A B S T R A C TThe Leaf Area Index (LAI) is a key parameter to evaluate the vegetation spectral response, estimating plant nutrition and water requirements. However, in large fields is difficult to obtain accurate data to LAI determination. Therefore, the objective of this study was the estimation of LAI, biomass and yield of irrigated cotton through digital hemispherical photography. The treatments consisted of four nitrogen doses (0, 90, 180 and 270 kg ha ). Digital hemispherical photographs were collected under similar sky brightness conditions at 60 and 75 days after emergence (DAE), performed by the Digital Plant Canopy Imager -CI-110® of CID Inc. Biomass and LAI measurements were made on the same dates. LAI was also determined by destructive and non-destructive methods through a leaf area integrator (LI-COR® -LI-3100C model), and by measurements based on the midrib length of all leaves, respectively. The results indicate that the hemispherical images were appropriate to estimate the LAI and biomass production of irrigated cotton, while for the estimation of yield, more research is needed to improve the method.Estimativa de variáveis biofísicas do algodoeiro por meio de fotografia hemisférica R E S U M O O Índice de Área Foliar (IAF) é um parâmetro essencial na avaliação da resposta espectral da vegetação e estimativa das necessidades nutricionais e hídricas das culturas, porém é difícil obter sua estimativa de forma rápida e precisa em grandes áreas. O objetivo deste estudo foi a estimativa do IAF, da biomassa aérea e da produtividade do algodoeiro irrigado por meio de fotografia hemisférica digital. O experimento consistiu de uma combinação fatorial de quatro doses de nitrogênio (0, 90, 180 e 270 kg ha -1 ) e quatro de fósforo (0, 120 e 240 e 360 kg ha -1