The regional test yields of certificated cultivars of grain crops represent the potential yields for the given region under the current natural and technical conditions. Therefore, it is appropriate to use the regional test yields to estimate the gross grain potential of Mainland China. In this paper, we calculated the grain potential of cultivated lands for each of the 105 agro-ecological regions in China. First, cropping system in each agro-ecological region was assumed to be the best use of the agro-climatic resources. Second, the potential per hectare for each of the crops was calculated for a given agro-ecological region, based on the regional test yields of certificated cultivars of grain crops in a given cropping system. For rain-fed and dry lands, their grain potentials were further modified by water-restricting coefficients. The water-restricting coefficients were calculated by dividing the hydro-thermal potential with the corresponding photosynthesis-thermal potential for different grain crops, which were obtained from Regulations of Farmland Grading. Thereafter, the grain potential per hectare of each agro-ecological region was calculated considering the cropping system and the potentials per hectare of all the crops in the cropping system. The gross grain potential of each county in a given region was then obtained by multiplying the grain potential per hectare and the total area of cultivated lands in the county. Finally, the gross grain potential of each agro-ecological region and the whole Mainland China were obtained by summarizing the grain potentials for all of the counties. The results showed that the gross grain potential of Mainland China was 0.92 billiont in 2004. It should be pointed out that this calculation on the grain potential did not sufficiently consider the crop growth restricting factors of cultivated lands, such as soil fertility, fertilizer input, and so on. Since the grain potential is far above the actual grain yield, it suggests that the cultivated land assurance for grain security in Mainland China is relatively high. The results of each agro-ecological region showed that the highest grain potentials were distributed in Huang-Huai-Hai Plain, Northeast China, Middle and Lower Reaches of Yangtze River and Sichuan Basin, where excellent hydro-thermal condition and flat terrain are ideally suitable for crop growth. (C) 2008 Elsevier Ltd. All rights reserved.
