About 78% of Iceland is agriculturally unproductive, and only about 1% of the land area is actually used for cultivation. Of this amount, 99% is used to cultivate hay and other fodder crops, with the remaining 1% used for potato and fodder root production. There were about 4,000 full-time farmers in the 1990s, with about 75% living on their own land; some holdings have been in the same family for centuries. In the 19th century and earlier, agriculture was the chief occupation, but by 1930, fewer than 36% of the people devoted their energies to farming, and the proportion has continued to fall. Hay is the principal crop; other crops are potatoes, turnips, oats, and garden vegetables. In hot-spring areas, vegetables, flowers and even tropical fruits are cultivated for domestic consumption in greenhouses heated with hot water from the springs. Besides hay and other fodder crops, about 9,000 tons of potatoes were produced in 1999. There are agricultural institutions in Borgarfjörur, Hjaltadalur, Hvanneyri, and Reykir; between 15–20% of all farmers have finished an agricultural degree program.