Was there an increment of the percent of people working in the agricultural sector during the economical crises of the last couple of centuries?
What are the factors influencing the ratio of farmers?
The chief impact on the ratio of agricultural workers to workers in all other industries has been the dramatic growth of workers in other sectors.
Agricultural workers have increased in number at times, particularly with the proletarianisation of peasants, petits-bourgeois, and lumpen-proletarians in the development of modernity. The "total workforce" has also changed. Small scale industry has reduced, but large scale mobile regional workforces have increased. Labour has flowed from capital intensive sectors towards labour intensive sectors. Workers are generally where the profit isn't.
Moreover, the "farmer" the owner operator of a family concern, even if they exploited itinerant workers, has been reduced in power and status to a locked-in-contractor.
Noel Butlin's data on Australian agriculture is good here, as is the account in Connell and Irving, Class structure in Australian history.