Distribution of rice straw phosphorus resources in China and its utilization potential under straw return

Large amounts of rice straws are produced in the main rice-cultivating areas of China. Rice straw returning is a major contributor of phosphorus input in the field. Clarification of the contribution of rice straw returning to soil phosphorus input could provide scientific references and guidance for the optimization of phosphorus management and the regulation of soil phosphorus balance. Based on the rice production statistics from China Rural Statistical Yearbook and related data from a literature survey, the temporal and spatial distribution characteristics of rice straw phosphorus resources from 2013 to 2018 and the amount of straw phosphorus returning to soil per unit sown area were estimated for different rice-cultivating provinces and regions of China. In 2018, the amounts of straw from early rice, double cropping late rice, and medium and late rice in the main rice-cultivating areas of China were 23.27, 27.83, and 135.27 million tons, respectively. Rice straw was mainly produced in the Middle Reaches and the Lower Reaches of Yangtze River, accounting for 33.6% and 21.8% of the total national rice straw yields, respectively. The rice straw phosphorus resources was tended to increase from 2013 to 2018, increasing from 0.597 million tons phosphorus pentoxide (P₂O₅) in 2013 to 0.628 million tons P₂O₅ in 2018. The rice straw phosphorus resources were mainly distributed in Heilongjiang (15.0%), Hunan (12.5%), Jiangsu (10.0%), Hubei (9.9%), and Jiangxi (9.6%) in 2018. During 2013-2018, the annual average phosphorus inputs by straw incorporation in the main rice-cultivating provinces of China were 13.9-15.1 and 16.0-20.9 kg(P₂O₅)·hm^-2 for early rice and double cropping late rice, respectively. For medium and late rice, the annual average phosphorus inputs by straw incorporation reached as high as 19.3-29.3 kg(P₂O₅)·hm^-2. Nationally, the soil phosphorus inputs from straw incorporation were 14.4, 18.2, and 24.4 kg(P₂O₅)·hm^-2 for early rice, double cropping late rice, and medium and late rice, respectively. Based on the results of this study, the application rate of phosphate fertilizer in different rice-cultivating provinces should be adjusted according to the contribution of rice straw returning to the soil phosphorus input. This will help to maintain the soil phosphorus balance and reduce surplus phosphorus accumulation and phosphorus loss to surface water.