How does the new index of rents influence our understanding of the fortunes of agriculture in the period 1690–1914? In this chapter and the one which follows we attempt to assess the index against the broader history of agriculture, and in particular we look in some detail at the pattern of prosperity and depression. We shall attempt to link changes in agricultural practice, and in output and productivity, to the rent index, in order to establish the relationship between rent levels and broader changes in agricultural practice. We are well aware that the correlation is not straightforward. Rents did not rise or fall merely in step with alterations in output: the pattern of change was much more complex than this, but rental data is particularly useful for identifying booms and slumps and our concern will be to look for links with agricultural change more generally.

Why did rent levels change over time? We may identify several main causes. The first is competition for land. Clearly rack-rented land will be subject to rental fluctuations according to demand for farms generally, and for particular types of farm (either in terms of size, or soil, or culture, or proximity to markets, etc.). Agricultural experts opposed the letting of farms simply to the highest bidder but had few ideas as to how to establish what a reasonable rent should be (chapter 2). Yet as the eighteenth century passed into the nineteenth, and as tenancies for leases and lives were converted to tenancies on medium-term leases, or became tenancies at will, rack-rented farms could indeed have become subject to market forces, with rents varying appropriately.