There is a direct correspondence between agricultural productivity and the agrarian structure. In areas of assured irrigation, those with plenty rainfall or artificial irrigation works (such as rice-growing regions in river deltas, for instance the Kaveri basin in Tamil Nadu) more labour was needed for intensive cultivation. Here the most unequal agrarian structures developed. The agrarian structure of these regions was characterized by a large proportion of landless labour, who were often 'bonded' workers belonging Rose to the lowest castes.