Research On Spectroscopy Based Rapid Measurement Method For Nitrogen Content In Soil And Plants And Sensor Development

The abundance or deficiency of nitrogen in soil is an important basis for guiding scientific fertilization,achieving high crop yield,ensuring safe and effective production.The content of nitrogen is also one of the indicators in the process of mastering farmland information and precise fertilization.The traditional chemical analysis method is complicated,costs more time and money but gains poorer real-time performance,so it is difficult to be applied on a large scale.Spectroscopy is a rapid and nondestructive detection means.Due to the fingerprint characteristic of various forms of nitrogen molecules in near infrared and infrared region,absorption,scattering and other spectroscopic phenomenon can be used to measure the content of nitrogen in soil quickly.In this paper,total nitrogen and available nitrogen in soil were taken as the object of study,and a variety of measuring methods of molecular spectrum were carried out on them.At last a small instrument for rapid detection of soil nutrients was designed and developed.At the same time,micro imaging spectroscopy was applied to nitrogen imaging analysis of micro scale in soil and crop,which provided a new way and experimental foundation for the study of nitrogen transport in crops and soil.The main contents of this research included:(1)Total nitrogen and available nitrogen in soil were measured by mid infrared spectroscopy.We used attenuated total reflectance(ATR)and diffuse reflectance(DRIFT)to obtain spectra,compared the advantages and differences between attenuated total reflectance and diffuse reflectance spectroscopy on soil nitrogen measurement,chose several pre-treatment methods to reduce the noise,and established the corresponding quantitative models.It showed that multiplicative scatter correction(MSC)and standard normal variate transformation(SNV)had better results both in ATR and DRFIT models of nitrate among the several pre-treatment methods.For a further study,we put forward a new method of spectral fusion about attenuated total reflection and diffuse reflection mode,and collected two kinds of spectral data of one same sample,took the advantage of MSC and SNV to cut down the noise,made their advantages complementary and improved the accuracy and precision of measurement.In the PLS model of fusion spectra,the RC2 improved to 0.914、0.891 of total nitrogen and available nitrogen respectively,and improved to 0.951、0.919 for a further step after SNV-pretreatment.Besides,we used the IPLS method to optimize the spectral band in order to achieve the desired prediction results while reducing the computational complexity as possible,which reduced the number of independent variables from 15677 to 2922.(2)Nitrogen in soil was studied by using infrared micro imaging spectroscopy.By using infrared micro imaging spectroscopy,we detected the nutrients in soil,captured the spectral information of functional groups and the image information about nutrient content.We focused on the spectral characteristics of nitrate nitrogen in soil under micro scale,and built the quantitative regression model.According to the infrared image,we understood the distribution and variation of nitrate in soil.In that way,people could get better understanding on how the nitrate distribution in soil and how it spread after fertilization.(3)Nitrate nitrogen in crop tissues was studied by molecular spectroscopy.On the basis of microscopic observation of nitrate nitrogen in soil,we explored the distribution and the content of nitrate in oilseed rape leaves by using confocal micro Raman spectrometer,it could effectively avoid the interference of water and carbonate.According to the signal intensity of different concentrations of nitrate nitrogen at the Raman shift of 1050cm’1,we established a quantitative measurement model of nitrate nitrogen in leaves and obtained the image information of nutrients distribution in micro regions at the same time.In the foliar fertilization experiment,we presented a real-time way of nitrate detection and could know how it spread in leaves for the further study.(4)The soil nitrogen instrument was developed by multi band measuring technology.We picked the central wavelength at 1260nm,1310nm,1350nm,1410nm,1450nm,1510nm,1550nm,1610nm as the characteristic bands,chose high sensitive detector,optical signal modulation and demodulation circuit of photoelectric system to replace expensive spectrometer,to realize the forecast of nutrient content with characteristic bands.At the same time,the field experiment was carried out with the assembled prototype,and the prediction model of R2 reached 0.902,which met the requirement of the soil total nitrogen field measurement.