Monthly intercepted photosynthetically active radiation estimation based on the Beer-Lambert’s law across the cereal crops of Castilla y León (Spain)

Agriculture is by far the most important economic activity in the Spanish autonomous region of Castilla y Leon. ´ Numerous factors influence crop development but one of the most related variables to the photosynthetic process is Photosynthetically Active Radiation (PAR). Estimating Intercepted Photosynthetically Active Radiation (IPAR) in different crops through the Beer-Lambert law could be a relevant factor in crop season planning by enabling photosynthesis monitoring. The Beer-Lambert Law is applied in this study to the data for almost 2 million hectares of wheat, barley, and maize cultivated in Castilla y Leon ´ in 2021. The fourteen-year data set of Global Horizontal Irradiance (GHI) used to calculate the monthly PAR data in the region was collected at 93 meteo rological stations (46 in Castilla y Leon ´ and 47 in neighboring Spanish and Portuguese regions). Two previously published global calibrated models were employed to calculate the PAR, with a relative Root Mean Square Error (rRMSE) below 6%, for the measured daily mean values of PAR in Burgos. Processing the various NASA Terra and Aqua satellite images yielded the monthly Leaf Area Index (LAI) and the literature review provided the light extinction coefficient (k). The Geographic Information System (GIS) facilitated visualization of IPAR estimates for the three cereal crops in all months of its growing season. Wheat and barley reach their IPAR peaks in June and July, while maize peaks in July and August. In addition, the fraction of Intercepted Photosynthetically Active Radiation (fIPAR) was calculated in different provinces to assess PAR interception for each cereal at different growing stages. In June, almost 50% of the wheat area in Burgos, Palencia and Soria displayed fIPAR values exceeding 45% while in the case of barley only the province of Burgos reached these percentages of area and.fIPAR.

This research forms part of project TED2021-131563B-I00, funded by MCIN/AEI/ 10.13039/501100011033 and by the “European Union NextGenerationEU/PRTR”. Elena Garrachón-Gómez expresses her thanks to the Universidad de Burgos for the funding of her pre-doctoral contract. Ignacio García is likewise grateful to the Spanish Ministry of Universities and the European Union-Next Generation EU for their financial support (Program for the requalification of the Spanish university system 2021-2023, Resolution 1402/2021).