水稻土可见-近红外-中红外光谱特性与有机质预测研究

Study on the Characterization of VNIR-MIR Spectra and Prediction of Soil Organic Matter in Paddy Soil

土壤有机质是农田肥力评估的重要指标,要实现快速获取大面积土壤有机质的含量需要建立高效、稳健的预测模型。光谱技术能够快速诊断土壤有机质,以水稻土为例,从校正样本选择方法的对比,研究了可见-近红外、中红外和可见-近红外-中红外三种不同波段光谱对土壤有机质的预测能力。可见-近红外和中红外区域的光谱反射率转换成吸收率后通过Savitzky-Golay平滑法去噪,通过三种校正样本选择方法建立相应的偏最小二乘回归预测模型。通过Rank-KS法建立的三种波段的有机质预测模型均优于Rank法和KS法,中红外波段光谱的模型预测能力强于可见-近红外和可见-近红外-中红外波段的预测模型,基于RankKS法建立的中红外波段有机质预测模型取得了最好的预测效果,RMSEP仅为3.25g·kg^(-1),RPD达到4.24,依据VIP得分筛选出可见-近红外和中红外波段的水稻土有机质重要建模波段。因此,中红外光谱建模技术能够对水稻土有机质进行快速定量分析,Rank-KS法可提高模型的预测能力,为今后农田肥力评价和科学施肥提供技术支持。

Soil organic matter （SOM） is an essential indicator for the fertility assessment of farmland, and An efficient and stable prediction model is in need to rapidly estimate SOM in larger scale. Spectroscopic technology has been proved as a powerful tool to access SOM in the last decade. The aims of this paper were： to compare different selection method of calibration set for mod- eling SOM in paddy soil by using visible-near infrared （VNIR）, mid-infrared （MIR） and VNIR-MIR spectra and to assess the prediction ability of the results. All spectra were transformed from reflectance to absorbance, and preprocessed by Savitzky-Golay smoothing algorithm. The prediction models of SOM were built by using partial least squares regression （PLSR） coupled with three selection methods of calibration set in VNIR, MIR and VNIR-MIR regions. The selection method of calibration Rank- KS performed better than Rank method and KS method, meanwhile the models in MIR region showed stronger prediction ability than VNIR and VNIR-MIR regions. The best prediction model was obtained with the MIR model combined with Rank-KS, and the root mean square error of prediction （RMSEP） and ratio of performance to deviation （RPD） were 3.25 g · kg^-1 and 4. 24. According to variable in the projection （VIP） score, important bands for SOM prediction in paddy soil were identified in VNIR and MIR region. Our results show that MIR spectroscopy could make quantitative prediction of SOM in paddy soil and Rank-KS is an effective method for selection of calibration sets, so as to provide some scientific basis for fertility assessment of farmland and rational fertilization.