Crop Reflectance as a tool for the online monitoring of LAI and PAR interception in two different greenhouse Crops

Methods for the online monitoring of Leaf Area Index (LAI) and photosynthetically active radiation (PAR) interception of the canopy, in greenhouse conditions, using reflectance measurements of the PAR part of the spectrum for tomato and sweet pepper were investigated. LAI and PAR interception were measured at the same moments as reflectance at six wavelengths at different plant developmental stages in greenhouses. The normalised difference vegetation index (NDVI) was also calculated. Relationships between the measured parameters were established in experimental greenhouses and subsequently tested in commercial greenhouses. The best estimates for LAI and PAR interception for both tomato and sweet pepper were obtained from reflectance at 460 nm. The goodness of the fit was validated with data from the commercial greenhouses was also tested. The divergence of the results from those reported from field experiments can be explained by the special environment that occurs in the greenhouse, where there are more sources of reflectance due to the greenhouse frame and the white plastic that covered the floor. Thus, this new approach to estimating LAI and PAR interception using 460 nm is promising and could play a role in the decision support systems that are used in modern greenhouse management.

Research highlights
► Reflectance offer a non-destructive method for estimating PAR interception and LAI
► Reflectance at 460 nm gives good prediction of PAR interception and LAI
► NDVI not a robust predictor of LAI and PAR interception under greenhouse conditions