Irrigation is human being's efforts to substitute for any deficiency in natural rainfall with the objective of a steady expansion in crop output. The impact of irrigation on income/output is a difference between the magnitude of irrigated and un-irrigated income/over all crop yield per hectare.
Links:
[1] http://admin.indiaenvironmentportal.org.in/feature-article/impact-irrigation-cropping-pattern-input-utilization-productivity-and-net-returns
[2] http://admin.indiaenvironmentportal.org.in/category/author/pratap-singh
[3] http://admin.indiaenvironmentportal.org.in/category/author/s-p-saraswat
[4] http://admin.indiaenvironmentportal.org.in/category/author/ranveer-singh
[5] http://admin.indiaenvironmentportal.org.in/category/journal/agricultural-situation-india
[6] http://admin.indiaenvironmentportal.org.in/category/thesaurus/agriculture
[7] http://admin.indiaenvironmentportal.org.in/category/thesaurus/irrigation
[8] http://admin.indiaenvironmentportal.org.in/category/thesaurus/himachal-pradesh