Abstract:

【Objective】Establishment of the nitrogen uptake diagnosis model for early rice based on NDVI, and recommend- ation of the N topdressing rate. 【Method】 The quantitative relationship between canopy NDVI and plant nitrogen uptake (PNU) was studied using the data of field experiment with different N treatments, and the models were tested using independent experiment data. The optimum diagnosis model was established to recommend the N topdressing rate with canopy NDVI. Then the recommended N rate, grain yield and nitrogen use efficiency (NUE) were compared with those of farmer’s N management treatment.【Result】 Rice canopy NDVI was well positive correlated with PNU at key development stage, the correlation for single stage was better than whole stage, and exponential curve better fitted the relation than linear function, the same for the test results with independent experiment data. The prediction precision of PNU diagnosis model at tillering and jointing stages was 0.907 and 0.941, respectively. Compared with the farmer’s N management, equivalent grain yield was obtained with reduced N rate while NUE was improved. The error between the N rate of spectral diagnosis fertilization and the optimum N rate calculated with the N-yield curve was 2.12% at high transplanting density and -2.22% at low transplanting density, respectively, while the error for grain yield was -0.75% and -5.04%, respectively. 【Conclusion】 Spectral diagnosis fertilization mode can reduce nitrogen application rate and raise nitrogen use efficiency on premise of grain yield, and has a potential to be widely applied in rice N management.

Key words: rice, NDVI, plant nitrogen uptake (PNU), recommend fertilization, grain yield