Non-disruptive evaluation of leaf area index using diffused light sensor for tomato cultivation.

Abstract

A diffused light sensor was developed to evaluate the leaf area index (LAI) of tomato plant canopy in a greenhouse non-disruptively. This sensor was simply designed with the addition of a silicon photo diode attached to the inside of a black shading frame (100 mm × 100 mm × 100 mm) in order to screen the photodiode from direct solar radiation. The openings of the sensor in the northern direction were set inside and outside of the plant canopy to measure light intensity (PL: inside of the plant canopy, PU: outside of the plant canopy). The light intensity (PU), as measured by the sensor in the greenhouse , changed in a similar pattern to that of solar radiation outside the greenhouse without influence from shadings such as steel frames and covering materials in the greenhouse. The relative light intensity (RLI (%) = PL / PU × 100) in triple-truss tomato cultivation showed a steady value during daytime. Regardless of cultivation conditions (e.g. season, the amount of nitrate supply), the RLI after planting decreased with increasing tomato L A I, and a negative correlation between natural logarithm of Avg. R LI (ln(Avg. RLI)) and LAI was observed. These results suggested that diffused light sensors can be used to non-disruptively evaluate of the LAI of tomato plant canopy in greenhouse .