13.4 Methods to Improve NUE in China’s Agricultural
Systems
13.4.1 Nitrogen Use Efficiency of China’s Agricultural
Systems
Generally, NUE can be express as the yield produced per unit of N applied (Cui et al.
2014b). Although large amount of N fertilizer has been applied to croplands, less
than 50% of the Nr input is converted into harvested products, compared to that
during the early 1960s (Lassaletta et al. 2014). Moreover, field experiments have
shown that the percentage of in-season N fertilizer recovery ranged from 30% to
35% in the 1990s in China (Zhu and Chen 2002). NUE has varied throughout history
in China. It increased from 40 Æ 3% to 45 Æ 3% from 1980 to 1984, decreased to
36 Æ 2% in 2003, and increased to 39 Æ 2% in 2010 (Gu et al. 2017). Specifically,
the NUE of vegetable cropping systems was lower than the average NUE of the three
major crops. For example, the NUE of an open-air system was 25.9 Æ 13.3% (Ti et al.
2015). The kilogram of harvested product per kilogram of N applied for the three
major crops markedly decreased from 1979 to 2008 (Wu et al. 2016).
13.4.2 Measures to Increase NUE
Improving NUE is one of the most effective ways to increase crop productivity while
reducing environmental degradation (Zhang et al. 2015). China’s NUE was lower
than that in other regions such as North America and Europe (Ladha et al. 2005;
Lassaletta et al. 2014; Zhang et al. 2015). Achieving food and environmental
security in the near future is imperative and urgent in China. Therefore, it is
important to improve NUE in China. Furthermore, Zhang et al. (2015) indicated
that China’s NUE still has not passed the turning point of the environmental Kuznets
curve, which means that it is possible to increase NUE in China by using N reduction
mitigations.
Farm-scale technologies and management practices are required to improve the
NUE in China. Strategies such as improvements in irrigation and fertilizer management and the use of inhibitors could reduce N loss and improve crop productions.
Furthermore, regular attention should be paid to establishing national and local
targets and policies. Measures to improve NUE have been widely conducted in
China. Measures such as the integrated soil-crop system management (ISSM) led by
China Agricultural University could significantly increase the crop grain yield by
18.1–35.2%, while reducing N application rate by 3.8–14.4% compared to farmer’s
current practice, which indicates a higher improvement in NUE (Chen et al. 2014).
Additionally, knowledge-based N management, including controlled-release N fertilizer application, nitrification and urease inhibitors, higher N fertilizer application
splitting frequencies, lower basal N fertilizer proportions, deep placement of N
304
C. Ti and X. Yan
Systems
13.4.1 Nitrogen Use Efficiency of China’s Agricultural
Systems
Generally, NUE can be express as the yield produced per unit of N applied (Cui et al.
2014b). Although large amount of N fertilizer has been applied to croplands, less
than 50% of the Nr input is converted into harvested products, compared to that
during the early 1960s (Lassaletta et al. 2014). Moreover, field experiments have
shown that the percentage of in-season N fertilizer recovery ranged from 30% to
35% in the 1990s in China (Zhu and Chen 2002). NUE has varied throughout history
in China. It increased from 40 Æ 3% to 45 Æ 3% from 1980 to 1984, decreased to
36 Æ 2% in 2003, and increased to 39 Æ 2% in 2010 (Gu et al. 2017). Specifically,
the NUE of vegetable cropping systems was lower than the average NUE of the three
major crops. For example, the NUE of an open-air system was 25.9 Æ 13.3% (Ti et al.
2015). The kilogram of harvested product per kilogram of N applied for the three
major crops markedly decreased from 1979 to 2008 (Wu et al. 2016).
13.4.2 Measures to Increase NUE
Improving NUE is one of the most effective ways to increase crop productivity while
reducing environmental degradation (Zhang et al. 2015). China’s NUE was lower
than that in other regions such as North America and Europe (Ladha et al. 2005;
Lassaletta et al. 2014; Zhang et al. 2015). Achieving food and environmental
security in the near future is imperative and urgent in China. Therefore, it is
important to improve NUE in China. Furthermore, Zhang et al. (2015) indicated
that China’s NUE still has not passed the turning point of the environmental Kuznets
curve, which means that it is possible to increase NUE in China by using N reduction
mitigations.
Farm-scale technologies and management practices are required to improve the
NUE in China. Strategies such as improvements in irrigation and fertilizer management and the use of inhibitors could reduce N loss and improve crop productions.
Furthermore, regular attention should be paid to establishing national and local
targets and policies. Measures to improve NUE have been widely conducted in
China. Measures such as the integrated soil-crop system management (ISSM) led by
China Agricultural University could significantly increase the crop grain yield by
18.1–35.2%, while reducing N application rate by 3.8–14.4% compared to farmer’s
current practice, which indicates a higher improvement in NUE (Chen et al. 2014).
Additionally, knowledge-based N management, including controlled-release N fertilizer application, nitrification and urease inhibitors, higher N fertilizer application
splitting frequencies, lower basal N fertilizer proportions, deep placement of N
304
C. Ti and X. Yan