Potential environmental benefits of substituting nitrogen and phosphorus fertilizer with usable crop straw in China during 2000–2017

Abstract

In order to meet growing food demand for the increasing population in China, chemical fertilizer has played a crucial role in increasing crop productivity in recent decades. However, the production of chemical fertilizer causes greenhouse gas (GHG) and atmospheric pollutant emissions, not to mention the effects of increased crop productivity, which creates a large mass of straw to be either burned or abandoned, leading to waste of resources, as well as GHG and atmospheric pollutant emissions. While many studies recognize the importance of substituting chemical fertilizer with straw as an organic alternative, little is known about the potential and spatiotemporal patterns in mitigating GHG and atmospheric pollutant through substituting chemical fertilizer with crop straw during the fertilizer production stage. We examine the potential impact of substituting straw for chemical fertilizer on the spatiotemporal pattern, and also examine the variation of both GHG and atmospheric pollutant emissions through using straw nutrient contents, emission factors, in combination with crop statistical data. Results show that, theoretically, accumulative nitrogen and phosphorus amounts from straw are estimated to be 55440.2 Gg and 16173.3 Gg, respectively, corresponding to 13.5% of total chemical nitrogen fertilizer and 11.5% of chemical phosphorus fertilizer. The substitution of chemical fertilizer with crop straw can mitigate 7088.8 Gg of GHG emissions, 19.9 Gg of NH3 emissions, 43.6 Gg of NOx emissions and 2.9 Gg of PM2.5 emissions annually. At the provincial level, Henan, Shandong, Sichuan, Hebei, Heilongjiang, Guangxi, Jiangsu and Anhui have the largest mitigation potential of GHG, NH3, NOx and PM2.5. High crop cultivation areas and yields in these provinces are the main cause of large emission mitigation. On the whole, the substitution of crop straw for chemical fertilizer is an effective measure to achieve crop waste utilization and to mitigate GHG, NH3, NOx and PM2.5 emissions. Finally, we propose three measures: innovation technologies for comprehensive straw utilization; multiple-channel financial support; and enhancing the awareness of resource recycling and environmental protection of farmers; as methods to promote straw-return, and thus achieve theoretical mitigation potential of GHG, NH3, NOx and PM2.5 emissions.