Abstract
Modern rice production systems need a reliable, easy-to-use, efficient, and environmentally-friendly method to determine plant nitrogen (N) status , predict grain yield, and optimize N management. We conducted field experiments to determine the influence of different N rates on Soil Plant Analysis Development (SPAD) readings of rice leaves. We also performed field validations to evaluate the grain yield and N use efficiency under recommended N rates. Our results showed that leaf SPAD readings increased as N rates increased. We applied the recommended N based on the relationships between the N rates and leaf SPAD readings at the tillering and booting stages. The recommended N decreased N rates and improved N use efficiency without sacrificing grain yield. When compared to farmer practices (FP), the recommended N rates of optimization (OPT) decreased by 5.8% and 10.0%, respectively. In comparison with FP, the N agronomic efficiency of OPT increased by 5.8 and 10.0% while the partial factor productivity of N increased by 6.0 and 14.2%, respectively. The SPAD meter may be a reliable tool to analyze the N in rice, estimate real-time N fertilization, and improve N use efficiency.
Highlights
Rice (Oryza sativa L.) is one of the most important cereal crops and food sources in the world
The N0 treatment resulted in the lowest leaf Soil Plant Analysis Development (SPAD) readings, while N270 showed the highest leaf SPAD readings in both years
In 2008, N270 leaf SPAD readings increased by 31.5–42.8% in experiment 1 and by 27.2–56.2% in experiment 2 when compared with N0
Summary
Rice (Oryza sativa L.) is one of the most important cereal crops and food sources in the world. N is arguably the most important limiting factor, aside from water, for rice production. Most farmers apply N in excess relative to the actual crop’s needs to harvest more grain. This practice leads to low N use efficiency due to high N losses through runoff, denitrification, leaching, volatilization, and a high risk of environmental contamination (Zeng et al, 2012; Liu et al, 2013; Bodirsky et al, 2014; Xiong et al, 2015). The average N use in China’s rice production has been reported to be
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