Dear student
(a)Irrigation is done to add moisture to the soil and to provide water to plants in the right amount for their proper growth and development. If irrigation step is not done the plants will not get water for their growth and after some time they will die due to lack of water.
(b)Natural source of irrigation: River and Lake
(c)Since the rate of transpiration increases during summer and thus to fulfill the requirement of water, the frequency of irrigation increases in summer.
Regards