Assertion: In India irrigation facilities are also required even in the areas of ample rainfall like West Bengal and Bihar.
Reasoning: In the absence of irrigation facilities, breaks in monsoon or its failure creates dry spells which will be detrimental for agriculture.

Both Assertion (A) and reasoning (R) are correct and R is the correct explanation of A.

In agriculture, water is mainly used for irrigation. Irrigation is needed because of Spatio-temporal variability in rainfall in the country. The large tracts of the country are deficient in rainfall and are drought-prone. North-western India and Deccan plateau constitute such areas. Winter and summer seasons are more or less dry in most part of the country. Hence, practicing agriculture without assured irrigation during dry seasons is difficult. Even in the areas of ample rainfall like West Bengal and Bihar, breaks in monsoon or its failure creates dry spells detrimental for agriculture. The water need of certain crops also makes irrigation necessary. For instance, rice, sugarcane, jute, etc. water requirement is very high and can be met only through irrigation.