High Spectral Response Characteristics Of Soil And Winter Wheat Under The Long-term Positioning Experiment

As one of the widely grown grain crops in the world, the yields of wheat directly affect world food production. Remote sensing, an important tool in modern agriculture for monitoring soil and vegetation, can get real-time data of crop growth condition rapidly and intactly and guide the fertilizer application and irrigation management in the field, and thus promote high yield and high quality of winter wheat. In this paper, we set up different farming systems such as wheat-pea rotation, wheat continuous cropping, and different application level of nitrogen and phosphorous fertilizer, using the techniques of hyperspectral remote sensing images, physiological and biochemical parameter, and wavelet de-noise to analyze the hyperspectral of canopy and the first derivative spectrophotometry under different rotation cultivation system and fertilizer application. Finally, combined with vegetation index and spectral character parameter, a correlation model relevant to different nitrogen application, chlorophyll and leaf area index(LAI) was established to improve the monitoring technology of winter wheat growth. The main conclusions are as follows:(1) Different rotation cultivation system and different amounts of fertilizer application are not only affect soil fertility but also impact nutrients absorption ability of winter wheat. Compared with wheat-pea rotation, the wheat continuous cropping increase the soil N and soil available P content, but decrease the soil organic matter, total N and total P content, and the soil available N is 97.33mg/kg, increased by 163.05%; while the available N content of wheat-pea rotation is 75.56mg/kg, increased by 104.21%. The wheat continuous cropping and the wheat-pea rotation improved the soil available P content, with the magnitude of 23.05mg/kg and 25.03mg/kg, respectively, and the soil organic matter increased by 40.38% and 52.2%, respectively. Combined application of fertilizer is not only conducive to improve soil fertility equally but also helping nutrients absorption for winter wheat.(2) Soil spectrum curve are similar under different growth stages, which increased with wavelength increase, while the spectral reflectivity is different among the different treatment, especially the NPM and NP treatment on rotation cultivation system had higher spectral reflectivity, with the magnitude of 0.45. Spectral reflectivity increased with the increase of nitrogen fertilizer application under different nitrogen levels, and the reflectivity is up to 0.45 for N180, N135, P180, P135 treatment, while other treatment is about 0.4.(3) There were significant differences in spectral reflectivity among different growing stages for winter wheat. The spectral reflectivity on 500-600 nm is decreased with the winter wheat growth, and the spectral curve became flat gradually, but the spectral curve raised dramatically between 680-760 nm for all treatment, which called red edge wavelengths. According to calculated first derivative, the increase of nitrogen application in wheat-pea rotation system and continuous cropping wheat resulted in red-edge move forward to the longer wavelengths, and this phenomenon called redshift. The spectrum reflectivity increased along with the return green stage, jointing stage, heading stage until grain filling in near-infrared wavelength.(4) The chlorophyll, leaf area index(LAI) and nutrient content are different in different rotation cultivation system, and those index are higher in rotation cultivation system and continuous cultivation system compared with applying nutrient individually. In the continuous nitrogen treatment, wheat leaf area, chlorophyll content and nitrogen content increased with the increase of nitrogen fertilizer application, but it is not significant in applying the phosphorous fertilizer alone. By comparing with those results, we found that there are high correlation between spectral reflectance of different nitrogen treatment and winter wheat nitrogen content, and the high correlation also show up between winter wheat chlorophyll and the spectral reflectance of continuous cropping. Additionally, spectral reflectance of wheat-pea rotation correlated well with leaf area index.(5) Inversion results show that the ratio vegetation index(RVI),difference vegetation index(DVI) and normalized difference vegetation index(NDVI) have high determination coefficient with nitrogen content, chlorophyll and leaf area index in different grown stages of winter wheat, especially the determination coefficient of the NDVI is up to 0.9, which has more advantages in the process of the modeling.