Spectroscopy-Based Soil Organic Matter Estimation in Brown Forest Soil Areas of the Shandong Peninsula, China

Prediction of the Soil Organic Matter (SOM) Content from Moist Soil Using Synchronous Two-Dimensional Correlation Spectroscopy (2D-COS) Analysis

“…Conventional spectroscopic analysis for SOM assessments routinely employs 1-D spectral data for building regression models [ 52 , 54 , 56 , 59 ] and they are often in conjunction with various pre-processing methods for performance enhancements [ 55 , 56 , 58 ]. To highlight the limitation of the 1-D spectroscopic analysis, Figure 4 presents the 1-D spectra of six soil samples with different SOM contents of (a) 0.40%, (b) 1.12%, (c) 2.12%, (d) 3.35%, (e) 4.51% and (f) 7.92% as function of various moisture contents (from oven-dry to 17% w / w moisture).…”

“…Note that the four experimental configurations (A–D) are designed to illustrate the effect of the SOM prediction accuracies when different combinations of spectral bands have been used for the analysis. Specifically in experiment (D), where only the SOM featured bands have been selected like that of the traditional method commonly adopted by workers in the field [ 52 , 53 , 54 , 55 , 56 , 57 , 58 , 59 , 60 , 61 , 62 ], the experiment is designed to compare the impacts when SOM only bands are utilised with respect to the proposed band selection method as set out in Experiment (C).…”

“…Apart from the correction approach as outlined in the previous paragraph, alternative methodology has been the discovery of the SOM related spectral bands [ 52 , 53 , 54 , 55 , 56 , 57 , 58 , 59 ] particularly those which are not greatly affected by the absorption feature of moisture in the soil [ 60 , 61 , 62 ]. There are numerous reports about the SOM-related absorption features in the vis-NIR spectral range and studies have revealed that spectral bands in the 800–1400 nm, 1600–1700 nm, 2100–2200 nm and 2300–2500 nm region [ 61 ] are relatively free of interference because of the presence of moisture content in the soil.…”

“…There are numerous reports about the SOM-related absorption features in the vis-NIR spectral range and studies have revealed that spectral bands in the 800–1400 nm, 1600–1700 nm, 2100–2200 nm and 2300–2500 nm region [ 61 ] are relatively free of interference because of the presence of moisture content in the soil. However, a number of different sets of narrow wavebands, such as that centred at 1130 nm, 1350 nm, 1398 nm, 2210 nm [ 60 ], and more recent work reported that the set of 849 nm, 1681 nm, 2187 nm [ 58 ] and also another set at 917 nm, 991 nm, 1007 nm, 1996 nm, 2267 nm [ 59 ] gave good prediction of the SOM with R 2 ~ 0.90. Recent study also expressed that new wavebands between 550–700 nm and 800–850 nm, 1700–1800 nm [ 62 ], narrow bands at 434 nm, 2368 nm and 2490 nm [ 55 ], and also those at 520 nm, 550 nm, 588 nm, 610 nm and 654 nm [ 54 , 56 ] were important for the estimation of SOM contents from the soil.…”

“…Recent study also expressed that new wavebands between 550–700 nm and 800–850 nm, 1700–1800 nm [ 62 ], narrow bands at 434 nm, 2368 nm and 2490 nm [ 55 ], and also those at 520 nm, 550 nm, 588 nm, 610 nm and 654 nm [ 54 , 56 ] were important for the estimation of SOM contents from the soil. The optimum SOM related bands were mostly obtained based on the one-dimensional (1-D) spectral correlation technique [ 52 , 54 , 56 , 59 ] and also through the optimisation methods using stepwise regression analysis in combination with various pre-processing- methods [ 55 , 56 , 58 ].…”