I'll start off by saying that I am neither an economist nor a statistician. I'm also not sure what you mean by "plantations," so I'm just going to talk about agricultural output and land revenue.

During the time period you're interested in, India was a net exporter of agricultural and raw materials, and an importer of manufactured goods. Most of the exports were rice, wheat, and cotton, alongside things like oil seeds, jute, hides, and tea. These all generated a large amount of money for India itself, and especially for the governing British system.

To give us an idea of how much they generated, first we have some of the writings and reports of Dadabhai Naoroji, an Indian politician and influential figure around this time. He put together analyses of the economic situation of India under British rule and its consequences, and helped found the Indian National Congress, an organization instrumental in the Independence Movement.

In an 1876 essay/speech entitled Poverty of India, he estimates the total agricultural output of India, discounting products like straw and seed for the following year, to be at most £260,000,000 "as the produce of cultivation, during a good season, for human use and consumption in a year." His statistics come from yearly agricultural reports (of varying completeness and quality) made to a statistical committee in Calcutta as requirement by the British Parliament, and other official reports, mostly dealing with the seasons from 1867-1870.

Naoroji and the Under-Secretary of State for India at the time, estimated the annual income of India to be roughly around £300,000,000 in 1871, a figure endorsed by the Viceroy of India, Richard Bourke. Out of this, £65,000,000 was money raised for the government. This is in accordance with a later figure given by the economic historian Romesh C. Dutt in his 1902 book The Economic History of India in the Victorian Age, (pdf link) where he estimates the annual average revenue of India between 1891 and 1901 to be £65,000,000. The estimate is the same despite the fact that there's a 20 year gap between Naoroji's estimate and Dutt's estimate, (but it may be somewhat remiss of me to compare them due to changes in currency value, like the lessening value of the rupee over time.) So if you look at the agricultural production of £260,000,000 and consider the £65,000,000 needed for the government, about a quarter of British India's agricultural output could go towards governance.

As part of the British Empire, India incurred fees known as "Home Charges," which were funds taken as interest on railway building and on British India's debt. Part of this debt rolled over from the days of East India Company rule, more was accrued to pay for the 1857 Rebellion, and additional funds were needed to help pay for military conflicts outside of India (China, Sudan, the Afghan Wars, ect...) These charges also included things like retired officers' pensions and fees levied for the civil and military administration of India. Dutt tells us that in 1901, the Home Charges totaled £17,000,000, while the amount of land revenue (i.e. money raised for renting agricultural land and the like) totaled £17,500,000. So the money made off the renting of land itself, not just crop export, could roughly pay for the Home Charges that year.

If this didn't answer your "plantations" question, I hope it at least gave you an idea of the importance of agriculture to the British Indian economy.