This paper presents an investigation of the relations in China between farm output, the natural fertility of agricultural land, and the use of anthropogenic farm inputs. The methodology is presented as a potential increment to the analysis of the effects of climate change in agriculture. Variations of climate, soil and topographic conditions, and direct farm inputs across the prefectures of China are used to determine their effects on the output of particular crops. The study estimates crop production functions with conventional land, labor, fertilizer and mechanical inputs, and the net primary productivity (NPP) projections of the Terrestrial Ecosystems Model to reflect climatic conditions. Estimates of the NPP of the land in each prefecture are used to simulate the effects of climate and other natural growing conditions. The results suggest that there is substantial scope for increasing food production in China by increasing its irrigation of farm land and the use of farm inputs of fertilizer and mechanical power.