Fig. 4From: Rapid diagnosis of nitrogen status in rice based on Fourier transform infrared photoacoustic spectroscopy (FTIR-PAS)Linear regression between the total N concentration of rice leaves and the ratio of amide II to amide I. a The 2015 growth season for the first three stages only excluding the mature stage. b Only at the maturity from all growth seasons. c All growth stages in the 2015 season. d 2015, 2016, 2017 and 2018 growth seasons. The linear functions and the square of the Correlation Coefficient (R2) are shown in the each plotBack to article page