Abstract: A field experiment was conducted with potato under different nitrogen application levels (0, 120, 240, 300 and 360 kg·hm^-2) in Weining County, Bijie City, Guizhou Province from 2018 to 2019. In 2018, the canopy images of potato were obtained by digital camera at both tuber initiation stage and tuber bulking stage. The nitrogen nutrition indices of plants were measured. We analyzed the correlation between canopy digital parameters and nitrogen nutrition indices, screened the optimal canopy digital parameters for estimating nitrogen nutrition indices, and constructed the estimation model of nitrogen nutrition indices. The accuracy of the above equation model was verified and a 1∶1 linear relationship was drawn by using an independent nitrogen level experiment in 2019. The results showed that the ratio of redness intensity to blueness intensity (R/B) was better than other canopy parameters in characterizing nitrogen nutrition status of potato attuber initiation stage. R/B, the ratio of greenness intensity to blueness intensity (G/B), and the normalized blueness intensity (NBI) could characterize the nitrogen status of potato at tuber bulking stage, with R/B being the best. The correlation values (R²) between measured and estimated biomass and between measured and estimated nitrogen accumulation were 0.911 and 0.888, with RMSE being 0.685 and 25.115, and RE being 12.92% and 23.41%, respectively. The digital image processing technology can be used to evaluate and estimate nitrogen nutrition of potato. The best estimated period is tuber initiation stage and tuber bulking stage, the best estimation parameter is R/B, and the best model is linear regression equation.

Key words: potato, digital image, nitrogen, estimation, equation model, validation.