Hyperspectral Remote Sensing Estimation Models For Nitrogen Nutrition Monitoring Of Maize

In this study, maize was acted as research object, obtaining maize canopy hyperspectral reflectance under different nitrogen levels with the Field Hyperspectral Remote Sening after 2 years field experiments. The correlation analysis between spectral parameters and nitrogen content of maize vegetative organs aboveground were studied at different stages or the whole growth period, by which several spectral parmeters were screened and the estimation models of maize nitrogen contents were constructed. At last, the precision of those models were tested. The results were as follows:(1) Maize canopy reflectance spectrum has the typical "peak-valley" of green plants at 400-680nm. The green summit reflectance declined and the green summit position appeared red-shift with growth period. In the near-infrared region (760～1000nm) as the growth stage went on, the reflectance has the trend of descending. The maize canopy reflectance at near infrared bands and N-fertilizer amount showed a positive correlation at booting stage.(2) These estimation models of maize nitrogen content were established based on high-spectral data was built by using maize canopy spectral reflectance and its logarithm, reciprocal or derivative transformation and spectral position and area and vegetation index.Estimation model of nitrogen content in leaf at jointing stage can be estimated with the date of RDVI (943,749). The estimation equation is y=204.05x2+7.5201x+2.4484 (RMSE=0.2531, R2=0.8329), the correlation coefficient of measured value and Predicted value is 0.9126**.Estimation model of nitrogen content in leaf at anthesis-silking stage can be estimated with the date of p’(598nm). The estimation equation is y=376236x2+1871.1x+3.3134 (RMSE=0.2235, R2=0.7514), the correlation coefficient of measured value and Predicted value is 0.8668**.Estimation model of nitrogen content in leaf at ripening stage can be estimated with the date of p’(598nm). The estimation equation is y=1.9852e-308.3x (RMSE=0.2328, R2=0.7086). the correlation coefficient of measured value and Predicted value is 0.8418**.(3) Estimation models of nitrogen content in leaf shavesThere was not the estimatin of nitrogen content of leaf shaves at filling stage because of the high REMSE. Estimation models of leaf shaves nitrogen content were construced at at joining stage, booting stage, tasseling stage, anthesis-silking stage, ripening stage and the whole growth period. Compared with maize leaf, the leaf shaves nitrogen content was more easily estimated.The estimation equation at jointing stage is y=376236x2+1871.1x+3.3134 (RMSE=0.2694, R2=0.7023) with the date of p’(597nm), r=0.838** (the correlation coefficient of measured value and Predicted value)The estimation equation at booting stage is y=181925x2-638.11x+1.3104 (RMSE=0.2149, R2=0.7726) with the date of (1/p)″(842nm), r=0.879**.The estimation equation at tasseling stage is y=109.73x2-213.84x+104.89 (RMSE=0.1551, R2=0.7735) with the date of RVI(760,755), r=0.8795**.The estimation equation at anthesis-silking stage is y=4.0567x2-187.39x+1.0843 (RMSE=0.2388, R2=0.8082) with the date of p’(340nm), r=0.8989**.The estimation equation at ripening stage is y=0.9343e-0944* (RMSE=0.1621, R2=0.7684) with the date of p″(959nm), r=0.8766**.The estimation equation in the whole growth periof is y=-0.0025x2+0.1111x+0.3127 (RMSE=0.2491, R2=0.7484) with the date of RVI(774,697), r=0.8651**.(4) Estimation models of nitrogen content in stem.There was not the estimatin of nitrogen content of stem at jointing stage and anthesis-silking because of the high REMSE. Estimation models of stem nitrogen content were construced at at booting stage, tasseling stage, filling stage, ripening stage.The estimation equation at booting stage is y=1.1097e-0.053x(RMSE=0.2475, R2=0.7762) with the date of (1/p)’(381nm), r=0.881**.The estimation equation at tasseling stage is y=1089.6x2-2236.8x+1148.5 (RMSE=0.2401, R2=0.8026) with the date of RVI(760,755),r=0.8959**.The estimation equation at filling stage is y=-63.851x2-11.133x+0.6153 (RMSE=0.1923, R2=0.7768) with the date of (1/p)″(550nm), r=0.8814**.The estimation equation at ripening stage is y=-2E+06x2-845.2x=0.61 (RMSE=0.1738, R2=0.7409) with the date of p″(880nm), r=0.8608**.