Crop rotation:
improves soil fertility
shortens the growing season
has only been in use for a few years
is only worthwhile for small farmers

mountains can affect the climate of nearby lands. in some areas, mountains block rain, so that one side of a mountain range may be rainy and the other side may be a desert. much of airborne moisture falls as rain on the windward side of mountains.

explanation:

when atoms of different types of elements join together, they make molecules called compounds. water consists of compound molecules made up of 2 hydrogen atoms and 1 oxygen atom. this is why it's called h2o. water will always have 2 times the number of hydrogen atoms as oxygen atoms.