Calibration Of Non-Destructive Monitoring Instrument For Crop Growth Information

Information agriculture is the advanced development stage of agriculture information industrialization, which is the production management system for modern agriculture based on information collection technology, decision support technology and intelligent equipment for carrying out quantitative decision, variable input, site-specific implementation on production practices. Among them, technology and relevant equipment for farmland information collection are the foundation and support for precision agriculture, and the important guarantee for achieving high efficiency, high yield and high quality production. The intelligent, precise and digital features are the future trend of modern agricultural development.Non-destructive monitoring technique of crop growth based on spectral information is an urgent need for accurate diagnosis and dynamic regulation on crop growth status. Moreover, the calibration on the existing monitoring instrument for improving performance is the key step for realizing intelligent, precise, and digital functions of the instrument. The present instrument under study has the characters of simple structure, low cost, low power and portability, and can detect canopy reflectance of crop plants and display readings on its LCD after converting by single-chip microcomputer, which adopt initiative light source (sun-light), set8specially designed interference filters based on four characteristic bands at546nm,660nm,710nm,810nm by detecting incident and canopy reflectance.By measuring the spectral-responsiveness of the silicon photocell with the spectral-responsiveness detecting system, then adjusting the position and photosensitive face toward silicon photocell according to the measured results, the spectral-responsiveness of the silicon photocell could be maintained at the same level. The calibration scenario of optical system parameters was provided, including calibration of single photocell, multi-component combination, and the whole photoelectric detection system. The calibration of optical system was carried out based on the laboratory experiment. By comparing the integrated response of optical system with different wavelengths, the correction factor was calculated and stored in the single-chip microcomputer, and then used for correcting output data according to the actual test, which would improve the accuracy of the instrument.By testing and monitoring environment temperature and relative humidity which were considered as the impact factors of the monitoring accuracy, the experimental results showed that the environmental relative humidity had little effect on the output voltage of photoelectric treatment system in the instrument, which can be ignored at practical measurement. There is a negative correlation relationship between environment temperature and instrument voltage output. Establishing a linear table according to the output error and storing it in the single-chip microcomputer would help to correct the output data based on the actual testing temperature, which would improve the accuracy of the instrument.On the basis of calibrating the monitoring instrument, field testing was undertaken in wheat using fore-and-aft monitoring instrument. The correlation and quantitative relationship of leaf nitrogen content to canopy spectral reflectance and derived spectrum index were investigated, and then the practical performance of the calibrated monitoring instrument was evaluated for field application in wheat. The results indicated that the correlation between canopy spectral reflectance and leaf N content at each growth stage of wheat was obviously stronger with the calibrated instrument than with the non-calibrated instrument. The spectral reflectance at four bands tested by the calibrated instrument showed highly significant correlation with leaf N content at stages of filling, flowering and filling, and the whole growth period, with the average correlation coefficients from0.20to0.77. Thus, the calibrated instrument can be expected to give a good performance for practical application in the field crop.