Problem to be solved: to provide a plant growth index calculating method, a plant growth index calculation program and a plant growth index calculation system capable of properly calculating a plant growth index representing the degree of growth in a plant.Controller andA reflected light measuring apparatus for measuring reflected light intensity of a measurement object having a plurality of leaves based on instructions of a control deviceA solar measuring apparatus for measuring the light intensity of sunlight based on instructions of a controllerIn a system containingReflected light measuring deviceFirst processing for measuring the reflected light intensity of the object to be measured with the first and second wavelengthsA solar measuring deviceA second processing for measuring the light intensity of sunlight at a third wavelength and a fourth wavelengthControl deviceUsing the reflected light intensity information obtained from the reflected light measuring instrument and the light intensity information of the solar light obtained from the solar measuring instrument.The third step to calculate plant growth index which shows the degree of growth in the measurement object andAndIn the third process,Based on the correction information about at least one of the fields to be measured and the subject to be measuredThe reflected light intensity of the object to be measured is corrected.Plant growth index is calculated.植物における生育の度合いを表す植物生育指標を適切に算出することができる植物生育指標算出方法、植物生育指標算出プログラム及び植物生育指標算出システムを提供する。制御装置と、制御装置の指示に基づいて複数の葉を持つ測定対象の反射光強度を測定する反射光測定装置と、制御装置の指示に基づいて太陽光の光強度を測定する太陽光測定装置と、を含むシステムにおいて、反射光測定装置が、第１波長及び第２波長で測定対象の反射光強度を測定する第１処理と、太陽光測定装置が、第３波長及び第４波長で太陽光の光強度を測定する第２処理と、制御装置が、反射光測定装置から取得した測定対象の反射光強度情報と太陽光測定装置から取得した太陽光の光強度情報とを用いて、測定対象における生育の度合いを表す植物生育指標を算出する第３処理と、を実行し、第３処理では、測定対象及び測定対象を生育する圃場のうち少なくとも一方に関する補正情報に基づいて、測定対象の反射光強度を補正して、植物生育指標を算出する。
