Changes of cropping structure lead diversity decline in China during 1985-2015.

China's agriculture is in the transformation and development stage to adapt to the influences of climate change, technological progress and the requirements for resources and environmental protection. Optimization of cropping structure variation in the new stage is urgent. Our study systematically described the spatiotemporal variation in crop patterns in China from 1985 to 2015 and further analyzed the changes in cropping diversity and dominant cropping structure based on a county-level agricultural database. The results showed that the planted areas of staple crops and oil crops had expanded in three major grain-producing areas. Coarse crop planting has been gradually replaced by staple and oil crops. A slight increasing trend occurred in tuber crop planting in southwestern China, and fiber crop planting had already transferred from eastern to northwestern China. Moreover, cropping diversity has decreased in northern China, especially in the Northeast China Plain and North China Plain, while a slight increase has occurred in the south. Cropping structure has been simplified in past decades and it basically formed a single cropping structure dominated by staple or oil crops. Further cropping structure adjustments should focus on resource-saving, ecofriendly, intensive and efficient industrial coordination goals, adapting to the mechanization, scale and precision developments of agricultural production. It is important to develop a multifunctional innovative farming system and technology to ensure national food security.