Monitoring plant nitrogen accumulation with different canopy spectrometers at early growth stages in rice

The objective of this paper is to quantify the relationship between plant nitrogen accumulation (PNA) and canopy spectral reflectance at early growth stages in rice, and provide a technical support for decision making on nitrogen dressing management. Based on seven field experiments with different rice cultivars and nitrogen rates in five different growing seasons, the canopy spectral reflectance during the stages of tillering and elongation were measured with three different canopy spectral sensors (Fieldspec FR 2500, MSR-16 and GreenSeeker RT 100), and the plants were sampled for PNA measurement simultaneously. Then the relationships beween PNA and vegetation indices were analyzed. The results showed that some vegetation indices were closely related to PNA, but there were significant differences among the estimation models based on different canopy sensors. For the hyperspectral sensor (Fieldspec FR 2500), DVI(760, 740) had a good performance on model development, with determination coefficient (R2) of 0.79, but the performance of model testing was poor, with R2 and RMSE of 0.15 and 2.11 g/m2, respectively. For the multispectral sensor (MSR-16), DVI(760, 710) could be used for PNA estimation, with R2 of 0.94 for model development, and with R2 and RMSE of 0.94 and 0.76 g/m2 for model testing, respectively. NDVI(770, 660) from the active spectral sensor (RT 100) gave the best estimation of PNA, with R2 of 0.97 for model development, and with R2 and RMSE of 0.97 and 0.62 g/m2 for model testing, respectively. These results would be helpful for selection of proper spectral sensors in PNA monitoring during early growth stages of rice.