Yulong Yin, Rongfang Zhao, Yi Yang, Qingfeng Meng, Hao Ying, Kenneth G. Cassman, Wenfeng Cong, Xingshuai Tian, Kai He, Yingcheng Wang, Zhenling Cui, Xinping Chen, and Fusuo Zhang

PNAS September 28, 2021 118 (39) e2106576118

Significance

Smallholder farmers in China tend to overuse N fertilizer as an “insurance” to avoid yield loss. Better management can be achieved but lack resources to adopt advanced technologies that improve N use efficiency. Our study proposes a simplified but effective N management approach without sampling. This new approach based on steady-state N balance could significantly reduce N fertilizer use while maintaining or even increasing yields compared to the local farmers’ practice. Demonstrations in Chinese cereal production indicate the potential of the new N management approach to become an effective tool for policy guidance and to contribute to global N sustainability.

Abstract

Hundreds of millions of smallholders in emerging countries substantially overuse nitrogen (N) fertilizers, driving local environmental pollution and global climate change. Despite local demonstration-scale successes, widespread mobilization of smallholders to adopt precise N management practices remains a challenge, largely due to associated high costs and complicated sampling and calculations. Here, we propose a long-term steady-state N balance (SSNB) approach without these complications that is suitable for sustainable smallholder farming. The hypothesis underpinning the concept of SSNB is that an intensively cultivated soil–crop system with excessive N inputs and high N losses can be transformed into a steady-state system with minimal losses while maintaining high yields. Based on SSNB, we estimate the optimized N application range across 3,824 crop counties for the three staple crops in China. We evaluated SSNB first in ca. 18,000 researcher-managed on-farm trials followed by testing in on-farm trials with 13,760 smallholders who applied SSNB-optimized N rates under the guidance of local extension staff. Results showed that SSNB could significantly reduce N fertilizer use by 21 to 28% while maintaining or increasing yields by 6 to 7%, compared to current smallholder practices. The SSNB approach could become an effective tool contributing to the global N sustainability of smallholder agriculture.

See: https://www.pnas.org/content/118/39/e2106576118

Fig. 1. The N cycle in soil–crop system. N flows include major inputs, outputs, and pools of organic and inorganic (3). The long-term fate of external N inputs includes crop N uptake (crop removal plus N return), inevitable N loss, and overapplied N.