floods and expands its banks in September or early October. Before the flooding occurs, the seed is spread on the ground without any preparation of the soil, and the floating rice is harvested nine months later, when the stems have grown to three or four meters in response to the peak of the flood (the floating rice has the property of adjusting its rate of growth to the rise of the floodwaters so that its grain heads remain above water). It has a low yield, probably less than half that of most other rice types, but it can be grown inexpensively on land for which there is no other use. The per-hectare rice yield in Cambodia is among the lowest in Asia. The average yield for the wet crop is about 0.95 ton of unmilled rice per hectare. The dry-season crop yield is traditionally higher—1.8 tons of unmilled rice per hectare. New rice varieties (IR36 and IR42) have much higher yields—between five and six tons of unmilled rice per hectare under good conditions. Unlike local strains, however, these varieties require a fair amount of urea and phosphate fertilizer (25,000 tons for 5,000 tons of seed), which the government could not afford to import in the late 1980s. Effect of changing climate Unseasonable droughts and unpredictable rainfall are increasingly disrupting rice cultivation and forcing Cambodian farmers to search for jobs in cities. Traditional rice farming relied on rain falling predictably two times a year, which used to occur with regularity. rains tend to fall in one short downfall. Other crops The main secondary crops in the late 1980s were maize, cassava, sweet potatoes, groundnuts, soybeans, sesame seeds, dry beans, and rubber. According to Phnom Penh, the country produced 92,000 tons of corn (maize), as well as 100,000 tons of cassava, about 34,000 tons of sweet potatoes, and 37,000 tons of dry beans in 1986. In 1987 local officials urged residents of the different agricultural regions of the country to step up the cultivation of subsidiary food crops, particularly of starchy crops, to make up for the rice deficit caused by a severe drought. The principal commercial crop is rubber. In the 1980s it was an important primary commodity, second only to rice, and one of the country's few sources of foreign exchange. Rubber plantations were damaged extensively during the war (as much as 20,000 hectares was destroyed), and recovery was very