by Paul Polak There are at least 50 million poor farmers who use sprinkling cans to irrigate quarter acre vegetable plots and sell what they grow to customers in cities and towns in Asia and Africa. I  have interviewed hundreds of them, and have no doubt that they can double or triple their incomes with access to improved affordable irrigation, farming methods, and access to markets. Here is a case in point. In August, 2009, Bob Nanes, (IDE Ghana), Sue Haley (IDE Africa) and I visited 14 sprinkling can farmers who produce vegetables for the million or so people who live in Kumasi, Ghana. Here’s…