Abstract
Mapping rice cropping systems is important for grain yield prediction and food security assessments. Both single- and double-season rice are the dominant rice systems in central China. However, because of increasing labor shortages and high costs, there has been a gradual decline in double-season rice. Ratoon rice (RR) has been proposed as an alternative system that balances the productivity, cost, and labor requirements of rice cultivation. RR has been expanding in central China, encouraged by the improved cultivars, machinery, and favorable policies. However, to our knowledge, the distribution of RR has not been mapped with remote sensing techniques. This study developed a phenology-based algorithm to map RR at a 10 m resolution in Hubei Province, Central China, using dense time stacks of Sentinel-2 images (cloud cover <80%) in 2018. The key in differentiating RR from the other rice cropping systems is through the timing of maturity. We proposed to use two contrast vegetation indices to identify RR fields. The newly-developed yellowness index (YI) calculated with the reflectance of blue, green, and red bands was used to detect the ripening phase, and the enhanced vegetation index (EVI) was used to detect the green-up of the second-season crop to eliminate the misclassification caused by stubbles left in the field. The RR map demonstrated that RR was mainly distributed in the low alluvial plains of central and southern Hubei Province. The total planting area of RR in 2018 was 2225.4 km2, accounting for 10.03% of the total area of paddy rice fields. The overall accuracy of RR, non-RR rice fields, and non-rice land cover types was 0.76. The adjusted overall accuracy for RR and non-RR was 0.91, indicating that the proposed YI and the phenology-based algorithm could accurately identify RR fields from the paddy rice fields.
Highlights
Rice (Oryza sativa) cropping systems are of great importance for global food security [1]
Comparing the time series of the enhanced vegetation index (EVI) and the land surface water index (LSWI) of ponds that grow aquatic plants and the paddy rice fields, we found that the EVI over the ponds increased sharply in June and reached higher EVI values than over paddy rice fields
The key in differentiating Ratoon rice (RR) from other rice cropping systems is its different timing of maturity
Summary
Rice (Oryza sativa) cropping systems are of great importance for global food security [1]. China is the largest rice-producing country, accounting for 28% of global rice production [2]. Middle- and double-season rice are the dominant rice systems in central China [3]. Intensive cropping systems result in adverse impacts on the environment [4] as well as in higher production costs. Double-season rice systems in central China have progressively shifted into single-season rice mainly due to high costs and an increase in labor shortages [5]. There is a growing interest in identifying an alternative rice system that can increase the productivity while reducing the environmental impact and the labor cost of existing cultivation practices
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