Modeling for Soil Organic Matter Content Based on Hyperspectral Feature Indices

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National Natural Science Foundation of China(No.41501226), the Foundation of State Key Laboratory of Soil and Sustainable Agriculture (No.Y412201431) and Natural Science Foundation of the Higher Education Institutions of Anhui Province (No.KJ2015A034)

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    [Objective] The analysis of soil properties using routine chemical analysis method is rather costly and time-consuming, and so hard to meet the requirement for handling large volumes of soil samples fast and efficiently to monitor soil properties. Continuous soil spectral curves obtained with the aid of the hyperspectral technology encompass abundant spectral information, and reflect comprehensively various soil attribute information. Therefore, modeling can be done to predict some soil properties efficiently and accurately based on the hyperspectral technology. This paper was oriented to build a model for predicting soil organic matter (SOM) content based on hyperspectral feature indices with an expectation to provide a new method for rapid and effective determination of SOM content. [Method] In this study, a total of 178 soil samples were collected from the surface soil layers (0~20 cm) of farmlands of paddy soil and fluvo-aquic soil in the central plain of Jiangsu province for analysis of SOM content. Hyperspectral curves of the soil samples were obtained with the aid of the ASD FieldSpec 3 spectrometer. Firstly, the original spectra were processed with the algorithms of reciprocal log transformation (Log(1/R)) and continuum-remova l (CR) for analysis of hyperspectral characteristics of the soil samples different in SOM content and in soil type. Secondly, based on the data of the original, Log (1/R) and CR spectra, spectral feature indices, including deviation of arch (DOA), difference index (DI), ratio index (RI), and normalized difference index (NDI), were calculated, and relationships of SOM content with the four indices were analyzed. Finally, linear regression models for SOM content were established based on the selected spectral feature indices. Accuracies of the models were evaluated and compared. [Result] Results show:(1) SOM content was significantly and negatively related to original spectra, but significantly and positively to reciprocal log spectra. The relationship was the most significant at the waveband of 400~900 nm, with the absolute correlation coefficient value reached above 0.6. After the spectral curves being CR transformed, their differences in characteristic became extraordinarily significant different, and significant absorption valleys appeared near 420 nm, 480 nm, 660 nm, and 900 nm; (2) The DOAs of the original, Log (1/R) and CR spectra showed extra-significant relationships with SOM content (P<0.01) at wavelength of 600 nm, with correlation coefficient being -0.66, 0.61 and-0.33, respectively; and (3) Based on the combinations of DOA with DI, RI, and NDI of the three different spectra, the model established for predicting SOM content performed quite effectively, with relative percent deviation ranging from 1.78 to 1.94, R2 from 0.56 to 0.64, and RMSE from 4.98 g·kg-1to 5.50 g·kg-1. And the validation sets had R2 ranging from 0.67 and 0.73, and RMSE from 3.21 g·kg-1 to 3.51 g·kg-1.[Conclusion] The spectral feature indices, including DOA, DI, RI, and NDI, can be used effectively for modeling for SOM content, and the model may explain about 67%~73% of the SOM variability. The model established with RI and DOA of the Log (1/R) spectrum is an optimal one.

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ZHAO Mingsong, XIE Yi, LU Longmei, LI Decheng, WANG Shihang. Modeling for Soil Organic Matter Content Based on Hyperspectral Feature Indices[J]. Acta Pedologica Sinica,2021,58(1):42-54.

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  • Received:April 20,2020
  • Revised:September 01,2020
  • Adopted:September 03,2020
  • Online: October 30,2020
  • Published: January 11,2021