to 1982 it was estimated that Malawi had sufficient arable land to meet the basic food needs of its population, if it were distributed equally. By 1992, cultivation had spread to hillsides and onto steep Rift Valley slopes where it was unsustainable. The area of smallholder maize increased 20% between 1968 and 2000 by using marginal land. Many rural smallholdings were less than two hectares in the 1960s: by the mid-1980s the average plot was hardly more than one hectare. Throughout most of the 20th century Malawi's main food crop was maize and at the end of that century, 90% of its grain was maize, which provided 56% of all calories consumed. Malawi was the world's most maize-dependent country, except for Zambia. Its traditional substitutes were cassava on the Lakeshore and sweet potatoes in the Shire floodplain. The estimated area of maize cultivation increased from around 1.3 million hectares in 1980 to over 1.6 million hectares in 2000. However, maize harvests began to fluctuate widely, from highs of about 1.5 million tonnes in 1989 and about 1.3.million tonnes in 1990 to lows of about 0.6 million tonnes and about 1994 and 0.8 million tonnes in 1992. In view of the fluctuation in maize harvests, from the 1990s crops of sweet potatoes and cassava increased the result of USAID projects to promote drought-resistant foods. The area of cassava planted is estimated to have increased from 72,000 hectares in 1990 to over 200,000 hectares in 2001, with estimated output increasing from 168,000 tonnes in 1990 to 3.4 million tonnes in 2001. The area of sweet potatoes planted is estimated to have increased from 43,000 hectares to over 192,000 hectares between 1990 and 2001, while estimated output increased from 177,000 tonnes to 3.4 million tonnes over the same period. There is some disagreement about the magnitude of this increase, but they suggest that maize is no longer the most important crop by tonnage, although it still accounts for 60% of the area of food planted. Despite a collapse in tobacco prices in 1979, The World Bank thought growing Burley tobacco by smallholders would relieve poverty by allowing farmers to buy imported cheap maize for food. From 1987, market liberalisation allowed smallholder to grow Burley, and they could only sell it freely in 1996173. The richest 25% of smallholders earned significant amounts from Burley after liberalisation. Malawi's Burley production increased from 45,600 tonnes, all