Potassium resource quantity of main grain crop straw and potential for straw incorporation to substitute potassium fertilizer in China

Objectives Crop straws contain high content of potassium (K), and the in-season K release rates of returned straws are high in Chinese croplands. Clearance of the quantity of crop straws and the contained K resources in the main grain crops planting areas of China would provide a scientific basis for soil K management under straw returning.

Methods Based on latest statistical data and literature review, the K resource quantity of main grain crop straws and the potential of K fertilizer substitution were estimated for different provinces and agricultural regions of China.

Results The results indicated that the amounts of crop straw from rice, wheat and maize were 232.12, 170.83 and 399.18 million tons per year, in the main grain crops-planting regions of China during 2015–2017. The crop straws were mainly produced in North China, Middle and Lower Reaches of Yangtze River, and Northeast China, accounting for 33.6%, 25.4% and 22.8% of the total national crop straw yields, respectively. The annual straw K resources from rice, wheat and maize were 5.29, 2.16 and 5.68 million tons. The straw K resources were mainly distributed in Middle and Lower Reaches of Yangtze River, North China and Northeast China, accounting for 30.4%, 28.2% and 22.0% of the whole resources in China. The K₂O provided by rice straw incorporation ranged from 115.0 to 209.5 kg/hm² in China, that by wheat straw incorporation was relatively higher (K₂O 82.3–97.1 kg/hm²) in Henan, Hebei, Shandong, Anhui and Jiangsu Provinces, where the sowing areas of wheat was about 71.1% of China. For maize, straw incorporation could substitute 67.2–170.7 kg/hm² of K₂O input. At the national scale, the substituting potentials of potash through straw incorporation were K₂O 152.6, 82.4 and 124.4 kg/hm² for rice, wheat and maize, respectively.

Conclusions The straws of rice, wheat and maize could averagely provide K₂O resources of 4.49, 1.93 and 4.79 million tons annually under straw returning. The available K₂O amount in season from rice, wheat and maize straws are 152.6, 82.4 and 124.4 kg/hm² in China. Therefore, using straws properly could satisfy the basic potassium requirement for grain production and soil potassium balance.