Validation of the leaf area index estimated using the extinction coefficient of photosynthetically active radiation in soybean

Techniques to monitor vegetation cover have been used to track the biomass and yield of agricultural crops. Quantifying the leaf area index (LAI) and its variation throughout the production cycle of soybean is important because this data can be used as an input variable in growth and productivity models. Field experiments were carried out during the 2017/2018 and 2018/2019 growing season in soybean crops at the Faculdade Marechal Rondon (FARON) in Vilhena, RO, Brazil, to measure the LAI of cultivar 75I77 RSF IPRO from the estimated extinction coefficient of photosynthetically active radiation (PAR). LAI measurements were performed weekly in the 2018/2019 crop season. The PAR data were collected using the PAR Apogee® SQ-316-S linear sensor. The light extinction coefficient (Kc) was calculated using LAI and solar radiation interception data. A Kc value of 0.687 was found for this crop, indicating that more than 68% of the light was intercepted by the plant structure. In addition, the LAI data estimated via Kc were compared with LAI values estimated with the CROPGRO-Soybean model. The first method estimated the LAI values better than the second, as the r² increased from 0.738 to 0.882, the difference was reduced from 19.9 to 13.3%, and the d-value changed from 0.815 to 0.952. Thus, the extinction coefficient method of PAR can efficiently estimate the LAI parameter in soybean.