Distribution characteristics of SPAD value in rice leaf and its relationship with nitrogen application rate

ObjectiveThe present study explored distribution characteristics of SPAD value in rice leaves and its relationship with nitrogen application rate,in order to provide reference for establishing linear model of rice nitrogen application rate management based on SPAD value.MethodSplit plot design was adopted in this experiment,having two rice varieties (Qyou 6 and Zhunliangyou 527) in main plot and six different nitrogen application rates (0,75,150,225,300 and 375 kg/ha,calculated based on pure nitrogen) in subplot.Leaf SPAD values in different nitrogen treatments at important growth stages and relationship between distribution characteristics of SPAD value and nitrogen application rate were studied.ResultResults showed that the order of Qyou 6 rice yield in different nitrogen applications was as follows:300 kg/ha>225 kg/ha>150 kg/ha>375 kg/ha>75 kg/ha>0 kg/ha,and rice yield of Zhunliangyou 527 increased with the increase of nitrogen application rate.Effective panicle number and 1000-grain weight of Zhunliangyou 527 were significantly higher than those of Qyou 6.The dynamic changes of SPAD value of Qyou 6 and Zhunliangyou 527 at different nitrogen levels were similar,but the time of peak SPAD value and change amplitude of SPAD value had slight difference.SPAD value and nitrogen application rate showed significant positive correlation at jointing stage,heading stage and maturity stage in Qyou 6 and Zhunliangyou 527 (P<0.01),but the slope of fitted equation was low.SPAD values of different determination time varied between different varieties and leaves at different positions.The results of one variable quadratic polynomial fitting between secondary indexes of SPAD value and nitrogen application rate showed that cure fitting degree between SPAD value of lower leaf(L3 and L4) and nitrogen application rate was higher than the degree between upper leaf(L1 and L2) and nitrogen application rate.The SPADL4×L4xL3/mean value at two fertilizing stages could be used as an ideal indicator for nitrogen nutrition diagnosis.ConclusionThe fitting relationship between SPADL4×L4xL3/mean value of rice leaf and nitrogen application rate was obvious,which is not affected by time and variety.So SPADL4~ value can be an ideal parameter for SPAD-value-based nitrogen application rate model with rice as variable.