Changes Of Nitrogen Distribution And Rapid Diagnosis For Nitrogen Nutrition Status In The Canopy Leaf Of Rice

Nitrogen (N) is one of the most important nutritional elements to promote rice growth and development. Rational application of N fertilizer can increase the rice yield, decrease loss of N fertilization and reduce the production cost and environmental pollution. In this work, we have combined SPAD (Soil Plant Analysis Development) meter, a fast, convenient, non-destructive and low cost diagnosis tool, with traditional diagnosis method for N nutrition. Through the analysis of dynamic regression between them, we attempted to replace the traditional diagnosis by SPAD meter. This work could provide an important theoretical basis and practical guidance for N nutrition diagnosis and further improve the rice efficiency of N utilization and the yield.On the basis of analyzing various literatures, we have investigated the characteristic change, the distribution and the internal and external factors of SPAD values in the rice canopy through two-year field experiments (six N levels) and one-year net room experiments (five N levels). The study highly focused on various factors on the SPAD values and the regression relationships between SPAD values and leaf N concentration in the canopy, nitrogen nutrition index (NNI) and chlorophyll fluorescence, respectively. The main conclusions were as follows:(1) SPAD values in the rice canopy changed in an "M" shape:initially increased and then decreased twice (except the blank experiments) during the whole growth period. The higher N application level is, the greater the fluctuation range is. By examining the correlation of SPAD values with N concentrations per unit area (Na) and per unit weight (Nw) as well as that of SPAD/SLW (SLW, Specific Leaf Weigh) with Nw in four canopy leaves, it was found that the relevant degree decreased in following order:SPAD vs Na> SPAD/SLW vs Nw> SPAD vs Nw and they were little effected by years of planting, varieties, growth stages and leaf positions. In addition, the optimal determination position is3/10of the distance from from the blade tip. The relationship between the average SPAD values and rice yield showed quadratic regression curve in the rice canopy in the whole growth period.(2) Through the establishment of rice critical nitrogen concentration dilution curve and the regression function between leaf SPAD values and NNI, the results showed that critical N concentration dilution curve (Xiushui63:Nc=5.31W-0.5, Hang43:Nc=5.38W-0.49) was similar to sheehy’s (1998) Nc=5.20W-0.52reported in the literature. Where Nc is critical N concentration, W is the total shoot biomass. The regression relationship between four leaves (L1, L2, L3, L4) SPAD values in the rice canopy and NNI was greatly influenced by development stages and leaf positions. The regression relationship between SPAD values of L1and L2in the canopy leaf and NNI was relatively closer at tillering and the L1and L2were ideal indicator leaves of plant nitrogen nutrition diagnosis at tillering stage. At booting stage and heading stage, the L4and L3in the plant canopy were respectively ideal indicator leaves for diagnosis of plant nitrogen nutrition. The regression relationship of grain yield with SPAD velues of L4was significant at booting stage (RL42=0.82**in2011; RL42=0.72**in2012). Relative SPAD values of L4(RL42=0.92**in2011; RL42=0.77**in2012) and NNI (R2=0.96**in2011, R2=0.86**in2012) demonstrated an even closer relationship with grain yield at booting stage.(3) The experiment with5N levels and three varieties (Hang43, Xiushui09, Zhongzheyoulhao) was carried out in the net room. Through the analysis of physiological indicators (leaves SPAD values, N concentration, chlorophyll a/b, chlorophyll fluorescence parameters) at tillering, booting and heading stage, the results indicated that with the increasing of N rates, SPAD values and N contration increased, but the chlorophyll a/b decreased. The chlorophyll fluorescence parameters (Fv/Fm, qP, PSII) reached an plateau after an initial increase, while non-photochemical quenching (NPQ) first decreased and then became stable. Chlorophyll a/b showed a negative correlation with N concentration, which was little affected by varieties and development stages (p>0.05). In contrary, the correlation between chlorophyll a/b and SPAD values was remarkedly affected by varieties and development stages. SPAD values presented a linear relationship with Fv/Fm with the coefficient of determination (R) of0.8～0.98among varieties and growth periods.