Patterns and causes of winter wheat and summer maize rotation area change over the North China Plain

Liu, Zhengjia   Liu, Yansui   Dong, Jinwei   Baig, Muhammad Hasan Ali   Chi, Wenfeng Peng, Liuying   Wang, Jieyong

Cropland area and cropping frequency play very crucial roles in determining regional food production. However, rapid urbanization accompanied by declining surplus-agricultural labor force has greatly altered patterns of agriculture land use and cropping frequency. Due to lack of continuous cropland and cropland-use intensity maps, our knowledge is still limited to understand whether the urbanization process must have a negative effect for changes in cropland-use intensity. Herein, we took the North China Plain (NCP), both the largest winter wheat and summer maize rotation area and rapidly urbanized area in China, as the study area, and used 250 m moderate resolution imaging spectroradiometer NDVI anomaly data, the correlation of NDVI time series in two neighboring years and machine learning algorithms to investigate spatiotemporal patterns and trends of cropland area and cropping frequency change over the NCP from 2000 to 2019. Results showed a significantly decreased cropland area observed since 2004 (slope = 783.8 km(2) a(-1), p < 0.01), while area of double-season cropping presented a relatively steady trend (slope = 446.9 km(2) a(-1), p = 0.335). As expected, decreased croplands were mainly occupied by urban and built-up land expansion, however, existing cropland-use intensity was yet improved. Patterns and trends of double-season cropping types were varied spatially. Particularly, the area of winter wheat and summer maize rotation presented a significantly increasing trend (slope = 3423.3 km(2) a(-1), p < 0.01). Furthermore, the respective area of winter wheat and summer maize both displayed significantly increasing trends with slope of 2953.8 and 2874.9 km(2) a (-1)(p < 0.01) in entire period. Land-use and grain subsidy policies are considered as largely responsible for this phenomenon. These satellite-observed findings highlight that positive land-use policies and managements will be helpful for profitably keeping/improving the harvest area.

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