SOURCE: Natural tilth is created when the biodiversity of life in the soil causes the soil particles to aggregate or bind together in small clumps. The areas separating these clumps are Macro and Micro pores they are used to store air and water within the soil. Without these pores there would be no space between soil particles for air, water or plant roots. The soil would then provide a poor environment for plant growth. New humus binds to clay particles, glues secreted from various life in the soil cause the soil to form larger aggregates, which are tied together by fungal hyphae and root hairs .
EFFECT: Natural tilth is self-sustaining so long as an environment is maintained where plant residues and these fragile glues are not mineralized by decomposition into base compounds and elements. If this system is circumvented natural tilth is lost. But will return in time once the biodiversity of life in the soil heals itself. The symbiosis of the diverse life in the soil work together. Earthworms for example increase under this system. Their channels allow air and water to travel deep into the soil. Undisturbed decaying plant roots also leave channels deep into the soil. Keeping the root environment aerobic is one of the most important fundamentals of soil and plant health, as most pathogens are anaerobic. Secretions from the roots create a positive environment for organisms that help feed plants. Symbiotic relationships with Arbuscular Mycorrhizal fungi make nutrients tied up in the soil like P, Cu and Zn available.
SOURCE: Tillage is passing some type of implement through the soil to force it apart and blend air into the soil to create the needed pore space for plant growth. While man rather than nature now provides the tilth, this act also stops the natural system from providing tilth. This happens when the breakdown of plant material no longer takes place near the surface by organisms that leave the residue as humus a stabile sequestering of the compounds but breaks them into base components called mineralization.
EFFECT: Manmade tilth is not self-sustaining in fact hard layers often form just below where the tillage stops and forms a barrier to plant roots, deeper tillage is then often recommended to fracture this layer. Manmade tilth requires significant energy to provide the power to fracture the soil. Also a significant investment in tools needs to be maintained. Manmade tillage results in less residue cover to intercept raindrops, lower organic matter levels to store water in the soil, a lower ability to hold nutrient cat ions, more energy required in the production process and a much higher susceptibility to erosion.