Abstract
Non-destructive assessment of plant nitrogen (N) status is essential for efficient crop production and N management in intensive rice (Oryza sativa L.) cropping systems. Chlorophyll meter (SPAD-502) has been widely used as a rapid, non-destructive and cost-effective diagnostic tool for in-season assessment of crop N status. The present study was intended to establish the quantitative relationships between chlorophyll meters readings, plant N concentration (PNC), N nutrition index (NNI), accumulated N deficit (AND), and N requirement (NR), as well as to compare the stability of these relationships at different vegetative growth stages in Japonica and Indica rice cultivars. Seven multi-locational field experiments using varied N rates and seven rice cultivars were conducted in east China. The results showed that the PNC and chlorophyll meters readings increased with increasing N application rates across the cultivars, growing seasons, and sites. The PNC and chlorophyll meters readings under varied N rates ranged from 2.29 to 3.21, 1.06 to 1.82 and 37.10 to 45.4 and 37.30 to 46.6, respectively, at TL and HD stages for Japonica rice cultivars, while they ranged from 2.25 to 3.23, 1.34 to 1.91 and 35.6 to 43.3 and 37.3 to 45.5 for Indica rice cultivars, respectively. The quantitative relationships between chlorophyll meters readings, PNC, NNI, AND, and NR established at different crop growth stages in two rice ecotypes, were highly significant with R2 values ranging from 0.69 to 0.93 and 0.71 to 0.86 for Japonica and Indica rice, respectively. The strongest relationships were observed for AND and NR at panicle initiation and booting stages in both rice ecotypes. The validation of the relationships developed in the present study with an independent data exhibited a solid model performance and confirmed their robustness as a reliable and rapid diagnostic tool for in-season estimation of plant N parameters for sustainable N management in rice. The results of this study will offer a suitable approach for managing N application precisely during the growth period of the rice crop in intensive rice cropping systems of east China.
Highlights
Nitrogen (N) is the most essential nutrients imperative for crop growth and productivity
For Japonica and Indica rice cultivars in Experiments 1, 3, 4, and 7, a higher N rate resulted in a higher plant N concentration (PNC) (Figure 1), PNC declined during advancing maturity (TL to HD)
This variability toward advancing maturity could be attributed to a decline in the fraction of total plant N associated with photosynthesis (Bélanger and Richards, 2000), change in leaf/stem ratio and self-shading of leaves (Yue et al, 2012)
Summary
Nitrogen (N) is the most essential nutrients imperative for crop growth and productivity. Effective in-season N management, both in terms of rate and timing of application is vital for improving crop productivity and quality as well as for sustaining soil fertility in rice (Oryza sativa L.) cropping systems (Ata-Ul-Karim et al, 2016). The excessive N application is the major cause of the lower N use efficiency in rice cultivation of China (Peng et al, 1996, 2006) and responsible for creating hazards for health, environmental sustainability and biodiversity (Liu et al, 2013; Bodirsky et al, 2014). The aforementioned issues have stirred much research effort aiming to develop efficient and sustainable N management strategies for improving the N use efficiency of the rice crop and environmental sustainability, especially in China
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
