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In terms of the improved Kassam-Wageningen method,calculation is made of the effects of light,temperature,climate and soil on sweet potato productivity at 29 stations over Fujian Province.The results show that under the optimal water and fertilizer condition,the climate productivity and climate-soil productivity will increase by one third or more.According to the characteristics of food production in Fujian Province,some useful countermeasures for food security are put forward: increase the planting area of sweet potatoes;build the yield-stable croplands despite drought or excessive rain;improve soil fertility;limit the non-agricultural lands and the growth of population.