Estimation of the Fraction of Light Interception of Soybean Communities using Handheld NDVI Sensor

Abstract

We compared methods of measuring the normalized difference vegetation index (NDVI) with a handheld NDVI sensor (GreenSeeker Handheld Crop Sensor) in estimating the fraction of light interception of the soybean community. Soybeans were planted at the densities of 2, 5, 10, 15, and 30 plants m⁻² in Yamaguchi Prefecture in 2019. There are two methods of measurement: the wiper method that intersects the ridges and the linear method that measures only the ridges. NDVI was measured nine times from the establishment of seedlings to the seed filling stage. On the same day, the fraction of light interception was measured using a photosynthetic active radiation sensor. Estimation of the fraction of light interception from NDVI showed that the error was smaller in the wiper method than in the linear method. The radiation use efficiency (RUE) was calculated using the fraction of light interception estimated from NDVI, and it was compared with RUE calculated from the measurement value. RUE of the wiper method corresponded with measured RUE, while RUE of the linear method was less than measured RUE for all the planting densities except 2 plants m⁻². These results indicate that the wiper method is more accurate than the linear method when estimating the fraction of light interception from NDVI measured with a handheld NDVI sensor in soybean communities.