"In some cases, the difference is enormous. A recent study of farming in Turkey, for example, found that farms of less than one hectare are 20 times as productive as farms of more than 10 hectares. Sen's observation has been tested in India, Pakistan, Nepal, Malaysia, Thailand, Java, the Philippines, Brazil, Colombia and Paraguay. It appears to hold almost everywhere.
The finding would be surprising in any industry, as we have come to associate efficiency with scale. In farming it seems particularly odd, because small producers are less likely to own machinery, less likely to have capital or access to credit, and less likely to know about the latest techniques." (Thanks Leila)
Monbiot on how small farmers are the way to go. Essential reading.