Zero Emission

An engine, motor or other energy source that does not produce any gas or release any harmful gases directly into the environment.

Zero emissions

zero population growth (ZPG) The number of births at which people are just replacing themselves; also called the replacement level of fertility.


Zero tillage

Zero tillage (No-tillage) is a minimum tillage practice in which the crop is sown directly into soil not tilled since the harvest of the previous crop. Weed control is achieved by the use of herbicides and stubble is retained for erosion control. It is typically practiced in arable areas where fallowing is important.

zone of aeration Upper soil layers that hold both air and water.


zone of leaching

The layer of soil just beneath the topsoil where water percolates, removing soluble nutrients that accumulate in the subsoil.

zone of saturationLower soil layers where all spaces are filled with water.