Temporal and spatial distribution characteristics of rice stalk resources and its potential of synthetic fertilizers substitution returning to farmland in China from 1988 to 2018

Rice stalk resource in China is plentiful, but in different regions the rice stalk resources, the corresponding nutrient resources and synthetic fertilizers substitute potential through rice stalk incorporation as well as the changes over time have not been very clear. Based on the long-term monitoring data of rice from 1988 to 2018 of the Ministry of Agriculture and Rural Affairs in China's rice-growing areas, this study analyzed the amount of rice stalk and its nutrient resources and synthetic fertilizers substitute potential through rice stalk incorporation in different years in each region of China, aiming to provide basis for rational utilization of rice stalk resources. The results showed that the annual average amount of rice stalk resources and NPK resources reached 1.69×108 t and 452.09×104 t respectively during 2009-2018, which increased by 0.23×108 t and 61.50×104 t compared with 1988-1998, with the highest increase in North-East (NE). The annual average amount of rice stalk resources and NPK resources increased with planting years. In the first stage (1990s-2000s) and the second stage (2000s-2010s), the annual changing rate (ACR) of rice stalk resources were 18.11×104 t/a and 211.47×104 t/a, and the ACR of nutrient resources were 0.15×104 t/a of N, 0.02×104 t/a of P, 0.31×104 t/a of K and 1.76×104 t/a of N, 0.25×104 t/a of P, 3.66×104 t/a of K, respectively. There were more than 70% of rice stalk and its nutrient resources distributed in Yangtze River Delta (YRD), Middle of the Yangtze River (MYR) and South-west (SW), with the highest in YRD (4.15×107 t, 111.05×104 t of NPK) and the lowest in South China (SC) (2.20×107 t, 58.54×104 t of NPK). The rice stalk NPK nutrient returning to farmland per unit cultivated land area has increased continually during 1988-2018, accounting for 10.88%-12.53%, 11.83%-17.13%, 116.22%-122.62% of the annual fertilizer application, respectively. The annual average synthetic fertilizers substitution through rice stalk incorporation were (28.90±0.14) kg/hm2 of N, (5.80±0.03) kg/hm2 of P and (180.46±0.52) kg/hm2 of K in China, with the highest in YRD ((34.44±0.20) kg/hm2 of N, (6.91±0.04) kg/hm2 of P, (129.23±0.74) kg/hm2 of K), and the lowest in SC ((25.80±0.23) kg/hm2of N, (5.18±0.05) kg/hm2 of P and (96.83±0.87) kg/hm2 of K). Therefore, making full use of rice stalk resources could be an important guarantee for reducing fertilizer application and increasing fertilizer use efficiency.