Children walk through a field where watermelons grow on sand fields in Xingren township in Zhongwei City of Ningxia Hui Autonomous Region July 23, 2008. Agricultural techniques invented by local farmers prevent water loss and soil erosion in the sand fields. Planting Watermelons has become an industry in Zhongwei. These watermelons sell well in more than 20 provinces and cities of the country such as Beijing, Shanghai and Guangzhou. [Xinhua]