Abstract: Taking the air-dried samples of five soil types from middle and easte
rn China as test materials, the correlations of their organic matter content wit
h the spectral reflectance of near-infrared (1000〖KG-*2〗-〖KG-*7〗2500 nm), a
nd with the ratio index (RI), difference index (DI), and normalized diff
erence index (ND) of the first derivative values of the reflectance between
two bands were studied. Based on this, the key spectral indices and the quantita
tive models for estimating soil organic matter (SOM) content were developed. Aft
er corrected with Multiplicative Scatter Correction (MSC) and Savitzky-Golay (S
G) smoothing methods, the spectral reflectance of near-infrared had an obviousl
y high correlation with SOM, compared with the original spectral reflectance, wh
ile the corrected spectral indices of the first derivative values of the reflect
ance between two bands took the intermediate position. The correlation of the sp
ectral indices with SOM was in the order of was DI＞RI＞ND, regardless the c
omposition of the original spectral reflectance or the first derivative spectra.
 The DI of the reflectance of near-infrared between 1883 and 2065 nm correc
ted with MSC and SG smoothing methods ［DI(CR1883, CR2065)］
 had the best linear correlations with SOM. The test of the moni
toring model based on DI(CR1883, CR2065) with the independen
t datasets of SOM showed that the R2 and RMSE validation values were 083
7 and 406, respectively. Comparing with the results from the Partial Least Squ
are (PLS) method, the monitoring model based on DI (CR1883, CR
2065) was somewhat inferior. However, the DI (CR1883, CR2065
) only needed two reflectance bands, and the monitoring model was
 simpler, being able to provide more available information for developing portab
le instruments, and a good spectral index for estimating SOM content.

Key words: soil organic matter, near-infrared spectrum, multiplicative scatter correction, difference spectral index DI (CR₁₈₈₃, CR₂₀₆₅), wild barley, phosphorus use efficiency, rhizosphere soil, inorganic phosphorus fraction.