because they increasing soil acidity. In some incidences, whole populations have been wiped out. Liming acid soils generally increases earthworm populations.
The effects of pesticides on earthworm populations are just as variable. Organochlorides, such as Chlordane, certain organophosphates, and carbamates are especially harmful. On the other hand, most herbicides seem to be harmless, except where their use has greatly decreased the worm's food supply.
When considering earthworms, you may want to think of the things that the $500 per acre fumigation doesn't provide: No improved mineral content, no improved permeability, no improved beneficial organism count, and no improved fertility. On top of that, it kills all your earthworms.
Earthworms are always working to make the soil better, not only for their own survival and reproduction, but also for the healthy survival of their primary food source, the residues from your crops. Earthworms are truly the farmer's best friend. And one last added benefit: they provide free fishing bait.