Abstract: In the past decade, farmland expanded remarkably in many regions in the arid Northwest China. These changes occurred in the context of rapid loss of farmland and exacerbated degradation of local environments in China. Therefore, better understanding their causes is helpful for understanding land use changes in China and crucial for developing effective conservation and ecosystem management plans. In literature, it is suggested that local population growth, technological progress in agriculture, and policy prompting are the main causes. However, these suggestions root in statistical correlation without further empirical research. In this paper, we took Xinjiang region as the sample, and evaluated the rationality of these suggestions based on changes in sown area. The results imply that technological progress in agriculture and policy prompting assuredly accelerate the expansion of farmland, as the sown areas of leading crops increase at higher rates in response to the adoption of technologies and policies. Meanwhile, the increasing need of food due to population growth does not consequentially cause the expansion of farmland, as the sown area of food plants decreases in the same period. From the results of sown area changes, the pursuing for scale benefit of crops with higher returns can be inferred as the main cause of farmland expansion.

Key words: farmland expansion, Northwest China, policy prompting, population growth, technological progress, Xinjiang