Estimation of Nitrogen Nutrition Index By SPAD Value of Top Leaves in Rice.

Abstract: Rapid, non-destructive and accurate estimation of crop nitrogen (N) nutrition status is essential for acquiring timely and inexpensive information for crop management and grain yield prediction£®This study was endeavored to examine the relationships between N nutrition index (NNI) and SPAD values and the relative SPAD index (RSPADi) values of the top first, second and third leaves. Three field experiments were conducted with varied N rates (0-375 kg N ha-1) using three rice (Oryza sativa L.) cultivars, Lingxiangyou-18 (LXY-18), Wuxiangjing-14 (WXJ-14) and Shanyou-63 (SY-63) in Jiangsu province of east China. Five hills from each experimental plot were sampled from active tillering to heading for growth analysis. The results showed that, the SPAD value and NNI increased with increasing N application rates. In contrast, RSPADi values decreased with increasing N application rates. The SPAD values for different leaf positions showed a significant positive relationship with NNI; however, the relationship varied across the years, cultivars and different growth stages having the correlation coefficient R2 ranging from 0.61 to 0.988. Relationship between RSPADi at different leaf positions was stable across the years, cultivars and different growth stages and NNI having the correlation coefficient R2 ranging from 0.65 to 0.99. The relationships between RSPAD1 and NNI from mid-tillering to stem elongation stage were (y = 3.2461x-2.2493, R2 = 0.6612, y = 2.9776x-1.9484, R2 = 0.9511 and y = 1.7828x - 0.7933, R2 = 0.808) and from panicle initiation stage to heading stage were (y = 2.5625x-1.6177, R2 = 0.7467, y = 5.194x-4.2063£¬R2 = 0.8961 and y = 4.7367x-3.6856, R2 = 0.9161) for the top first, second and third leaf respectively. These results indicated that at the same leaf position, RSPADi was superior to the SPAD values in the correlation with NNI; however, comparison between the different leaf positions revealed that the second leaf¡¯s RSPAD2 has the highest correlation coefficient among the top 3 fully expanded leaves. The strongest correlation between NNI and RSPAD2 could be used for quantitative estimation of in-season N nutrition status of rice in east China. Keywords: Rice; nitrogen nutrition index (NNI); SPAD; relative SPAD index (RSPADi); diagnosis;