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Light-based analysis is a fundamental approach to quantify the effects of factors determining crop growth in a given environment. The objectives of this study are to confirm the applicability of a digital imagery technique to extract green leaf areas for estimating light interception (LI) of maize canopy and to understand the effect of fertilizer application on the LI and radiation use efficiency (RUE) of maize under various agro-environments in Northern Mozambique. A locally recommended variety, Matuba, was grown in a single season with three different N application rates (0, 30, and 80 kgN ha(-1)) at one hot/dry low-elevation site, two hot/humid mid-elevation sites, and one cool/humid high-elevation site. Repeated measurements with quantum sensors revealed that the digital imagery is applicable to estimate the LI of maize except for leaf-senescing period close to maturity. The N application demonstrated profitable yield increases with agronomic nitrogen use efficiencies (kg grain yield per kg N input) of 20.6-35.3 kg kg(-1) except for the low-elevation site with severe drought stress. In the mid-elevation sites, the yield increases were mostly explained by the improvement of RUE while the effect on LI was small because the vegetative growth was naturally vigorous under high temperatures irrespective of N inputs. At the high-elevation site, the N application improved its stagnant initial canopy development and increased both RUE and LI. The simple and inexpensive imagery technique should be useful to identify physiological basis of maize responses to fertilizer application and its interaction with regional environment even under poorly equipped regions in the tropics.