Evaluating a new leaf fluorescence sensor for estimating rice nitrogen status

Real-time non-destructive diagnosis of crop nitrogen (N) status is crucially important for the success of in-season site-specific N management. Chlorophyll meter (CM) has been commonly used to non-destructively estimate crop leaf chlorophyll concentration, and indirectly estimate crop N status. Dualex 4 is a newly developed leaf fluorescence sensor that can estimate both leaf chlorophyll concentration and polyphenolics, especially flavonoids. The ratio of chlorophyll and flavonoid concentration, which is termed N balance index (NBI), has been reported to be more sensitive to crop N status than SPAD meter readings. So far, no studies have been reported to evaluate this new sensor for estimating rice N status. Therefore, the objective of this study was to compare the accuracy of Dualex 4 sensor and chlorophyll meter SPAD-502 for estimating the N nutritional status of rice in Northeast China. A field experiment involving five N application rates (0, 70, 100, 130, 160 kg N ha^-1), two cultivars (Longjing 21 and Kongyu 131) and three replications was conducted in Jiansanjiang, Heilongjiang Province, China in 2013. Leaf and plant samples were collected at three key growth stages and analyzed for chlorophyll and N concentrations. The preliminary results indicated that both instruments could explain over 80% of variation of leaf chlorophyll concentration. Their ability to estimate leaf N concentration was influenced by rice cultivars and growth stages. Across cultivars and growth stages, Dualex 4 and SPAD meter-based indices only explained about 30% of variation of leaf N concentration. Although flavonoid was negatively correlated with leaf N concentration (R²=0.172, p=0.0002), the new index NBI (Chlorophyll/Flavonoid) did not significantly improve the accuracy of estimating leaf N concentration as compared with SPAD meter. More studies are needed to further evaluate the Dualex 4 leaf fluorescence sensor for estimating rice N status and determine its p- tential benefits over SPAD meter.