Novel technique for non-destructive LAI estimation by continuous measurement of NIR and PAR in rice canopy

Although leaf area index (LAI) is a useful index of crop growth, evaluating LAI by destructive sampling is laborious and time-consuming. In the present study, we developed a novel technique to determine rice LAI nondestructively and accurately throughout growth period in paddy field. Near-infrared radiation (NIR) and photosynthetically active radiation (PAR) were measured by a pair of optical sensors inside and outside rice canopy at 1-min intervals. Simple ratio (SR) and NIR to PAR ratio (N/P) were measured depending on growth stage, and the criteria to extract valid SR and N/P that represent LAI accurately were determined. SR and N/P obtained under cloudy conditions were found to represent LAI with high accuracy (R2 = 0.91), and seasonal dynamics of canopy growth curves were successfully drawn for two rice cultivars at two experimental fields. Mathematical analysis revealed that not cumulative PAR but cumulative temperature could trigger exponential canopy growth. The present technique can be used as a powerful tool for evaluating, modelling, and phenotyping crop growth characteristics in various rice cultivars as well as other crops.

Automated summary

A new technique was developed to nondestructively determine rice LAI by measuring NIR and PAR with optical sensors and calculating SR and N/P ratios based on growth stages. This technique successfully drew seasonal canopy growth curves, and can be used as a powerful tool for evaluating, modeling, and phenotyping crop growth characteristics in various rice cultivars as well as other crops.