Relationship Between Plant Height And Canopy Spectra Of Winter Wheat Under Frost Stress

Winter wheat late frost damage occurs from the cold season to the warm season,where a large drop in temperature brings the body temperature below the freezing point,causing damage to the winter wheat protoplasm,resulting in plant damage or death.Late frost damage occurs mainly from the jointing stage of wheat to the heading stage(from late March to mid-April).In this period,freezing damage to wheat may cause reduction of yield and even loss of production.Compared with the complexity of the effects of frost damage on yield traits,the response of plant height changes to freezing damage is more consistent and obvious,so this study will take plant height as a breakthrough point.In this paper,we will research the relationship between spectral changes of wheat canopy and changes in plant height through the cryogenic frost experiments in 2013,2014 and 2016.In the experiment,we constructed plant height changes model based on specific location spectral parameters,combination of wavelength narrow band spectral index and Sensitive spectral bands,respectively.We chose the optimal model to reflect changes in plant height of winter wheat late frost damage by comparing the Adj.R~2 and RMSE of different models.Through research,this paper draws the following conclusions:(1)Low-temperature sensitive period of winter wheat development in young panicles is the stamen period and the connective period.During this period,the plant height gradually decreased with the decrease of frost temperature,and the decrease in plant height has a mutation.In the stamen period,the mutation temperature of the plant height reduction is around-11°C,while in the connective period rose to-7°C.(2)Changes of original spectra of frost wheat canopy is that,in the visible light band of 400-750nm,the reflectivity values decrease with the decrease of the temperature.A small reflection peak appears in the yellow edge of 540-550 nm and in in the short-wave infrared wavelength range of1500-1769 nm.While there were three peaks in the near infrared wavelength band of 750-1300 nm continuously.(3)Changes of first derive reflectance spectra of frost wheat canopy is that,as the temperature decreases,the reflectance value is lower.Red light is strongly absorbed at about 680 nm,and red valley phenomenon occurs.In the wavelength range of 710-760nm,the red edge effect begins to appear.As the temperature decreases,the red edge moves to the short-wave direction and the red edge“blue shifts”, and the lower the temperature,the smaller the reflectivity value.(4)The correlation analysis results showed that in the mixed samples of experiment 1 and experiment`6 2,the correlation between the plant height change rate and?r,SDr,Dr,Drmin,Dr/Drmin,and Dr/SDr reached a significant level((P<0.01).In experiment 3,the 2-stage test-sensitive narrow-band spectral indices that are significantly associated with plant height are:SR555,PSSRa,TVI,SR735,RMCARI/ROSAVI,WI,SRWI,SR1096,NWI-1,NWI-3,AI,HI,a total of 12.In the spectral correlation analysis of plant height and whole-band,430~485nm,523~564nm,732~904nm,1123~1334nm reached extremely significant correlation with the plant height(P<0.01),among which the extremely significant maximum correlation was reached at 762nm and the correlation coefficient is0.423.(5)In this paper,multivariate stepwise regression analysis was used to construct the plant height model of winter wheat late frost damage.Among all the models,the best fitting model was a regression model constructed with a narrow band spectral index,the model Adj.R2=0.581,RMSE=5.393,and the narrow band spectral index involved in the modeling is PSSRa.