Zero is an agricultural practice. It maintains permanent Soil cover. It increases natural biological processes that occur in the soil. It improves sustained crop production and increases soil Nutrition. There is no soil disturbance.
Tillage is land preparation. Tilling of land means agitating the soil particles by overturning, digging and stirring. This is done to kill Weeds, crop residues and to aerate the soil. However, tilling destroys natural structure of the soil. If greater soil area is exposed to sunlight (which usually happens while tilling with the help of tractors), the moisture retaining capacity of soil is lost. On the other hand, zero tillage skips the tilling process. Here the crop seed is sown without land preparation. And the seeds are drilled into the soil.