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Accurate estimations of the vertical leaf nitrogen (N) distribution within a rice canopy is helpful for understanding the nutrient supply and demand of various functional leaf layers of rice and for improving the predictions of rice productivity. A two-year field experiment using different rice varieties, N rates, and planting densities was performed to investigate the vertical distribution of the leaf nitrogen concentration (LNC, %) within the rice canopy, the relationship between the LNC in different leaf layers (LNC Li , i = 1, 2, 3, 4), and the relationship between the LNC Li  and the LNC at the canopy level (LNC Canopy ). A vertical distribution model of the LNC was constructed based on the relative canopy height. Furthermore, the relationship between different vegetation indices (VIs) and the LNC Canopy , the LNC Li , and the LNC vertical distribution model parameters were studied. We also compared the following three methods for estimating the LNC in different leaf layers in rice canopy: (1) estimating the LNC Canopy  by VIs and then estimating the LNC Li  based on the relationship between the LNC Li  and LNC Canopy ; (2) estimating the LNC in any leaf layer of the rice canopy by VIs, inputting the result into the LNC vertical distribution model to obtain the parameters of the model, and then estimating the LNC Li  using the LNC vertical distribution model; (3) estimating the model parameters by using VIs directly and then estimating the LNC Li  by the LNC vertical distribution model. The results showed that the LNC in the bottom of rice canopy was more susceptible to different N rates, and changes in the LNC with the relative canopy height could be simulated by an exponential model. Vegetation indices could estimate the LNC at the top of rice canopy. R 705 /(R 717 +R 491 ) (R 2  = 0.763) and the renormalized difference vegetation index (RDVI) (1340, 730) (R 2  = 0.747) were able to estimate the parameter “a” of the LNC vertical distribution model in indica rice and japonica rice, respectively. In addition, method (2) was the best choice for estimating the LNC Li  (R 2  = 0.768, 0.700, 0.623, and 0.549 for LNC L1 , LNC L2 , LNC L3 , and LNC L4 , respectively). These results provide technical support for the rapid, accurate, and non-destructive identification of the vertical distribution of nitrogen in rice canopies.

Estimation of Vertical Leaf Nitrogen Distribution Within a Rice Canopy Based on Hyperspectral Data