An estimate of greenhouse gas (N2O and CO2) mitigation potential under various scenarios of nitrogen use efficiency in Chinese croplands

It is well recognized that improving nitrogen use efficiency (NUE) can directly reduce nitrous oxide (N2O) emission in cropland and indirectly reduce carbon dioxide (CO2) release from nitrogen (N) production, while such a reduction has not been well quantified in China. We estimated the greenhouse gas (GHG; N2O and CO2) mitigation potential (MP) from Chinese cropland and its regional distribution by quantifying NUE and determining the amount of over-applied synthetic N under various scenarios of NUE. We estimated that synthetic NUE in the late 1990s was 31 +/- 11% (mean +/- SD) for rice, 33 +/- 13% for wheat, and 31 +/- 11% for maize cultivation. Improving NUE to 50% could cut 6.6 Tg of synthetic N use per year, accounting for 41% of the total used. As a result of this reduction, the direct N2O emission from croplands together with CO2 emission from the industrial production and transport of synthetic N could be reduced by 39%, equivalent to 60 Tg CO2 yr-1. The MP was probably underestimated because organic N supply was not taken into account when estimating NUE. It was concluded that improving N management can greatly reduce GHG (N2O and CO2) emissions in Chinese croplands, and mitigation in the Jiangsu, Henan, Shandong, Sichuan, Hubei, Anhui, and Hebei provinces should be given priority.