China crop swtich (IMAGE) PNAS Nexus Caption Spatial variations in county-based crop fraction changes, defined as the fraction of crop-sown area over total cropland area. Credit Guan et al. Usage Restrictions None License Original content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.