Nitrogen deficiency induced a decrease in grain yield related to photosynthetic characteristics, carbon–nitrogen balance and nitrogen use efficiency in proso millet (Panicum miliaceum L.)

ABSTRACT

Field experiments involving proso millet (Panicum miliaceum L.) cultivar under four nitrogen (N) levels (N0, N60, N105 and N150) were conducted in 2015 and 2016 to explore the decrease in grain yield under N deficiency related to the changes in leaf photosynthetic characteristics, carbon (C)–N balance and N use efficiency. Results showed that N deficiency decreased the net photosynthesis rate, stomatal conductance, transpiration rate and chlorophyll content and increased the intercellular CO₂ concentration of proso millet flag leaves from flowering to maturity. N deficiency negatively regulated the C–N balance and increased the C/N ratio by reducing the total N, soluble protein and soluble sugar contents, resulting in high starch content. N uptake and utilisation were significantly reduced because of less available N. Significantly positive correlations were observed between the grain yield and photosynthetic characteristics or N use efficiency, whereas a negative correlation was found between the grain yield and the C/N ratio. The yields generated by N0, N60 and N105 were lower than that of N150 in both years. The N fertiliser regression formulae developed in the study would provide useful information about the N fertiliser rate of proso millet.

KEYWORDS:

• Carbon–nitrogen balance
• grain yield
• nitrogen deficiency
• photosynthetic characteristics
• proso millet

Acknowledgments

The authors gratefully acknowledge the support received from the Yulin Academy of Agricultural Science. We also thank the local peasants for preparing and participating in this study.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

The research was supported by the National Millet Crops Research and Development System (CARS–13.5–06–A26), National Science and Technology Supporting Plan (2014BAD07B03), National Natural Science Foundation of China (31371529), and Minor Grain Crops Research and Development System of Shaanxi Province (NYKJ–2018–YL19).