No-till or no-dig gardening is a method of preserving the natural integrity of the soil. It preserves soil structure, promotes biological activity, and preserves soil fertility. All of this is compromised by cultivation. Here I will explore the 'Why' and 'How To' of No-Dig gardening.
(Editor's Note: This article was originally published on February 25, 2008. Your comments are welcome, but please be aware that authors of previously published articles may not be able to respond to your questions.)
"If we throw mother nature out the window, she comes back in the door with a pitchfork." Masanobu Fukuoka 
What is No-Dig Gardening?
Origins. The origin of no-dig gardening is sometimes attributed to Australian writer and conservationist, Esther Deans  who outlined a method of piling mulch over newspaper to prepare garden beds for planting. The mulch suppresses weeds, conditions the soil, and invites natural soil making processes. Others attribute the invention of no-dig gardening to Japanese Microbiologist, Masanobu Fukuoka who advocated a method of natural soil building in this book, The One-Straw Revolution . The Permaculture movement, a world-wide organization promoting natural gardening or no-dig techniques  embraces both Esther Deans and Masanobu Fukuoka's work.
In the United States origins are more apt to be attributed to Ruth Stout    who advocated fighting weeds by piling on a mulch of straw, pine straw, leaves, and compost. The thicker the mulch, the greater was the deterrent to weeds. Updated versions are Patricia Lanza's Lasagna Gardening  and Lee Reich's Weedless Gardening.  No-Dig garden writers are profiled in Shapiro and Harrisson's Gardening for the Future of the Earth. 
How To. Very little surface preparation is required to build a no dig garden, assuming of course that weedy shrubs and trees have been removed. A preliminary step could be to solarize [10a, 10b] the area to kill perennial weeds. The general method is to cut, flatten, or mow existing surface vegetation. Then, following a soaking rain or irrigation, the surface is covered with several thicknesses of wet newspaper (Deans) or cardboard.  After soaking again, a mulch of whatever organic materials are available is applied over the cardboard or newspaper foundation. Typically the mulch would include straw, shredded wood chips, leaves, shredded junk mail, kitchen scraps, coffee grounds, used tea leaves, animal manures, weeds, and used potting soil. According to the Lasagna Method , equal volumes of "greens" and browns" are layered over the cardboard. More technically, the aim is to get a carbon to nitrogen ratio of 30 to 1.  After a few weeks to allow the mulch to settle in, planting begins directly into the mulch. Alternatively, the mulch may be allowed to over winter in preparation for spring planting. A recent innovation is the use of living mulches where the crop is planted together with a cover crop selected to surpress weeds.  No-dig gardening, as opposed to double digging, rototilling, or other forms of cultivation is intended to eliminate weeds, thereby eliminating the need for cultivation.
Raised beds, container gardening, and strawbale gardening  are all relevant methods of no-dig gardening. Below (Figure 1) is a hedge of potato plants planted in whiskey barrels in a west coast of Alaska garden. The red potato Ididered has a pink blossom, but white and yellow potatoes have white blossoms (see Thumbnail). Figure (3) is a coastal Alaskan raised bed garden.
Fig. 1. Potato Barrels in an Alaska garden Fig. 2. Ididared Potato Blossom Figure 3. Raised beds in an Alaskan garden. Zone 3
Why. Cultivation disturbs soil life, causes soil compaction, exposes and depletes nutrients, and kills micro-organisms. The natural cohesion of soil particles is disturbed so that erosion is more likely. The broad spectrum nutrients lost to cultivation are usually replaced by only the essential nutrients in commercial fertilizers. Not-digging, on the other hand, preserves the natural integrity of the soil. Not-digging improves soil health, and also protects against erosion, improves both the quality of garden plants and the environment. Environmental quality is enhanced when soil nutrients stay within the soil rather than eroding into rivers and streams or exposed where they contribute to atmospheric greenhouse gases. Excessive fertilizers contaminate groundwater, rivers, and streams causing eutrophication - a condition of excessive nutrients  which can threaten the habitats of aquatic animals and wild life.
Soil integrity refers to its (1) biological constituents, (2) chemical characteristics or fertility, and (3) physical properties. The soil's biological components integrate the physical and chemical properties to produce over-all soil quality.
Soil Biology. Bacteria, fungi, and soil animals are the main biological performers in soil bioactivity.
Soil bacteria and fungi. One type of soil bacteria is rhizobia, which are used to inoculate legumes and convert nitrogen into a form that the plants can use. They are called "nitrogen fixers". By forming a symbiotic relationship with plants, the fungi mycorhizas extract carbohydrates from plant roots and transfer phosphorous to the root. The hyphae (threads) formed by some mycorhizae stabilize soil. Micorhizae may also participate in copper and zinc metabolism of plants. 
The rhizosphere. The most productive part of soil is the upper 20 to 30 cm, which is called the root zone or rooting zone. The rhizosphere is the particular community of relationships between plant roots, adjacent soil, and microbial activity. Each type of plant exudes a signature exudate of carbon compounds. These carbon compounds attract certain microbes within the soil. These bacteria or fungi then form a symbiotic relationship with the plant root. As soil creatures feed on the root compounds they produce fecal pellets which cycle nutrients making them more available to the plant. Or, the fecal pellets may combine with soil particles to form aggregates more favorable to root growth by allowing water and nutrient filtration into the soil adjacent to the plant. 
In some cases soil bacteria will be attracted to root compounds, but exude antibiotics that repel other types of soil life-- making a niche for itself to flourish. This is one reason for crop rotation. Once a particular specialized microscopic community has developed, the microenvironment may become unfavorable to certain types of plants. Planting different plants with different exudate signatures will prevent the accumulation of unfavorable soil bacteria and maintain an overall balance within the soil.
The plowzone which comprises the upper 20 to 30 cm of soil on cultivated sites is the disintegrated, homogenized rhizosphere.
Soil Animals. Soil animals include earthworms, microarthropods, nematodes, and insects. Soil animals are classified into microfauna (mainly protozoa); mesofauna (mites, collembola [springtails] and nematodes); and macrofauna (earthworms, beetles and termites). All of these are concentrated in the upper 5 cm of soil. Megafauna are biological animals that burrow and dig into the soil and to varying extents modify its integrity. Megafauna include burrowing animals such as gophers, mice, voles, and rabbits.  Of the digging animals, man has been the most devastating to the integrity of soil.
Charles Darwin was one of the first to study the role of earthworms as soil building animals . But, not all earthworms are adapted to all soils. Learn about the ecological devastation caused by exotic earthworms in this thread in the soil and composting forum, where greenbrain, equilibrium, and snapple present links to all you need to know about the threat of exotic earthworms.
Soil Chemistry. The chemical properties of soil affect fertility and include processes such as nitrogen fixation, sulfur oxidation, and organic decomposition. Cation Exchange Capacity (CEC) is the capacity of the soil to hold cations, or positively charged ions. Positively charged ions may be hydrogen, calcium, potassium, ammonium, or sodium ions, for example. Positively charged cations bind to negatively charged soil particles. CEC, expressed as CEC = meq/100g of soil, varies with different soil textures. Sand, for example has a very low CEC: only 2 - 4 meq/100 g of soil. While loam has 7 - 6 meq/100 g of soil, but clay has 40 - 60 meq/100 g soil. Organic matter has the highest of all. It has a CEC of 50 to 300 meq/100 g. soil. So you can see the importance of adding organic matter to soil. Organic matter improves soil fertility far beyond the CEC of soil that has no organic matter in it, even if commercial fertilizers are added to the soil. 
Physical Properties of Soil; Structure and Texture. The physical properties of soil are those characteristics that affect water movement and root penetration: structure and texture. Soil structure is the aggregation of particles and pores between them, while texture is the relative proportion of clay and sand. Because clay soils have the finest texture and pore size, they hold the greatest amount of water. They also hold heat better so they allow earlier planting in the spring and they can be gardened later in the fall. Clay soils also hold more ionized minerals or nutrients. But, they are easily compacted and harder to till. So, with correction for drainage by adding organic matter, clay soils are excellent candidates for gardens. The ideal garden soil texture is usually considered to be loam, which contains a percentage of clay: 40% sand, 40% silt, and 20% clay. In this thread in the Soil and Composting Forum, eden 100 discusses how to manage clay soil.
Cultivation not only disturbs natural biological processes within soil, but it also destroys scientific information necessary to the understanding of what those natural biological processes are. At least two kinds of scientific disciplines are dependent upon undisturbed soil: pedologists, or soil scientists and archaeologists who interpret past human behavior from the information in soil.
Fig. 4 is a typical soil profile. A soil profile is an arrangement of layers or soil horizons. The letters O, A, B, C, E, and R are used to describe the master horizons within a soil profile. The O or organic horizon consists of leaf litter and/or humus. The A horizon is the topsoil consisting of humus and minerals. The subsoil horizon, designated B, consists of clay and mineral deposits from the upper horizons such as iron, aluminum oxide, and calcium carbonate. Horizon C is also called the regolith, it occurs above the R horizon and below the B horizon. It consists of slightly broken up bedrock. It contains very little organic matter. The E horizon is an eleuvian or leached layer consisting of demineralized sand and silt. It is beneath the A horizon and above the B horizon. The R horizon is bedrock.  
Many people think archaeology is about recovering artifacts, but in fact it is about reading soil profiles, depositional sequences, or stratigraphy. Figure 5 shows the stratigraphic trenches left after the excavation of a complex burial mound. Figure 6 is a profile from the same burial mound Site 1Ms300 on the Tennessee River excavated by The Tennessee Valley Authority (TVA ) in 1975.
On archaeological sites that have been subjected to cultivation the upper 20 to 30 cm is called the plowzone. It is routinely scraped away with a front end loader before actual excavation can begin, because any information it may have contained was destroyed by cultivation.
Fig. 5. Stratigraphic Trenches after Excavation Fig. 6. Stratigraphy within the Burial Mound.
Based upon global land use data, Admundson compares the percentage of the earth's surface area devoted to grasslands, woodlands, forests, and deserts, and tundras after the development of culturvation. The earth's cultivated surface area has increased +1760.0% compared to the preagricultural era. Cultivated land has had a differential impact upon other pre-agricultural land-use types. Grasslands have decreased in favor of cultivation by -19.4%, woodlands by -18.6% and forests by -16.0%. The effect of cultivation on deserts and tundras has been negligible.  This of course reflects the global success of agricultural civilization, but at the expense of significant losses to major earth eco-zones. The loss of grasslands and forests affects the biological species dependent upon those habitats. And we are learning now that the loss of forests has severely affected global climate. The shift of land use to cultivation has therefore not only affected the habitats of other species, but it has profoundly modified the habitat of man himself.
Fig. 7. Snowshoe Hare Lepus americanus. Inhabitant of the Tundra,
A Zone Not Significantly Impacted by Cultivation.
 Fukuoka, M. One Straw Revolution: The Natural Way of Farming. Emmaus, Pennsylvania, Rodale Press, 1978.
-------- the natural Way of Farming: The Theory and Practice of Green Philosophy. Tokyo and New York: Japan Publications. 1985.
 Lee Reich. Weedless gardening. Workman Publishing. New York. ISBN 0-7611-1696-6
 Shapiro, Howard-Yana and John Harrisson. Gardening for the Future of the Earth. Bantom. Jan 4, 2000. ISBN-10: 0553375336, ISBN-13:978-0553375336
 a. Soil Solarization. ucce.ucdavis.edu pdf b. University of California. Soil Solarization - Informational Website. Dr. James Stapleton, IPM. Plant Pathologist. Kearney Agricultural Center, Parlier, California. solar.uckac.edu
Figure 5. Cole, Gloria G. The Murphy Hill Site, 1Ms300: The Structural Study of a Copena Mound and Comparative Review of the Copena Mortuary Complex. Research Series No. 3. The Office of Archaeological Research. The University of Alabama. Tennessee Valley Authority Publications in Anthropology. No. 31. 1981. Stratigrahic Trenches after Excavation. Site 1Ms300, Marshall County, Alabama. TVA Excavation, 1975.
Figure 6. Cole, Gloria G. Ibid. 1981. Stratigraphy within the Burial Mound 1Ms300, Marshall County, Alabama. TVA Excavation, 1975.
Figure 7. Snowshoe Hare. Lepus americanus. Inhabits the forests and tundra regions of the northern U.S. and Canada. Its habitat is not threatened by cultivation. Photograph source: Private Collection.
DEDICATION: To Carol Eads, who has taught all of us who cared to listen the spirit of survival--of living strong in a harsh improbable environment, and of preserving her traditional culture as a Native Alaskan in modern times.
About Gloria Cole
I am a retired archeologist and curator of an historic house museum. I live in Greensboro, Alabama, a small rural historic Southern town, with my two dogs, a rabbit and (by recent count) two cats. I am upgrading a 100 year old neoclassic house and clearing and planting my two-and-one-half acre property. Of plants, I love roses best of all.