How does the transfer of crops encourage changes in farming and irrigation techniques?

The question does not say which transfer so I guess it is the transfer of crop from South Asia to Middle East. This brought major changes due to some common factor involved. Different crops need different climate to grow better and this transfer provided that, especially to rice and cotton. Irrigation techniques were improved for example a technique used by Persians in about 1000 BC was called "Qanat", which brought water through tunnels to surface from the basins which caused a reduced amount of labor and a better irrigation system. 

as resources become scarce because of population growth, the growth decreases after few years due to lack of resources and food.