The objective of this research is to analyze the influences of light source incidence angle, fiber height, moisture content, and particle size on loamy mixed soil spectra. Nitrogen (N) content calibration and cross-validation models at different moisture contents and particle sizes were obtained using partial least squares (PLS) analysis. Spectral data were collected using a spectrophotometer. Fiber height of 100 mm and light source angle at 45° were chosen to obtain the sharpest spectra without apparent scattering effect. The results show that moisture content and particle size strongly influenced the absorbance of the spectra, and a better N prediction model was obtained when the particle sizes were in the ranges of 0.5-1.0, 1.0-2.0 and 2.0-5.0 mm, with the correlation coefficients (r) of 0.819, 0.815 and 0.818, and standard errors of prediction (SEP) of 2.29, 2.41 and 2.42 mg/kg, respectively. Poor N prediction model was obtained when the soil was kept in its natural moisture content with r of 0.575 and SEP of 3.275 mg/kg, compared to the performance of dried soil samples with r of 0.815 and SEP of 2.425 mg/kg.

Keywords: spectral feature, prediction model, soil moisture, nitrogen content, near infrared reflectance spectroscopy, partial least squares
DOI: 10.3965/j.issn.1934-6344.2008.01.043-050
Citation: He Yong, Shao Yongni, Annia García Pereira, Antihus Alexander Hernández Gómez, Cen Haiyan. Spectral feature characterization and nitrogen content prediction in soils with different particle sizes and moisture contents. Int J Agric & Biol Eng. 2008;1(1): 43－50.