Spatial-temporal changes in grain input-output and the driving mechanism in China since 1985

Based on Chinese county-level statistic data, this paper reveals spatial-temporal distribution and changing of grain production, by studying gravity centres of grain input-output regions in China from 1985 to 2009. According to the grain output, per-capita grain consumption, and population, the surplus grain of 2864 counties from 1985 to 2009 was calculated. And the counties with surplus grain value greater than zero and smaller than zero were respectively defined as grain input regions and grain output regions; they were respectively analysed by using the model of grain gravity centre. We found that there are four periods of spatial-temporal changing of gravity centres in grain input regions, and five periods in all output regions. According to the moving path of the gravity centres of input-output regions, 1990 was the turning point of completely entering into 'grain supply from north to south period'. Spatial-temporal changing of grain-sown area and the arable land was the main driving mechanism for the shift in grain input-output gravity centres. The change of spatial pattern of grain production influenced sustainability of grain production from three impacts. And two policy suggestions are put forward to promote the sustainability of grain production.