Analysis Of Rice Growth Characteristics And Yield Estimation Under Different Conditions Of Rice Leaf Roller Damage

Rice is the main grain product in China.Cnaphalocrocis medinalis Guenee(C.medinalis),as one of the main pests in the main rice-growing areas of China,has been threatening the safety of rice production in China.In this paper,C.medinalis and its infesting process was observed in the controlled field experiments and the natural field experiments respectively.The canopy hyperspectral parameters,physiological and ecological parameters and the pest characteristic parameters of healthy rice and damaged rice were measured.The SPAD values and canopy spectral reflectance of rice in the controlled field experiment and the natural field experiment under different damage degrees were analyzed and compared.Consequently,the correlation between the SPAD values and canopy reflectivity of rice was analyzed,the five key vegetation indexes were selected and the estimation models of pest characteristic parameters were established.Combined with the measured meteorological data in the experimental areas and the experimental period,the influence of meteorological factors on the growth parameters of healthy rice and the correlation between the meteorological factors and the growth parameters of healthy rice were analyzed.The rice yield loss under each pest damage degree of controlled field experiments and natural field experiments was evaluated.The correlation between the pest characteristic parameters and the rice yield was investigated and the yield estimation models based on pest characteristic parameters were established.At the same time,the principal component analysis of meteorological factors and pest characteristic parameters were carried out,and the rice yield estimation models based on the meteorological factors and pest characteristic parameters were established according to the extracted principal components.The main findings were as follows:(1)The relationship curves of SPAD value and near-infrared reflectance with the effective accumulated temperature,cumulative sunshine hours and cumulative precipitation of the healthy rice during the three-year experiments were parabolic.Among them,the SPAD value and near-infrared reflectance had the good correlations with the effective accumulated temperature and cumulative sunshine hours,but a poor correlation with the cumulative precipitation,SPAD value and near-infrared reflectance.(2)The SPAD values of rice in the controlled field experiments and the natural field experiments decreased with the increase of the pest damage degree on the whole,and the canopy reflectivity of the near-infrared light band also decreased with the increase of the pest damage degrees,while the canopy reflectivity of the visible light band increased with the increase of the pest damage degrees on the whole.During the whole growth period,the SPAD values at each degree of pest damage in the controlled field experiments and the natural field experiments were generally increased first and then decreased,and the reflectance of the rice canopy at each degree of pest damage also increased first and then decreased.At the same degree of pest damage,the SPAD value in the natural field experiment was significantly lower than that in the controlled field experiments in the early stage of rice growth,and the SPAD value in the natural field experiment was gradually higher than that in the controlled field experiments after the filling stage.The reflectivity of the near-infrared band of the rice canopy in the jointing stage in the natural field experiment was significantly lower than that in the twoyear control field experiments,while the reflectivity of the near-infrared band in the natural field experiments was higher than that of the control field experiments during the period from booting stage to maturing stage.(3)The pest number and leaf-rolled rate of control field experiments and natural field experiments had a very significant negative correlation with the SPAD value of rice(P < 0.01),a significant negative correlation with the red edge position of rice canopy and the reflectance of near-infrared band(P < 0.05),but a weak positive correlation with the canopy reflectance of some red-light bands of visible light.Five vegetation indexes and SPAD were selected to establish the estimation model on rice yield with the pest number and leaf-rolled rate of the three-year experiments respectively.The best effects of predicting pest number and leaf-rolled rate were the univariate quadratic function models of OSAVI and SPAD,respectively,while the multiple linear regression model predicted pest number and leaf-rolled rate better than the onefactor estimation model.Most influencing indicators estimate the effectiveness of leaf-rolled rate more accurately than pest number.(4)When the degree of pest damage increased,the number of effective panicles,weight per1000 grain,seed setting rate and theoretical yield of rice in controlled field experiment and natural field experiment decreased in the varying degrees.The number of effective panicles and weight per 1000 grain increased slightly when the degree of pest damage was light but the seed setting rate of rice decreased significantly when the degree of pest damage was medium or above.The number of effective panicles and weight per 1000 grain of natural field experiment were higher than those of control field experiment.When the degree of pest damage was light,the yield of natural field experiment was lower than that of control field experiment but when the degree of pest damage reaches medium or above,the yield of the former was higher than that of the latter.(5)Based on the data of the pest number and the percentage of C.medinalis,the linear regression models of rice yield estimation in each experimental year was constructed.The simulation effect of on the yield estimation models based on the pest number was the best which the decision coefficients of the estimation model and the verification model were 0.640 and0.862,respectively,while the fitting effect of the yield estimation models based on the leafrolled rate was not satisfactory.The meteorological factors and insect pest characteristic parameters were selected to analyze the principal component effect analysis on the rice yield,two principal components were selected to establish the optimal yield estimation models,and the decision coefficients of the estimation model and the verification model were 0.730 and0.902,respectively,which shows the estimation effect of the models on the rice yield was relativelygood.