Abstract
Portable spectrometers can extract crop growth information in a non-destructive, rapid, and efficient way. However, most existing instruments can only be used to collect spectral reflectance and calculate vegetation indices. They are costly and lack crop spectral monitoring models and diagnosis models; therefore, crop growth information cannot be directly output from these instruments. In this paper, an active light source apparatus for crop growth monitoring and diagnosis (CGMD) was developed based on the canopy shape characteristics and spectral monitoring mechanisms of row-cultivated crops. A modulated light source was used in this apparatus to effectively eliminate the interference of ambient light. At the same time, a high-pass filter was used in the apparatus to extract the canopy reflectance spectral information, which improves the signa-noise ratio. Crop canopy vegetation indexes-the normalized difference vegetation index (NDVI) and the ratio vegetation index (RVI)-and crop growth parameters-leaf area index (LAI), leaf dry weight (LDW), leaf nitrogen accumulation (LNA), and leaf nitrogen content (LNC)-were obtained in real time. The ambient light influence test and the comparison test of different test heights of the CGMD apparatus show that it has high test stability and can effectively overcome ambient light interference within the standard test height range. The rice and wheat experimental results demonstrated that the test results of the CGMD apparatus and the commercial Analytical Spectral Devices field spectrometer (Malvern Panalytical, Malvern, Worcs, UK) were consistent. Comparing the vegetation indexes and agronomic parameters obtained from the chemical analysis, the CGMD apparatus has a good predictive ability for LAI, LDW, LNC, and LNA.
Highlights
Implementing accurate crop production management is comprised of the acquisition of crop growth information, analysis and processing of this information, and the generation of fertilization prescriptions
1) TEST RESULTS OF THE INFLUENCE OF AMBIENT LIGHT ON INSTRUMENT PERFORMANCE The normalized difference vegetation index (NDVI) and ratio vegetation index (RVI) results of crop canopy measured by crop growth monitoring and diagnosis (CGMD) apparatus at different measuring times during different growth periods of wheat are shown in Fig. 23; as shown, CGMD apparatus had consistent test results at different test times on the same test day
3) TEST RESULTS OF THE CONSISTENCY BETWEEN DIFFERENT INSTRUMENTS To verify the measurement accuracy of CGMD apparatus, the commercial Analytical Spectral Devices (ASD) Fieldspec HandHeld2 spectrometer was used for synchronous testing
Summary
Implementing accurate crop production management is comprised of the acquisition of crop growth information, analysis and processing of this information, and the generation of fertilization prescriptions. The accuracy of a crop management system relies on the access to crop growth information. The acquisition of traditional crop growth information mainly depended on visual observation and destructive. Field sampling followed by indoor chemical test analysis, which is complex and time consuming [1]–[3]. The development of spectral monitoring techniques has provided new approaches for obtaining crop growth information. There are sensitive bands in the crop canopy reflectance spectra that are closely related to crop growth information; scientists can use the spectral characteristics of these sensitive bands to dynamically monitoring the crop growth indices and plant nutrient status [4]–[6]. In 1986, Shibayama et al found that the vegetation index constructed based on the sensitive bands at 620 nm and 760 nm of rice reflectance spectrum had a strong correlation
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