Estimation of weekly radiation-use efficiency of maize under potential production conditions

The aim of this study is obtaining continuous weekly values of maize RUE by novel in-situ measurements of radiation. A semi-maturing cultivar of maize was cultivated in University of Tehran research farm in Karaj. Dry biomass and leaf area index were measured during 15 consecutive weeks of growing season. Then, based on in-situ complete pyrheliometry, by using insulation simulation and image processing, daily average of maize canopy reflectivity, extinction coefficient and the absorbed visible light of the canopy were estimated using a multi-layer model. During growing season infield continuous measurement of full spectrum irradiation, was measured continuously by TSR for all daylight hours. The diurnal insolation was simulated for that plant by an angular scanner (illuminator) during night time between 21:00 to 21:30 hrs. By applying an image processing technique, the visible band reflectivity of maize cover was estimated for the first seven weeks of study period. The measurements were continued till full closure of canopy and 12 different weekly values of RUE were calculated using the field measured data. The proposed approach allows generating continuous graph of RUE values. The research results indicate that even in the potential production conditions, using a constant value of radiation use efficiency for entire growing season of maize is not possible. During the growing season, the range of maize radiation-use efficiency reached 36.1 g/MJ, but the weekly values median of this quantity was equal to 3.5 g/MJ, which its occurrence probability in half of the growing season is 100%.